X-rays

X-rays are high-energy particles of electromagnetic radiation used in the medical field for the generation of anatomical images. X-rays are projected through the body of a patient and onto a film, and this technique is called conventional or projectional radiography. As radiation by X-rays can cause adverse effects depending on the absorbed dose, it is necessary to take protective measures to reduce harm. Digital radiography uses the digital data format and allows for the digital manipulation of images. Common uses include evaluation of chest, mediastinal, spinal, and bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones/joint conditions. While radiography is still used to visualize head and abdominal structures, more advanced modalities (CT and MRI) are now preferred. Radiography remains an essential component of initial tests in many diseases, given its wide availability, low cost, and ease of operation.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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Overview

Definition

An X-ray is a discrete, high-energy particle of electromagnetic radiation (photon) that propagates through space at the speed of light.

X-ray production

  • X-rays are produced through different processes:
    • Characteristic X-ray radiation: 
      • Result from the movement or transition of electrons from an outer shell ( orbit Orbit The orbit is the cavity of the skull in which the eye and its appendages are situated. The orbit is composed of 7 bones and has a pyramidal shape, with its apex pointed posteromedially. The orbital contents comprise the eye, extraocular muscles, 5 cranial nerves, blood vessels, fat, the lacrimal apparatus, among others. The Orbit and Extraocular Muscles) to vacancies in the inner shell
      • Emission of X-ray photon is material dependent.
    • Braking radiation (Bremsstrahlung): 
      • Electrons move rapidly toward the anode (positively charged electrode) and decelerate when they collide.
      • During deceleration, 99% of the energy dissipates as heat and 1% is released as X-ray photons.
  • X-ray imaging utilizes an X-ray tube consisting of:
    • A heated filament that emits electrons
    • A tungsten target/anode where electrons strike, producing X-rays
  • X-rays penetrate matter and interact with the atomic electrons of the material. During this process, X-rays can be absorbed or scattered.
  • Not all X-rays can penetrate a patient. Most X-rays are scattered and do not contribute to image creation.
A diagram of an x-ray tube

Diagram of an X-ray tube:
In the tube, electrons are accelerated toward a tungsten target (anode), which then decelerate after hitting the target, releasing heat and X-ray photons.

Image by Lecturio.

Effects of X-ray radiation

  • Biological damage by X-rays is attributed to the ionizing radiation that is produced as X-rays interact with matter.
    • The absorbed dose is the energy (from the interaction) deposited in matter.
    • Absorbed radiation: measured in units known as Gray (Gy) or rad (100 rads are equivalent to 1 Gy) 
  • Types of radiation effects:
    • Deterministic effect: 
      • Damage occurs when a threshold of radiation is crossed, such that the ability of a cell to repair itself is overwhelmed. 
      • Results from very high doses of radiation, causing skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin erythema, cataracts, and sterility
    • Stochastic effect: Damage is additive and the probability Probability Probability is a mathematical tool used to study randomness and provide predictions about the likelihood of something happening. There are several basic rules of probability that can be used to help determine the probability of multiple events happening together, separately, or sequentially. Basics of Probability of the effect increases with increased exposure.
      • Damage occurs at the genetic level during cell division and can lead to carcinogenesis Carcinogenesis Carcinogenesis is the development of cancer by transforming healthy cells into cancer cells. This complex process occurs because of mutations in DNA that prevent the normal process of cell division. Normal cells have programmed cell death, but cancer cells proliferate without regulation. Carcinogenesis.
      • The likelihood of effects increases with radiation dosage.
  • Ultimately, the resulting damage includes:
    • Formation of free radicals
    • Disruption of normal metabolic function and mitosis
  • Cancer induction:
    • Organs with the most rapidly dividing cells are most susceptible, which also explains why children, overall, are most susceptible. 
    • Most susceptible organs:
      • Bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow
      • Colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix
      • Lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs
      • Stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach
    • Moderately susceptible organs:
      • Bladder
      • Breast 
      • Liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver
      • Esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus
      • Thyroid

Fetal risk of radiation

Table: Fetal risk of radiation
Weeks post conception Effects of major exposure
2
  • 10–50 rads: risk of failure to implant
  • > 50 rads: high likelihood of implantation Implantation Endometrial implantation of embryo, mammalian at the blastocyst stage. Fertilization and First Week failure
3–5
  • 10–50 rads: growth restriction possible
  • > 50 rads: congenital abnormalities, growth restriction, risk of miscarriage
6–13
  • 10–50 rads: growth restriction possible
  • > 50 rads: growth restriction, risk of miscarriage
14–23
  • 10–50 rads: noncancer health effects unlikely
  • > 50 rads: growth restriction, risk of miscarriage, possible congenital abnormalities
24 weeks to term
  • 10–50 rads: noncancer health effects unlikely
  • > 50 rads: miscarriage, neonatal death (depending on dose)

Radiation protection

  • Minimize the radiation dosage whenever possible (ALARA: as low as reasonably achievable).
  • Measures:
    • Exposed personnel should be monitored using a film badge.
    • Lead shielding and increasing the distance from the source
    • Shielding within rooms
    • Increasing the kilovoltage of the X-ray beam and, thus, increasing its penetration

Terminology and Technical Aspects

Radiography

  • Radiography: the use of X-rays to generate images
  • Types:
    • Projectional radiography: generation of a radiographic image by projecting a beam of X-ray particles through a subject and onto a film:
      • The X-ray image is a shadow picture obtained using a single “light” source.
      • Fluoroscopy: the use of projectional radiography to observe internal structures in real-time (e.g., GI imaging)
    • CT: generation of a multilayered image by a beam projected by a rotatory X-ray tube onto radiation detectors

Image generation by X-rays

Order of producing an image with X-rays:

  1. X-ray tube: X-rays generated after electrons collide with the anode.
  2. Patient: X-ray beam traverses the patient and is attenuated depending on the tissues in their path.
  3. Antiscatter grid: lead strips that improve image contrast by reducing scattered photons
  4. Image capture is by using an imaging plate in a cassette.

Technologies producing radiographic image:

  • Conventional radiography
    • Screen film is used and the film is developed.
    • High sensitivity, low cost, and easy handling
  • Digital radiography (utilizes digital data format, allowing digital manipulation of images):
    • Computed radiography: Cassette is inserted into a scanner and the image is shown on a monitor.
    • Direct radiography: no cassette used. X-rays are converted into electrical charges by a photoconductor.
Wilhelm röntgen hand

Image of an early X-ray: X-ray of a left hand Hand The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. Hand taken at a public lecture by Wilhelm Röntgen

Image: “An early X-ray” by Wilhelm Röntgen; current version created by Old Moonraker. License: Public Domain

Interpretation

Basic radiological densities

  • Air
  • Fat
  • Fluid
  • Calcium ( bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones)
  • Metal

Terminology according to the density of the object

  • Radiolucent: an object of low density that is permeable to X-rays (looks black)
  • Radiopaque: an object of high density that blocks X-rays (looks white)

Principles of radiography

  • Summation of shadows: Images appear more radiopaque due to overlapping densities.
  • Silhouette sign: 
    • Edges of an object are indistinguishable when densities are adjacent to one another.
    • Think of pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia in the right middle lobe, which obscures the right heart border.
  • Orthogonal imaging: taking 2 projections of the same structure to better document its 3-dimensionality

Elements that reduce the diagnostic yield of an X-ray

  • Excessive or insufficient penetration
  • Rotation of the patient
  • Image magnification
  • Movement of the patient
  • Artifacts, such as dust particles

Chest

Projections

X-ray images of the chest can be produced in the following projections:

  • Posteroanterior (PA):
    • The X-ray beam initially penetrates the posterior aspect of the body while the cassette is placed in direct contact with the anterior aspect.
    • Preferred method for evaluating cardiac silhouette size
  • Anteroposterior (AP):
    • The X-ray beam initially penetrates the anterior aspect of the body while the cassette is placed in direct contact with the posterior aspect.
    • Used in portable radiography (very common in hospitalized patients who are unable to move)
    • Structures further away from the cassette appear magnified, creating false positives for cardiomegaly.
  • Lateral:
    • The X-ray beam is incident on a lateral aspect of the body and the cassette is placed in contact with the other lateral aspect.
  • Lordotic and semi-upright positioning:
    • The X-ray beam penetrates the patient at an angle to display 2 different structures at different levels.
  • Decubitus:
    • The patient lays on their right or left side. 
    • A replacement for lateral projection used for patients who cannot stand up

Technical aspects

To obtain an optimal anatomical image:

  • Inspiration: The patient is asked to take a deep breath while an X-ray is being obtained.
  • 8–9 posterior ribs should be made visible for the inspiration to be optimal.

The following aspects reduce the quality of the anatomical image:

  • Penetration: Excessive or deficient penetration of X-rays through the anatomical structures affects results.
    • Overpenetrated regions can simulate collections of air ( pneumothorax Pneumothorax A pneumothorax is a life-threatening condition in which air collects in the pleural space, causing partial or full collapse of the lung. A pneumothorax can be traumatic or spontaneous. Patients present with a sudden onset of sharp chest pain, dyspnea, and diminished breath sounds on exam. Pneumothorax).
    • Underpenetrated regions can simulate consolidations ( pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia).
  • Rotation: When the patient is not appropriately placed in front of the cassette, the structures are unevenly represented in the anatomical image.
    • The mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels and hilum mimic masses.
    • An image can be rotated to the right or to the left.
    • Inspect by checking the distance between the medial aspects of the clavicle and the spinous processes of the thoracic vertebrae.
Differences between expiratory and inspiratory chest x-ray

Differences between an expiratory and an inspiratory chest X-ray:
Notice that in the inspiratory X-ray, the posterior ribs and the pulmonary parenchyma are more easily seen, whereas in the expiratory X-ray, the parenchyma looks hazy and lacks definition.

Image by Hetal Verma.

Sequence

The quality inspection of the image must be included and should be done preferably before the following reading sequence:

  1. Foreign objects: tubes/lines
  2. Lung parenchyma
  3. Airways
  4. Mediastinal boundaries
  5. Surrounding soft tissue
  6. Bony structures (ribs and clavicles)
  7. Upper abdomen

Tubes and lines

The following elements should be checked for adequate placement:

  • Endotracheal tube
  • Tracheostomy tube
  • Feeding tubes:
    • Nasogastric tube 
    • Dobhoff tube
  • Central lines
  • Peripherally inserted central catheter
  • Swan-Ganz catheter
  • Chest tube

Lung anatomy

The following structures must be identified in a cephalocaudal manner and checked for abnormalities (e.g., cavitations, consolidations):

  • PA projection:
    • Right hemithorax:
      • Right upper lobe
      • Right lower lobe
      • Right costophrenic angle
      • Right cardiophrenic angle
    • Left hemothorax Hemothorax A hemothorax is a collection of blood in the pleural cavity. Hemothorax most commonly occurs due to damage to the intercostal arteries or from a lung laceration following chest trauma. Hemothorax can also occur as a complication of disease, or hemothorax may be spontaneous or iatrogenic. Hemothorax:
      • Left upper lobe
      • Left lower lobe
      • Left costophrenic angle
      • Left cardiophrenic angle
    • Trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea and carina
  • Lateral projection: 
    • The pulmonary lobes are identified by tracing a diagonal line and dividing the lung into:
      • An upper portion (2 upper lobes on the right, 1 upper lobe on the left)
      • A lower portion (1 lower lobe each on the right and left)

Heart and mediastinal anatomy

  • Mediastinum:
    • The area between the lungs and pleural cavities that stands in the middle of the thoracic cavity
    • Divided into the anterior, middle, and posterior mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels, this space houses every structure located medially to the lungs. 
    • This space contains:
      • Great vessels, such as the superior vena cava Superior vena cava The venous trunk which returns blood from the head, neck, upper extremities and chest. Mediastinum and Great Vessels (SVC), inferior vena cava Inferior vena cava The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels, pulmonary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries, pulmonary veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins, and the aorta
      • The thymus Thymus A single, unpaired primary lymphoid organ situated in the mediastinum, extending superiorly into the neck to the lower edge of the thyroid gland and inferiorly to the fourth costal cartilage. It is necessary for normal development of immunologic function early in life. By puberty, it begins to involute and much of the tissue is replaced by fat. Lymphatic Drainage System can be seen in the anterior mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels in children and young adults. 
  • The following structures must be identified in a cephalocaudal manner and checked for abnormalities in size or shape:
    • PA projection:
      • Trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea: should be on the midline
      • SVC
      • Ascending and descending aorta (aortic arch)
      • Pulmonary hilum (right and left)
      • Pulmonary artery
      • Right atrium (right heart border)
      • Left ventricle (left heart border)
    • To easily identify the structures on the left border in a cephalocaudal order, remember: 
      • 1st bump: aorta
      • 2nd bump: pulmonary artery
      • 3rd bump (largest): left ventricle
  • Lateral projection:
    • Retrosternal space
    • Right ventricle
    • Right hemidiaphragm
    • Aortic arch
    • Pulmonary hilum
    • Right atrium
    • Left ventricle
    • Left hemidiaphragm
    • Posterior cardiac space

Bones

The following structures must be identified in a cephalocaudal manner and checked for abnormalities (e.g., fractures):

  • PA projection:
    • Clavicles
    • Scapulae
    • Spinous processes of the vertebrae
  • Lateral projection: thoracic spine (evaluate vertebral body heights for compression fractures)
A pa projection of the chest identifying the major bony structures of the chest and the main structures of the upper abdomen

A posteroanterior projection of the chest identifying the major bony structures of the chest and the main structures of the upper abdomen

Image by Hetal Verma.

Upper abdomen

  • The clinician must be attentive for abnormal collections of air in this area.
  • The following parts of the upper abdomen are seen in a chest X-ray (PA and lateral projections):
    • Liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver
    • Stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach
    • Ascending, transverse, and descending colon

Abdomen and Pelvis

Abdominal X-rays have low sensitivity for evaluating solid organs, which is why they have been replaced by CT scans and ultrasound examination.

Projections

X-ray images of the abdomen can be produced in the following projections:

  • AP, also known by the acronym KUB ( kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys, ureters, and bladder):
    • Upright and supine
    • Paired with a PA projection of the chest in acute abdomen Acute Abdomen Acute abdomen, which is in many cases a surgical emergency, is the sudden onset of abdominal pain that may be caused by inflammation, infection, perforation, ischemia, or obstruction. The location of the pain, its characteristics, and associated symptoms (e.g., jaundice) are important tools that help narrow the differential diagnosis. Acute Abdomen
  • Lateral decubitus: used in patients who cannot stand up
  • Oblique: obtained when needed
Example of an abdominal x-ray

Abdominal X-ray showing an oval calculus projecting over the expected location of the right kidney/collecting system adjacent to the L3 transverse process

Image by Hetal Verma.

Sequence

The quality inspection of the image is done preferably before the reading sequence for abdominal X-rays:

  1. Lung bases 
  2. Free air
  3. Bowel-gas pattern
  4. Solid organs
  5. Soft-tissue masses
  6. Calcifications
  7. Bones

Bowel gas

  • The most radiolucent finding in the abdomen
  • The largest quantities are seen in the stomach and colon.
  • Small bowel:
    • Stacked-coin appearance
    • Large amounts of gas in the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine should be considered abnormal.
    • > 3 air-fluid levels in distended small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine indicative of functional ileus or mechanical obstruction
  • Large bowel:
    • Located in the periphery of the abdomen
    • The haustra separate gas into larger segments.
    • No air-fluid levels should be seen due to fluid absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption.
    • Stool is seen as small bubbles of gas in the expected trajectory of the colon.
  • Gas in the peritoneal cavity is indicative of post-operative status or pneumoperitoneum.

Soft tissues and fat shadow

  • Soft tissues:
    • The abdomen is occupied predominantly by soft tissue.
    • Liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver (RUQ)
    • Spleen Spleen The spleen is the largest lymphoid organ in the body, located in the LUQ of the abdomen, superior to the left kidney and posterior to the stomach at the level of the 9th-11th ribs just below the diaphragm. The spleen is highly vascular and acts as an important blood filter, cleansing the blood of pathogens and damaged erythrocytes. Spleen (LUQ)
  • Fat shadow:
    • Fat deposits delineate organs.
    • The flank stripe (properitoneal fat stripe) can be seen on the lateral abdominal walls.
      • The flank stripe can be identified by following the course of the ascending or descending colon.
      • Widening of the space between the stripe and the colon suggests the presence of fluid.

Bones

  • The most radiopaque finding in the abdomen
  • Ribs, lumbar and thoracic spines, and pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis
  • Calcifications (e.g., calcified arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries, urinary calculi, prostatic calculi, pancreatic calcifications)
Abdominal x-ray showing relevant structures

Abdominal X-ray with the relevant structures identified

Image by Hetal Verma.

Head and Spine

Imaging of the spine Imaging of the Spine The vertebral column and the spinal cord may be affected by various diseases, in which different imaging methods are important for correct diagnosis and management. Radiographs and CT scans are useful in evaluating bony structures, especially in excluding fractures and checking hardware. Imaging of the Spine and Spinal Cord and spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord using X-rays was widely used to study the contents of the cranial vault and the bones of the spine before the advent of CT and MRI.

Projections

  • X-ray images of the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull are produced in the following projections:
    • PA
    • Lateral
    • Waters’ view (occipitomental)
  • X-ray images of the spine are produced in the following projections:
    • AP
    • PA
    • Lateral 
    • Oblique 
    • The open-mouth (odontoid) view allows for visualization of the odontoid process of the axis (C2 vertebra).
    • Panoramic
Orbital x-ray (waters view)

Waters’ view of the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull:
This particular patient shows diffuse prominent mucosal thickening in the right maxillary sinus and mild mucosal thickening in the left maxillary sinus.

Image: “Orbital X-ray (Waters’ view)” by Erhan Erdogan, Vural Fidan, and Ersem Giritli. License: CC BY 4.0

Bones

  • In the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull, large quantities of X-rays are absorbed by the bones, making it difficult to visualize skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull contents and soft tissues.
  • Spinal structures:
    • Vertebral bodies
    • Facet joints
    • Disk spaces
    • Pedicles
    • Laminae
    • Transverse and spinous processes
    • Neural foramen
  • A panoramic view of the spine may be obtained, but the following visualizations are possible:
    • The thoracic spine using a chest X-ray
    • The lumbar spine using an abdominal X-ray

Spinal alignment

  • The spinous processes, pedicles, and laminae of the vertebrae must be checked for adequate positioning.
  • Vertebral lines should be parallel:
    • Anterior vertebral line: connects the anterior margins of the vertebral bodies
    • Posterior vertebral line: connects the posterior margins of the vertebral bodies
    • Spinolaminar line: connects the posterior margins of the spinal canal
    • Interspinous line: connects the tips of the spinous processes

Limbs and Joints

X-rays are used to assess the bones and joints of the extremities in suspected fractures, joint problems, and soft-tissue abnormalities ( inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation, edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema, or gas/emphysema, as seen in the cases of necrotizing fasciitis Necrotizing fasciitis Necrotizing fasciitis is a life-threatening infection that causes rapid destruction and necrosis of the fascia and subcutaneous tissues. Patients may present with significant pain out of proportion to the presenting symptoms and rapidly progressive erythema of the affected area. Necrotizing Fasciitis).

Projections

  • Specific projections to be requested depend on the bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones or joint to be studied. 
  • Commonly used projections include:
    • Frontal view
    • Lateral
    • Oblique: a frontal view with 15 degrees internal rotation (usually requested for the study of the ankle joint Ankle joint The ankle is a hinged synovial joint formed between the articular surfaces of the distal tibia, distal fibula, and talus. The ankle primarily allows plantar flexion and dorsiflexion of the foot. Ankle Joint)
  • Adequate imaging of bones and joints relies heavily on orthogonal imaging.

Joints

The following joints are commonly studied using conventional radiography:

  • Shoulder joint
  • Elbow joint Elbow joint The elbow is the synovial hinge joint between the humerus in the upper arm and the radius and ulna in the forearm. The elbow consists of 3 joints, which form a functional unit enclosed within a single articular capsule. The elbow is the link between the powerful motions of the shoulder and the intricate fine-motor function of the hand. Elbow Joint
  • Wrist joint Wrist joint The wrist connects the forearm to the hand. It consists of 8 carpal bones, multiple joints, and various supporting ligaments, as well as the distal bones of the forearm and the proximal portion of the 5 metacarpal bones of the hand. Wrist Joint
  • Sacroiliac joint
  • Hip joint Hip joint The hip joint is a ball-and-socket joint formed by the head of the femur and the acetabulum of the pelvis. The hip joint is the most stable joint in the body and is supported by a very strong capsule and several ligaments, allowing the joint to sustain forces that can be multiple times the total body weight. Hip Joint
  • Knee joint Knee joint The knee joint is made up of the articulations between the femur, tibia, and patella bones, and is one of the largest and most complex joints of the human body. The knee is classified as a synovial hinge joint, which primarily allows for flexion and extension with a more limited degree of translation and rotation. Knee Joint
  • Ankle joint

Fractures

The diagnosis of fractures can be made based on an X-ray of the affected limb or joint, usually utilizing 2 or more projections:

  • Clavicle fractures
  • Hip fractures Hip fractures A hip fracture is a disruption in the cortex of the femur at the hip joint, either between the trochanters (intertrochanteric) or at the femoral neck. Hip fracture is a serious injury and can result in life-threatening complications. Hip Fractures 
  • Distal radius fractures Distal radius fractures Distal radius fractures are one of the most common fractures encountered in practice and are often associated with falling onto an outstretched hand. These fractures are most frequently seen in older individuals, especially women. Distal Radius Fractures
  • Pelvic fracture Fracture A fracture is a disruption of the cortex of any bone and periosteum and is commonly due to mechanical stress after an injury or accident. Open fractures due to trauma can be a medical emergency. Fractures are frequently associated with automobile accidents, workplace injuries, and trauma. Overview of Bone Fractures
Ac separation xray (enhanced)

X-ray of a separated acromioclavicular joint (gray arrow)

Image: “AC Separation XRAY (enhanced)” by Root4(one). License: CC BY 2.5

Other Imaging Modalities

  • Imaging of the CNS (brain, spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord, and vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column): 
    • Radiography is often used to evaluate fractures of the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column
    • CT is a good choice to evaluate head trauma Head trauma Head trauma occurs when external forces are directed to the skull and brain structures, resulting in damage to the skull, brain, and intracranial structures. Head injuries can be classified as open (penetrating) or closed (blunt), and primary (from the initial trauma) or secondary (indirect brain injury), and range from mild to severe and life-threatening. Head Trauma and exclude intracranial hemorrhage.
    • MRI provides more detailed images of the brain and spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord, allowing for the identification of infarction, tumors, disc herniation, and demyelinating disease.
  • Pulmonary radiology Pulmonary Radiology Pulmonary, or chest, imaging includes imaging of the lungs and surrounding structures in the thorax. Imaging of the chest represents a substantial portion of the imaging tests that are routinely performed. Common imaging methods include X-ray, CT, MRI, and ultrasonography (US). Pulmonary Radiology and imaging of the mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels
    • Radiography is the preferred initial imaging study for viewing lung pathology. 
    • CT provides more detailed views of the lung parenchyma, mediastinal structures, and vasculature. 
    • Although MRI is not often used, it could be ordered for evaluating malignancies and cardiac disease.
    • Ultrasound can be used for the rapid assessment of bedside trauma and for guiding procedures (thoracentesis).
  • Breast imaging Breast Imaging Female breasts, made of glandular, adipose, and connective tissue, are hormone-sensitive organs that undergo changes along with the menstrual cycle and during pregnancy. Breasts may be affected by various diseases, in which different imaging methods are important to arrive at the correct diagnosis and management. Mammography is used for breast cancer screening and diagnostic evaluation of various breast-related symptoms. Breast Imaging
    • Mammography is often the initial choice to screen for breast cancer Breast cancer Breast cancer is a disease characterized by malignant transformation of the epithelial cells of the breast. Breast cancer is the most common form of cancer and 2nd most common cause of cancer-related death among women. Breast Cancer
    • MRI can be used to further evaluate and stage breast cancer Breast cancer Breast cancer is a disease characterized by malignant transformation of the epithelial cells of the breast. Breast cancer is the most common form of cancer and 2nd most common cause of cancer-related death among women. Breast Cancer
    • Ultrasound is helpful in evaluating lymph nodes and guiding biopsy.
  • Imaging of the abdomen and renal imaging Renal imaging The renal system is composed of 2 kidneys, 2 ureters, a bladder, and a urethra. Varying conditions such as infections, cysts, solid masses, ischemia, and mechanical obstruction can affect the renal system. Evaluation of diseases rely on imaging methods such as radiography, ultrasonography, CT, and MRI. Some of these are also used to guide tissue sampling (e.g., renal biopsy). Renal Imaging
    • Radiography is often used to evaluate for kidney stones, bowel obstruction, and pneumoperitoneum. In addition, barium may be used to assess swallowing and bowel function. 
    • CT and MRI provide more detailed assessments of the abdominal viscera and vasculature. 
    • Nuclear medicine can be used to assess gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract function, gastric emptying, and GI bleeding.
  • Imaging of the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Posterior Abdominal Wall and ovaries Ovaries Ovaries are the paired gonads of the female reproductive system that contain haploid gametes known as oocytes. The ovaries are located intraperitoneally in the pelvis, just posterior to the broad ligament, and are connected to the pelvic sidewall and to the uterus by ligaments. These organs function to secrete hormones (estrogen and progesterone) and to produce the female germ cells (oocytes). Ovaries
    • Ultrasound is the most commonly used modality to evaluate the ovaries Ovaries Ovaries are the paired gonads of the female reproductive system that contain haploid gametes known as oocytes. The ovaries are located intraperitoneally in the pelvis, just posterior to the broad ligament, and are connected to the pelvic sidewall and to the uterus by ligaments. These organs function to secrete hormones (estrogen and progesterone) and to produce the female germ cells (oocytes). Ovaries and uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Posterior Abdominal Wall, including pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-HCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care assessment and determining the causes of abnormal uterine bleeding Abnormal Uterine Bleeding Abnormal uterine bleeding is the medical term for abnormalities in the frequency, volume, duration, and regularity of the menstrual cycle. Abnormal uterine bleeding is classified using the acronym PALM-COEIN, with PALM representing the structural causes and COEIN indicating the non-structural causes. Abnormal Uterine Bleeding
    • CT and MRI provide more detailed views and are often useful in assessing cysts, malignancies, and benign masses.
  • Imaging of the musculoskeletal system: 
    • Radiography is often used to exclude fractures. 
    • CT is more sensitive to bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones pathology, including osteomyelitis Osteomyelitis Osteomyelitis is an infection of the bone that results from the spread of microorganisms from the blood (hematogenous), nearby infected tissue, or open wounds (non-hematogenous). Infections are most commonly caused by Staphylococcus aureus. Osteomyelitis
    • MRI is preferred for soft-tissue evaluation, such as assessing for malignancy and myositis. 
    • Bone scan can be useful in determining occult fractures, osteomyelitis Osteomyelitis Osteomyelitis is an infection of the bone that results from the spread of microorganisms from the blood (hematogenous), nearby infected tissue, or open wounds (non-hematogenous). Infections are most commonly caused by Staphylococcus aureus. Osteomyelitis, and metabolic bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones disease.

References

  1. Berger, M., Yang, Q., Maier, A. (2018). X-ray Imaging. In: Maier, A., Steidl, S., Christlein, V., et al., Editors. Medical Imaging Systems: An Introductory Guide [Internet]. Cham (CH): Springer. https://www.ncbi.nlm.nih.gov/books/NBK546155/
  2. Chen, M.M. (2011). Chapter 8. Plain film of the abdomen. Chen, M.M., Pope, T.L., Ott, D.J. (Eds.), Basic Radiology, 2e. McGraw-Hill. https://accessmedicine-mhmedical-com.ezproxy.unbosque.edu.co/content.aspx?bookid=360&sectionid=39669017
  3. Dixon, R.L., Whitlow, C.T. (2011). Chapter 2. The physical basis of diagnostic imaging. In Chen, M.Y.M., Pope, T.L., Ott, D.J. (Eds.), Basic Radiology, 2e. New York, NY: The McGraw-Hill Companies. accessmedicine.mhmedical.com/content.aspx?aid=6668091
  4. Guha-Thakurta, N., & Ginsberg, L.E. (2011). Chapter 13. Imaging of the spine. Chen, M.M., Pope, T.L., Ott, D.J. (Eds.), Basic Radiology, 2e. McGraw-Hill. https://accessmedicine-mhmedical-com.ezproxy.unbosque.edu.co/content.aspx?bookid=360&sectionid=39669023
  5. Miner Haygood, T., Sayyouh, M.H. (2011). Chapter 6. Musculoskeletal imaging. Chen, M.M., Pope, T.L., Ott D.J. (Eds.), Basic Radiology, 2e. McGraw-Hill. https://accessmedicine-mhmedical-com.ezproxy.unbosque.edu.co/content.aspx?bookid=360&sectionid=39669014
  6. Wasserman, P.L., Pope, T.L. (2011). Chapter 7. Imaging of joints. Chen, M.M., Pope T.L., Ott D.J. (Eds.), Basic Radiology, 2e. McGraw-Hill. https://accessmedicine-mhmedical-com.ezproxy.unbosque.edu.co/content.aspx?bookid=360&sectionid=39669015
  7. Zaer, N.F., Amini, B., Elsayes, K.M. (2015). Overview of diagnostic modalities and contrast agents. In Elsayes, K.M., Oldham, S.A.A. (Eds.), Introduction to diagnostic radiology. New York, NY: McGraw-Hill Education. Retrieved from accessmedicine.mhmedical.com/content.aspx?aid=1115257266
  8. Zapadka, M.E., Bradbury, M.S., Williams, D.W. III. (2011). Chapter 12. Brain and its coverings. Chen, M.M., Pope, T.L., Ott, D.J. (Eds.), Basic Radiology, 2e. McGraw-Hill. https://accessmedicine-mhmedical-com.ezproxy.unbosque.edu.co/content.aspx?bookid=360&sectionid=39669022
  9. CDC. (2020). Radiation and Pregnancy: A Fact Sheet for Clinicians. Retrieved April 19, 2021, from https://www.cdc.gov/nceh/radiation/emergencies/prenatalphysician.htm

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