Terminology and Technological Aspects
Mechanism
- Nuclear medicine differs from the rest of radiology because it involves functional rather than structural imaging.
- Radioisotopes: unstable forms of an element that emit detectable particles as they decay into more stable forms
- Radiopharmaceuticals:
- Artificially produced isotopes bound to pharmaceuticals (radioisotope + an organic molecule)
- Administered to patients and used in nuclear medicine
- The organic molecule allows isotopes to concentrate within a specific target organ.
- The radioisotope emits detectable ionizing radiation (high-energy rays) when it decays, which is visualized during imaging.
Image creation
Equipment:
- The machine is equipped with a gamma camera that detects radiation and forms an image.
- Components of the gamma camera:
- Collimator: 1st layer between the patient and the crystal. The collimator is made of lead with holes to reduce scatter.
- Crystal: emits faint light after interacting with gamma rays
- Photomultiplier tubes: detect and convert light from the crystal into electrical signals
- Electronics for processing data: analyze signals and produce viewable images
Imaging techniques:
- Single-photon emission computed tomography (SPECT):
- Uses gamma-emitting radioisotopes
- A 3D nuclear imaging made by multiple 2D images acquired at different angles
- PET:
- Uses positron-emitting radioisotopes
- Superior image quality (contrast and resolution) but more expensive
- Combined imaging techniques:
- CT (PET-CT or SPECT-CT) or MRI is integrated.
- Improved localization of lesions
A SPECT/CT system with relevant components labeled in the photograph on the right
Image: “NM19 290” by Kieran Maher. License: Public DomainCommon nuclear medicine exams
- Hepatobiliary iminodiacetic acid (HIDA) scan
- Ventilation and perfusion (VQ) scan
- 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 scan
- Cardiac scan
- Thyroid scan
Hepatobiliary Iminodiacetic Acid Scan
- HIDA scan (cholescintigraphy):
- Examination of the 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
- The radiopharmaceutical is normally taken up by the 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 and excreted through the biliary system as bile.
- Radiopharmaceutical: technetium-99m iminodiacetic acid
- Isotope: technetium-99m
- Indications:
- Acute cholecystitis Cholecystitis Cholecystitis is the inflammation of the gallbladder (GB) usually caused by the obstruction of the cystic duct (acute cholecystitis). Mechanical irritation by gallstones can also produce chronic GB inflammation. Cholecystitis is one of the most common complications of cholelithiasis but inflammation without gallstones can occur in a minority of patients. Cholecystitis with equivocal ultrasound findings
- Biliary atresia
- Biliary leak
- Biliary dyskinesia: Cholecystokinin is administered and 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 ejection fraction is calculated.
- Contraindication: allergy to the radiotracer (anaphylaxis)
| Imaging finding | Interpretation |
|---|---|
| Bile ducts visible | Normal hepatic function |
| Filling of the 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 | Patent cystic duct |
| Radiotracer is seen in the duodenum | Patent common bile duct common bile duct The largest bile duct. It is formed by the junction of the cystic duct and the common hepatic duct. Acute Cholangitis |
| No radiotracer is seen in the 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 | Obstructed 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 (acute cholecystitis Cholecystitis Cholecystitis is the inflammation of the gallbladder (GB) usually caused by the obstruction of the cystic duct (acute cholecystitis). Mechanical irritation by gallstones can also produce chronic GB inflammation. Cholecystitis is one of the most common complications of cholelithiasis but inflammation without gallstones can occur in a minority of patients. Cholecystitis) |
| No radiotracer is seen in the duodenum | Biliary atresia |
| Radiotracer outside the biliary system | Biliary leak |
Hepatobiliary iminodiacetic acid scan
Image by Lecturio.
Normal hepatobiliary iminodiacetic acid scan showing the radioactive substance moving through the biliary system
Image: “HIDA” by Myohan. License: CC BY 3.0
Hepatobiliary iminodiacetic acid scan in a patient with 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 pathology:
Image: “Acute 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 torsion – a continued pre-operative diagnostic dilemma” by Mouawad NJ, Crofts B, Streu R, Desrochers R, Kimball BC. License: CC BY 2.0
Demonstration of uptake of tracer in 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 without visualization of the 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. Delayed images show excretion of tracer into the small bowel.
(a) Cholescintigraphy anterior view: left: 52–56 min after tracer injection; middle: 2 hours after tracer injection; right: 5 hours after tracer injection. Biliary atresia (BA) was suspected and the patient was referred for a technetium-99m trimethyl bromo-iminodiacetic acid hepatobiliary scintigraphy (99mTc-mebrofenin hepatobiliary scintigraphy), which showed rapid extraction of tracer by the 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 with no excretion to the small bowel but with suspicion of visualization of the 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 (thick black arrows). The tracer was physiologically excreted in the urine and localized in a diaper (white arrow).
Image: “Potential Pitfalls on the (99m)Tc-Mebrofenin Hepatobiliary Scintigraphy in a Patient With Biliary Atresia Splenic Malformation Syndrome” by Maestri Brittain J, Borgwardt L. License: CC BY 4.0
(b) MRI, coronal view (T2 weighted), demonstrating that the 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 is separated into several lobes, indicating a false positive on the hepatobiliary iminodiacetic acid scan for 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 visualization. This was a confirmed case of biliary atresia.
Ventilation and Perfusion Scan
- Phases:
- Ventilation phase:
- The patient breathes in the radiopharmaceutical, typically Xenon-133, in the form of an aerosol (other option: technetium-99m diethylenetriaminepentaacetate (DTPA)).
- Small particles then are deposited into the alveoli and images are acquired.
- Perfusion phase:
- An injectable radiopharmaceutical (technetium-99m macroaggregated albumin (MAA)) is administered.
- Technetium-99m MAA enters the pulmonary vessels and images are acquired.
- Ventilation phase:
- Indications:
- For evaluation of
pulmonary embolism
Pulmonary Embolism
Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs.
Pulmonary Embolism when CT pulmonary angiography is contraindicated:
- IV contrast allergy
- 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
- Renal failure
- Preoperative estimates of lung function: preparation for surgical excision
- For evaluation of
pulmonary embolism
Pulmonary Embolism
Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs.
Pulmonary Embolism when CT pulmonary angiography is contraindicated:
- Contraindication: allergy to radiotracers (anaphylaxis)
- Normal VQ scan findings:
- Normal perfusion: uniform uptake in the 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 with areas of photopenia in the region of the heart and hila
- Normal ventilation: radiotracer homogeneously washing into the lung with quick washout and no evidence of air trapping
- Always obtain a chest radiograph prior to a VQ scan to exclude consolidation, which gives a false-positive result.
| Category | Findings |
|---|---|
| High 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 pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism | More than 2 large mismatched segmental defects |
| Intermediate 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 pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism |
|
| Low 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 for pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism |
|
| Normal | No matched or mismatched defects |
Normal pulmonary ventilation and perfusion (VQ) scan. The nuclear medicine VQ scan is useful in the evaluation of pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism.
Image: “Ventperf” by Myohan. License: CC BY 3.0
High 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 for pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism:
Image: “Pulmonary embolism presenting as syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope: A case report” by Demircan A, Aygencel G, Keles A, Ozsoylar O, Bildik F. License: CC BY 3.0
Decreased perfusion is seen to the right lung and is particularly evident in the right lower lobe on the right posterior oblique (RPO) image (perfusion scan was performed using Tc-99m macroaggregated albumin).
High 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 for pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism:
Image: “Pulmonary embolism presenting as syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope: A case report” by Demircan A, Aygencel G, Keles A, Ozsoylar O, Bildik F. License: CC BY 3.0
No significant ventilation defect (ventilation scan performed using Xe-133 gas)
High 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 for pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism:
Image: “Pulmonary embolism scintigraphy PLoS” by Westgate EJ, FitzGerald GA. License: CC BY 2.0
Ventilation-perfusion scintigraphy in a woman taking oral contraceptives and valdecoxib
A: Ventilation phase: uniform ventilation to 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
B: Perfusion phase: This and other views show decreased activity in the apical segment of right upper lobe, anterior segment of right upper lobe, superior segment of right lower lobe, posterior basal segment of right lower lobe, anteromedial basal segment of left lower lobe, and lateral basal segment of left lower lobe.
Bone Scan
- The skeletal system can be assessed using nuclear medicine.
- The radiopharmaceutical that is used chemoadsorbs to the hydroxyapatite crystals in the bone matrix; thus, areas of bone turnover can be identified.
- Increased bone turnover is seen in fractures, tumors, and acute infection.
- Isotope: technetium-99m
- Radiopharmaceutical: methylene diphosphonate
- Imaging:
- Images are obtained 4 hours after injection, allowing the radiotracer to be taken up by the bone.
- Anterior and posterior images are obtained.
- Indications:
- Bony metastases screening
- Evaluation of fractures (e.g., stress 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) that are not visible on a radiograph
- Infections
| Results | Description | Accuracy | Examples |
|---|---|---|---|
| Normal |
|
True negative | False negative |
| Normal skeleton | Purely lytic metastasis | ||
| Abnormal | Asymmetric increased uptake | True positive | False positive |
|
|
Normal bone scan with 2 views and no asymmetric increased uptake
Image: “Nl bone scan2” by Myohan. License: CC BY 3.0
A: 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 scintigraphy during interferon-α treatment: Multiple bone metastases are visible (red arrows).
Image: “Long-term survival following multidisciplinary treatment of metastatic sarcomatoid renal cell carcinoma Renal cell carcinoma Renal cell carcinoma (RCC) is a tumor that arises from the lining of the renal tubular system within the renal cortex. Renal cell carcinoma is responsible for 80%-85% of all primary renal neoplasms. Most RCCs arise sporadically, but smoking, hypertension, and obesity are linked to its development. Renal Cell Carcinoma: A case report” by Yaegashi H, Izumi K, Konaka H, Mizokami A, Namiki M. License: CC BY 4.0
B: 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 scintigraphy at present state: Abnormal accumulations are less visible.
Oval-shaped increased osteoblastic activity on the metaphyseal region of both tibias (arrows) (stress fractures due to marathon running)
Image: “Stress 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 of bilateral tibial metaphysis due to ceremonial march training: A case report” by Kurklu M, Ozboluk S, Kilic E, Tatar O, Ozkan H, Basbozkurt M. License: CC BY 2.0
Cardiac Scan
- Also known as myocardial perfusion imaging
- Detects variation in blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure and myocardial extraction of radiotracers
- Materials:
- Isotopes:
- Technetium-99m
- Thallium-201
- Radiopharmaceuticals:
- Sestamibi
- Teboroxime
- Isotopes:
- Procedure:
- In normal coronary 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, significant arterial dilatation is seen in response to exercise/stress.
- Stenotic areas do not show dilatation; thus, ischemia and ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) changes occur.
- In a cardiac scan, stress is either:
- Induced by exercise by running on a treadmill
- Pharmacologically induced by giving adenosine or dobutamine to those who cannot run
- Imaging is obtained at both stress and rest.
- Radiopharmaceuticals are injected when 85% of the maximum predicted heart rate (MPHR) is reached.
- Indications:
- Myocardial ischemia or infarction evaluation
- Wall-motion abnormalities: performed using ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG)-gated SPECT scan
- Calculate left ventricular ejection fraction
- Normal cardiac scan obtained in 3 different planes:
- The top row of each set is performed under cardiac stress.
- Bottom row of each set is performed at rest.
- Normal flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure to all aspects of the heart at both rest and stress
- Abnormal cardiac scans:
- Myocardial ischemia: areas of photopenia (i.e., decreased uptake) under stress, which improve at rest
- Myocardial infarction Myocardial infarction MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction: persistent photopenia (i.e., decreased uptake) despite rest state
Normal myocardial perfusion scan with thallium-201 for the rest images (bottom rows) and technetium-sestamibi for the stress images (top rows)
Image: “Nl mpi2” by Myohan. License: CC BY 3.0
A patient with multiple perfusion defects with different degrees of severity.
Image: “Frequency and severity of myocardial perfusion abnormalities using Tc-99m MIBI SPECT in cardiac syndrome X” by Saghari, M. et al. License: CC BY 2.0
The upper images are stress phase and lower images are rest or delayed images. There is moderate ischemia in the mid anterolateral and mid inferolateral walls.
There also is severe ischemia in the basal inferior wall. Mild ischemia in the apex, apical septal, and basal anterolateral regions are also noted.
Thyroid Scan
- The thyroid gland Thyroid gland The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland transports iodine; thus, radioiodine is used to detect the function of the whole gland or nodules.
- Radiopharmaceuticals:
- Radioactive iodine (iodine-123)
- Technetium-99 pertechnetate
- Indications:
- Thyroid nodules Thyroid nodules A thyroid nodule is a disordered growth of thyroid cells that produces a mass in the thyroid gland. Most thyroid nodules are benign and detected either by the patient or by the clinician on examination. In other cases, a thyroid nodule is found in radiologic imaging incidentally. Ruling out of malignancy is important. Thyroid Nodules
- Patients with thyrotoxicosis Thyrotoxicosis Thyrotoxicosis refers to the classic physiologic manifestations of excess thyroid hormones and is not synonymous with hyperthyroidism, which is caused by sustained overproduction and release of T3 and/or T4. Graves' disease is the most common cause of primary hyperthyroidism, followed by toxic multinodular goiter and toxic adenoma. Thyrotoxicosis and Hyperthyroidism
- Patients with
thyroid cancer
Thyroid cancer
Thyroid cancer is a malignancy arising from the thyroid gland cells: thyroid follicular cells (papillary, follicular, and anaplastic carcinomas) and calcitonin-producing C cells (medullary carcinomas). Rare cancers are derived from the lymphocytes (lymphoma) and/or stromal and vascular elements (sarcoma).
Thyroid Cancer:
- Distant metastasis (whole body scan)
- Local residual disease
- Therapeutic use: radioactive thyroid ablation (in Graves’ disease or thyroid carcinoma) using higher doses of radioactive iodine (iodine-131 destroys thyroid cells)
- Contraindications:
- 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
- Lactation
| Uptake | Pattern | Diagnosis |
|---|---|---|
| Increased | Nodular (hot nodule) | Toxic adenoma |
| Diffuse | Graves’ disease | |
| Normal | Symmetric uptake with no defects | |
| Decreased | Nodular (cold nodule) | Thyroid cancer |
| Diffuse | Hashimoto thyroiditis Thyroiditis Thyroiditis is a catchall term used to describe a variety of conditions that have inflammation of the thyroid gland in common. It includes pathologies that cause an acute illness with severe thyroid pain (e.g., subacute thyroiditis and infectious thyroiditis) as well as conditions in which there is no clinically evident inflammation and the manifestations primarily reflect thyroid dysfunction or a goiter (e.g., painless thyroiditis and fibrous Riedel's thyroiditis). Thyroiditis |
Normal thyroid scan
Image: “Thyroid scan” by Myohan. License: CC BY 3.0
Technetium-99 pertechnetate (99mTcO4) thyroid scan:
Image: “Thyroid Nodule Imaging, Status and Limitations” by Asia Oceania Journal of Nuclear Medicine & Biology (2015). License: CC BY 3.0
A: A large hot nodule with suppression of the rest of the thyroid
B: A large cold nodule in the left lobe of the thyroid
On cytology, the hot nodule was reported as a “follicular neoplasm” and the cold nodule was reported as a “colloid nodule.”
Initial thyroid ultrasound scanning and 99m-Technetium scintiscan
Image: “Localized subacute thyroiditis Thyroiditis Thyroiditis is a catchall term used to describe a variety of conditions that have inflammation of the thyroid gland in common. It includes pathologies that cause an acute illness with severe thyroid pain (e.g., subacute thyroiditis and infectious thyroiditis) as well as conditions in which there is no clinically evident inflammation and the manifestations primarily reflect thyroid dysfunction or a goiter (e.g., painless thyroiditis and fibrous Riedel's thyroiditis). Thyroiditis presenting as a painful hot nodule” by Li LX, Wu X, Hu B, Zhang HZ, Lu HK. License: CC BY 2.0
A: Thyroid ultrasonography reveals an ill-defined, solid, hypoechoic nodule (15 × 0.8 mm) with an irregular border in the left thyroid lobe (indicated by a white arrow).
B: Thyroid scintigraphy with 99m-Tc shows focal accumulation of radiotracer uptake in the lower lobe of the left thyroid, which represents the palpable tender nodule (indicated by a black arrow).
Other Imaging Modalities by System
- 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 determine 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 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.
- MRI is not often used, but may be employed for evaluating malignancies and cardiac disease.
- Ultrasound can be used for rapid bedside-trauma assessment 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 for breast cancer screening Breast cancer screening Breast cancer is the most common cancer in women and the 2nd-leading cause of cancer-related deaths in women in the United States. Early detection and improved pathology-specific treatments have resulted in a decrease in death rates. Breast Cancer Screening.
- MRI can be used to further evaluate and stage breast cancers.
- Ultrasound is helpful in the evaluation of lymph nodes and in 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 ovary 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 assessing pregnancies and determining the cause 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 pathology, including osteomyelitis.
- MRI is preferred for soft-tissue evaluation, such as assessing for malignancy and myositis.
- 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 scan can be useful in determining occult fractures, osteomyelitis, and metabolic bone disease.
References
- Brandon, D.C., Thomas, A.J., Ravizzini, G.C. (2014). Introduction to nuclear medicine. https://accessmedicine.mhmedical.com/content.aspx?bookid=1562§ionid=95875470
- Elsayes, K.M., Oldham, S.A. (Eds.) (2014). Introduction to Diagnostic Radiology. McGraw-Hill.
- Chen, M.M., Whitlow, C.T. (2011). Chapter 1. Scope of Diagnostic Imaging. In Chen M.M., Pope T.L., Ott D.J.(Eds.). Basic Radiology, 2e. McGraw-Hill.
