1.5 Introduction to Nuclear Medicine Flashcards
Describe the general mechanism of acquisition for nuclear medicine imaging.
Patient is given a radiopharmaceutical, which is a radioisotope (unstable form of a compound which releases radiation to become a more stable form) bonded to a pharmaceutical which causes it to bond to specific organ tissues.
Gamma decay occurs when the unstable nucleus emits electromagnetic radiation to reach a more stable form. This radiation is picked up by a gamma camera, which measures it and forms an image.
The image is usually poor resolution, e.g. 1 cm and can be static or dynamic.
What is the major difference in purpose for nuclear imaging compared to other forms of imaging?
Nuclear imaging examines organ function**, whereas other forms of imaging examine organ **anatomy.
What is SPECT imaging?
A type of nuclear imaging.
SPECT - single photon emitted CT (computed tomography)
Multiple 2D images taken to create a 3D image.
Name 5 common forms of nuclear imaging (high yield).
- HIDA scan
- V/Q scan
- Bone scan
- Cardiac scan
- Thyroid scan
What is a HIDA scan and how does it work?
Explain the mechanism of acquisition.
HIDA scan stands for hepatobiliary iminodiacetic acid and is also known as a cholescintography.
It uses:
- Radioisotope - Technetium-99
- Radiopharmaceutical - Iminodiacetic Acid
IDA binds to protein and is taken up by the liver and excreted with the bile.
It is used to highlight hepatic, biliary, gallbladder and duodenal structures.
What is the indication for a HIDA scan?
It is to look for cholecystitis.
Describe the structures highlighted at different time-points in a HIDA scan.
Describe the normal HIDA vs. the ‘cholecystitic’ HIDA.
What is the indication for a V/Q scan?
What imaging modality should always precede a V/Q scan, where possible?
[High Yield]
CTPA is the gold standard for detection of pulmonary embolism.
However, patients with contraindications to CTPA, e.g. anaphylaxis to contrast, pregnancy should have a V/Q scan instead.
A CXR should precede a V/Q scan where possible, as you need to exclude consolidation which can result in a false positive.
Describe the mechanism of image acquisition in a V/Q scan.
There are 2 parts of the scan, one part which checks lung ventilation, one part that checks lung perfusion.
Radio-isotope: Technetium-99
Radio-pharmaceutical:
- Ventilation: Aerosol, such as xenon or krypton
- Perfusion: Microaggregated albumin (MAA) which is injected into the vein.
During the scan, the patient is injected IV with MAA and breathes in the gas, both of which are labelled with Technetium-99.
The images captured are compared to see if there is a ventilation/perfusion mismatch.
The images are then ranked ‘Normal’, ‘Low’, ‘Intermediate’ and ‘High’ based on how likely it is that the patient has a pulmonary embolus.
How are V/Q scan images ranked?
The images are ranked ‘Normal’, ‘Low’, ‘Intermediate’ and ‘High’ based on how likely it is that the patient has a pulmonary embolus.
These are based on findings from the PIOPED study (Prospective Investigation of Pulmonary Embolism Diagnosis study).
The number and size of mismatches are used to calculate probability.
Describe what findings would be present in a V/Q scan with a mismatch.
Ventilation would be normal, whereas there would be a large defect in perfusion.
Describe the mechanism of image acquisition for a nuclear bone scan.
Radio-isotope: Technetium-99
Radio-pharmaceutical: Methylene diphosphonate
Images are obtained about 4 hours after the injection, as this allows time for the bones to take up the radio-pharmaceutical.
What is the main indication for a nuclear bone scan?
Bone scans are the best modality for screening for bony metastases. It is more sensitive than MRI for bony metastases.
They are also the most sensitive for fractures not seen on radiography.
However, they are not specific, so fractures, degenerative changes, metastases and
osteomyelitis will also produce increased uptake
Describe the features of a normal bone scan.
- Symmetric uptake of radiotracer, e.g. symmetry in shoulders, ribs, long bones
- Usually there is increased uptake in the skull uniformly
- Bladder is bright due to renal clearance of radiotracer
Both anterior and posterior images are taken to more comprehensively visualise the bones.
NB: This patient also has scoliosis.
Describe the features in a bone scan indicating metastases.
- Asymmetric uptake of radiotracer in areas of greatest bone turnover (therefore, note that blastic metastatic lesions are clear, but lytic lesions may be missed) - high yield
- May be multiple regions
The patient shown here has bony metastases from her breast cancer in her ribs, spine and pelvis, for starters.
Describe the features in a normal MPS.
Images are obtained on 3 different planes and imaged both at stress and at rest.
Describe the features in an abnormal MPS.
Note that in the regions where the white arrows are, there are differences in perfusion at stress and at rest.
Stress causes reduced perfusion to the heart, indicating ischaemia.
If the hypoperfused area was dark even at rest, perhaps it could indicate an infarct.
Describe the method of acquisition for a thyroid nuclear scan.
Radio-pharmaceutical [High Yield]
- Radioactive iodine, or
- Technetium-99m pertechnate
What types of nodules can be found in the thyroid on a nuclear medicine scan?
Majority of nodules are benign.
Major categories are:
- Benign vs. cancerous nodules
- ‘Hot’ (increased uptake) vs. ‘cold’ (decreased uptake) nodules
Usually, a solitary ‘cold’ nodule is more likely to indicate cancer than a ‘hot’ nodule.
Describe an abnormal thyroid scan compared to a normal one.
See attached image.
