Nuclear Medicine: Name That Scan Part 1

Radiology board review with questions, answers, and tips to correctly identify nuclear medicine scans based simply on imaging appearance and distribution of uptake.  

Radiology board review with questions, answers, and tips to correctly identify nuclear medicine scans based simply on imaging appearance and distribution of uptake.   For those looking for additional help with the ABR Core Exam, check out this community of residents, fellows, and radiology faculty created to help R3s and R4s get ready for radiology board exams during this time when people can't study in person.

Show Notes/Study Guide:

What are some basic ways to tell between a general nuclear medicine scan (using gamma cameras) and a PET scan?

PET scans are higher quality, a maximal intensity projection (MIP) image means you are looking at a PET scan, a planar image means you are looking at a general nuclear medicine (gamma camera) scan. Note that fused images can be SPECT/CT or PET/CT (or PET/MR) and the fusion alone does not mean it is a PET scan.

What type of general nuclear medicine scan is characteristic on board exams for having a super-hot spleen?

Tagged white blood cell scan.  Note that tagged WBC scans can be Tc or In111.  Tc may be preferred in kids (shorter half-life—lower dose and higher quality imaging of smaller anatomy). In111 offers advantage of more delayed imaging and less bowel uptake (indium WBC scan best for inflammatory bowel disease evaluation).  An octreotide scan can also have really hot spleen but generally has more counts (looks like a higher quality study) and also has robust kidney uptake without bone uptake.  If they show you tagged In111 WBC scan with really hot kidneys you should consider pyelonephritis or causes of renal inflammation that may include recent chemotherapy. 

Tc WBC scan: 4 and 24 hour imaging common, has renal and GI activity.  Lungs hot on 4 hour imaging, GI tract hot on 24 hour imaging.

In111 WBC scan: No renal and no GI activity for contamination, lower count study (due to longer half-life and lower injected doses, also less optimal energies for gamma camera imaging).

For whole body iodine scans with I131 or I123 what is the expected uptake in the liver, in the heart, and in the bones/marrow?

I131 and I123 scans are not expected to have uptake in the heart, kidneys or bones/marrow.  Liver uptake is not present normally on a pre-treatment iodine body search but can be seen on a post-therapy scan. See here for more info: https://pubmed.ncbi.nlm.nih.gov/9255147/ You can have some slight gastric and bowel uptake with salivary secretion of iodine and normal nasopharyngeal uptake.  Of course, you expect thyroid uptake and uptake in any potential thyroid cancer metastases.

Bonus: What is the next step if you see a negative whole body Iodine scan in a patient with history of thyroid cancer with a rising, elevated thyroglobulin level? 

Get an FDG-PET/CT scan.  Concern for de-differentiated thyroid cancer that no longer takes up iodine but would then be expected to be aggressive and glucose hungry—thus FDG avid.