Nuclear Medicine for FRCR 2B: How to Identify Classic Scans in the Viva

Nuclear medicine occupies a strange place in FRCR 2B preparation. It is a small fraction of the syllabus, so most candidates postpone it — and then discover in the viva that they have been handed a whole-body scan with no idea what tracer they are even looking at

The reassuring news is that the examiners are not testing you as a nuclear medicine physician. They are testing whether you can identify the study, recognise a classical pattern, and ask for the right correlative imaging. Get those three steps right and the case is largely won.

Here is the framework that makes that possible.

Start With Physiological Distribution, Not Pathology

This is the single most useful principle in nuclear medicine for FRCR 2B candidates: learn what normal looks like first.

Every tracer has a signature pattern of normal uptake. Once you recognise that signature, you know which scan you are looking at. Everything outside that pattern is, by definition, abnormal. Candidates who go straight to hunting for lesions freeze because they cannot orient themselves. Candidates who first say “the lacrimal and salivary glands are lighting up — this is a PSMA PET” have already earned marks and bought themselves thinking time.

Gamma Camera Studies: The Technetium Family

Most gamma studies use technetium-99m bound to a ligand chosen for the target organ.

Tc-99m MDP Bone Scan

MDP binds to hydroxyapatite, so uptake reflects osteoblastic activity. Physiological excretion is renal, so kidneys and bladder always light up. The tracer is highly sensitive but poorly specific — trauma and metastasis both cause focal uptake.

Classical patterns worth memorising:

• Multifocal random uptake across skull, vertebrae, ribs, pelvis and proximal long bones → skeletal metastases, typically prostate, breast or lung.
• Asymmetric, expansile uptake in the pelvis or skull → Paget’s disease. The expansion and asymmetry are the discriminators from metastasis.
• Craniofacial plus unilateral limb involvement in a child → fibrous dysplasia. Note the horizontal linear uptake at epiphyseal growth plates, which tells you the patient is skeletally immature.
• Large expansile lesion with an associated soft tissue mass and photopenic (lytic) centre in a paediatric patient → Ewing’s sarcoma.

Always offer SPECT-CT or correlative CT/MRI to characterise the bone.

Tc-99m DMSA Renal Scan

A cortical agent used to assess renal morphology and detect scarring, typically in recurrent UTI or suspected multicystic dysplastic kidney. Normal kidneys show smooth contours and uniform cortical uptake. Irregular contours with multiple photopenic defects suggest scarring — but remember polycystic kidney disease produces a similar appearance, so clinical history matters.

Tc-99m Pertechnetate Thyroid Scan

Plain pertechnetate is trapped by sodium-iodide symporters, so normal uptake appears in the thyroid, salivary glands and gastric mucosa.

• Increased thyroid uptake with loss of salivary and background activity → hyperfunctioning gland, but only in the context of a suppressed TSH. A raised TSH produces a similar “hungry gland” picture from TSH-induced hyperplasia.
• Absent thyroid uptake with preserved salivary uptake → thyroiditis, again in the context of suppressed TSH. Recent iodine exposure can mimic this.

Stating “in the context of a suppressed TSH” is exactly the qualification examiners want to hear.

I-131 or I-123 MIBG Scan

Physiological uptake occurs in salivary glands, myocardium, liver, bowel, kidneys and bladder. Anything else is abnormal. A right upper quadrant mass in a child suggests neuroblastoma; diffuse skeletal uptake indicates marrow metastases, which are common in neuroblastoma. MIBG is also specific for phaeochromocytoma.

Tc-99m Sestamibi Parathyroid Scan

Sestamibi is taken up by both thyroid and parathyroid adenoma, but washes out of the thyroid faster. Early images at 15–20 minutes and delayed images at around two hours exploit this differential washout — a focus retained on delayed imaging is your adenoma. SPECT-CT localises it, and may reveal an ectopic mediastinal adenoma. Watch for incidental sestamibi-avid lytic bone lesions: these are brown tumours of hyperparathyroidism, and spotting them scores well.

Tc-99m HIDA Scan

Performed in neonates to exclude biliary atresia. Serial imaging up to 24 hours looks for tracer excretion into the bowel. Washout from the myocardium with progressive hepatic accumulation indicates good hepatocyte extraction. Absent bowel activity at 24 hours supports biliary atresia.

Meckel’s Scan and Milk Scan

Pertechnetate is also used to detect heterotopic gastric mucosa in a Meckel’s diverticulum — look for a right iliac fossa focus appearing simultaneously with gastric uptake that does not migrate. The milk scan (Tc-99m sulphur colloid) demonstrates gastro-oesophageal reflux in infants as linear ascent of tracer from stomach into oesophagus.

PET-CT: Four Tracers to Recognise Instantly

PET studies are whole-body and higher resolution than gamma imaging. Identify them by physiological distribution:

Conclusion: Identify, Describe, Correlate

Nuclear medicine is an entire specialty, and trying to master it before FRCR 2B is a poor use of limited revision time. What the exam actually rewards is a narrow, well-drilled skill set: recognise the tracer from its physiological distribution, describe the abnormal uptake in structured language, offer a classical diagnosis, and request correlative anatomical imaging.

Once you have identified the scan, the examiner will usually supply conventional imaging — and from there you are back on familiar radiological ground. As one experienced tutor puts it, half the work is done the moment you name the study correctly.

If you are short on time, focus exclusively on normal distribution patterns and the classical cases above. If you have longer, Fogelman’s atlas of clinical nuclear medicine is an excellent starting point because it presents normal scans before moving to abnormalities.

FRCR Vivacity takeaway: Don’t master nuclear medicine—master the patterns. Recognise the tracer, describe the uptake, suggest the diagnosis, and score the marks.

Watch the Full Session on YouTube

https://youtu.be/eAAM-Bshfc4?si=bqynU_ob7k2ukBDi