Nuclear Medicine: Bone, Cardiac and Thyroid Scan

00:01 So let's move on and discuss bone scans.

00:03 Bone scans are very commonly performed.

00:06 The radioisotope that's used is Technetium-99m again, and the pharmaceutical is Methylene diphosphonate or MDP.

00:15 The images are usually obtained about four hours after injection which allows them to take, which allows the radiotracer to be taken up into the bones.

00:24 So bone scans are really the best methods for screening for bony metastases.

00:29 It's the most sensitive to evaluate for fractures that are also not visualized on radiography.

00:34 So usually when a patient comes in for fracture, the first modality would be a plain film to see if we can see the fracture.

00:39 If not, then the next step could be a bone scan which would provide a very sensitive evaluation for a fracture.

00:45 However, it's not very specific.

00:47 So anything such as a fracture, degenerative changes, metastases or even osteomyelitis will produce increased uptake and so when you see increased uptake on a bone scan, it's hard for us to differentiate what maybe going on.

00:59 And the clinical scenario has really need to be taken into account.

01:02 So metastases appear as multiple asymmetric areas of increased uptake.

01:09 Radiotracer is taken up by areas of greatest bone turnover and so blastic metastases for this reason, demonstrate increased uptake.

01:17 However if you have a pure lytic metastases, that may be missed because you don't have a lot of bone turnover in a purely lytic metastases.

01:25 So this is an example of a normal bone scan.

01:30 Usually we have anterior and posterior images obtained to take a better look at all of the structures.

01:35 And you can see here that there's symmetric uptake in the visualized bony structures.

01:40 So you have the shoulders here, which have symmetrical, bilateral uptake.

01:43 You have normal uptake within the spine.

01:46 And then you have symmetric uptake within both lower extremities here as well as both upper extremities here.

01:53 Somewhat prominent uptake within the skull is also expected and that's normal.

01:59 And then focus down here is your urinary bladder because of excretion of radiotracer into the bladder.

02:06 Just as a note, this patient actually has a slight lumbar spine scoliosis which you can see right here as a turning of the spine.

02:13 So let's take a look at this bone scan.

02:17 How does this look different from the one that we just saw? So you can actually see here multiple asymmetric areas of uptake within the ribs, you have multiple areas within the ribs right here which asymmetric from the other side.

02:37 You have areas of increased uptake within the pelvis.

02:40 So this area right here stands out much more significantly than the area on the right side over here.

02:47 You also have asymmetric uptake within the shoulder.

02:49 So the right shoulder has more uptake than the left shoulder does.

02:54 This patient actually has metastatic breast carcinoma and this was known prior to performing the bone scan so that we know these areas of uptake are related to bony metastases.

03:04 Cardiac scans are also very commonly performed as a nuclear medicine examination.

03:12 It's also called a myocardial perfusion scan or myocardial perfusion imaging and the radiopharmaceuticals that are used can be multiple.

03:21 Two of them are Technitium-99 labelled or we can also use Thallium 201.

03:27 So what are the indication for cardiac imaging? It can be used to evaluate for myocardial ischemia or infarction.

03:35 It can also be used to detect wall motion abnormalities because again you have to remember that nuclear medicine is the physiologic functional examination.

03:43 We can use myocardial perfusion imaging to calculate left ventricular ejection fraction as well.

03:49 So cardiac images are obtained at both stress and rest and the two are then compared.

03:55 So the stress is can be performed in a couple of different ways.

03:58 It can be exercise induced such are running on a treadmill.

04:02 However for patients that can't exercise it can also be pharmacologic.

04:06 So the patient can be given Adenosine, dobutamine or dipyridamole prior to the examination, the stress portion of the examination.

04:13 This is an example of a normal cardiac scan.

04:18 So images are obtained in three different planes.

04:21 We have short access. We have horizontal long access and then we have vertical long access.

04:26 The top row of images shows the exam performed under cardiac stress and then the bottom row of each set is performed at rest.

04:36 So we have short access stress, short access rest.

04:40 And then we have horizontal long access stress, horizontal long access rest and this is the vertical long access stress and vertical long access rest.

04:50 And then again, these are all compared.

04:53 So let's take a look at the scan here.

04:55 See how it differs from the prior one that we looked at.

04:57 On these images, again let's take a look at this row here.

05:01 This is the horizontal long access and these up here are the stress images.

05:05 These down here are the rest images.

05:08 So in the normal heart, the stress and rest images should have normal flow to all aspects of the heart. It should be the same at both stress and rest.

05:17 However, if you look at these stress images here, you can see an area of photopenia which isn't present on the rest images.

05:25 So under stress this heart is losing blood flow to this portion.

05:29 So this is called a defect on the stress portion of the images and it improves on rest which is consistent with ischemia.

05:37 If the defect persists on both the rest and stress images, then that represents an infarction.

05:43 So you can also perform EKG gated SPECT images.

05:49 EKG gating refers to the technique of acquiring images based on the EKG rhythm.

05:53 So the images are obtained at the same point in the cardiac cycle each time.

05:58 This allows for evaluation of wall motion abnormalities.

06:01 And this can also be performed as one of the ways of performing a cardiac scan.

06:05 So let's move on to Thyroid scans.

06:09 The radiopharmaceutical that's used for thyroid scans can either be radioactive iodine or Technetium-99 pertechnetate.

06:19 Thyroid scans are used to perform the function, to look at the functionality of nodules and the functionality of the entire thyroid glands.

06:28 There can be cold nodules or there can be hot nodules.

06:32 Cold nodules are those that demonstrate decreased uptake so the rest of the gland has normal uptake but the cold nodule has less uptake than the rest of the gland.

06:41 Hot nodules demonstrate increased uptake from the rest of the gland.

06:44 So nodules are actually a very common finding and they're often evaluated even on ultrasound.

06:50 However, the functionality can only be assessed on a thyroid scan.

06:54 Majority of the nodules are benign and solitary cold nodules are actually more likely to represent a carcinoma than hot nodules are.

07:03 Nodules can also be evaluated by ultrasound and if sampling is needed, they can be sampled using ultrasound guided fine needle aspiration.

07:11 So this is an example of a normal thyroid scan.

07:17 And this is compared. So this is the normal right here.

07:20 And this is compared with an abnormal scan on this side.

07:24 So you can see normal, symmetric uptake within the thyroid gland on the normal scan. You don't see any areas that appear photopenic and you don't see any areas that appear bright.

07:33 However, on the scan on the right you can see two different areas.

07:37 This one right here, in the lower lobe on the right which demonstrates a hot nodule and in the left upper lobe we actually have an area of photopenia which is an example of a cold nodule.

07:48 So in this patient the next step would probably be to perform an ultrasound and then depending on what that looks like, the patient likely needs an ultrasound guided fine needle aspiration of the cold nodule that's in the left upper lobe.

08:00 Radioactive thyroid ablation can also be performed by nuclear medicine radiologist.

08:08 It actually requires significantly higher doses of radioactive iodine.

08:12 I-131 is the one that's used. And that can ablate the gland.

08:15 And this is done in patients that have either Grave's disease or thyroid carcinoma.

08:19 So in this lecture we've reviewed nuclear medicine in general.

08:25 How it's different than the rest of radiology.

08:27 And how it represents more functional or physiologic imaging than the rest of radiology does.

08:31 And we've gone over some very common nuclear medicine examinations and gone over some abnormal findings that can be seen in each one.