Metastatic castration-resistant prostate cancer in a retired teacher is progressing despite enzalutamide and six cycles of docetaxel. PSMA PET-CT shows intense uptake in multiple bone and nodal lesions, and FDG PET shows no lesion without PSMA uptake. Haemoglobin is 11.2 g/dL, platelets 190,000/µL and creatinine 0.9 mg/dL. Which treatment is most appropriate?

Lu-177 PSMA radioligand therapy

Recurrent bright red blood per rectum in a haemodynamically stable man has needed 3 units of blood over a week; colonoscopy and upper GI endoscopy are normal, and the bleeding is intermittent. Which test is most sensitive for slow, intermittent bleeding?

Tc-99m labelled red cell scintigraphy

Catheter mesenteric angiography

Tc-99m sulphur colloid liver scan

Nuclear medicine and PET

24 NEET-PG practice questions on Nuclear medicine and PET, part of Radiology. The first 24 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
Metastatic castration-resistant prostate cancer in a retired teacher is progressing despite enzalutamide and six cycles of docetaxel. PSMA PET-CT shows intense uptake in multiple bone and nodal lesions, and FDG PET shows no lesion without PSMA uptake. Haemoglobin is 11.2 g/dL, platelets 190,000/µL and creatinine 0.9 mg/dL. Which treatment is most appropriate?
1. ALu-177 DOTATATE therapy
2. BLu-177 PSMA radioligand therapy
3. CI-131 MIBG therapy
4. DRadioiodine (I-131) therapy
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Answer: B · Lu-177 PSMA radioligand therapy
Theranostics pairs a diagnostic PSMA PET with a therapeutic beta-emitter aimed at the same target. In PSMA-positive metastatic castration-resistant prostate cancer after an androgen-receptor pathway inhibitor and a taxane, Lu-177 PSMA-617 prolonged survival in the VISION trial. Adequate marrow and kidney function are needed, because these and the salivary glands are the main organs at risk. Key point: PSMA-avid mCRPC after an ARPI and a taxane is treated with Lu-177 PSMA radioligand therapy.
- A: Lu-177 DOTATATE targets somatostatin receptors in neuroendocrine tumours.
- C: MIBG therapy targets neuroblastoma and phaeochromocytoma.
- D: Prostate cancer does not take up iodine.
Question 2 · Medium
Histology of a resected ileal tumour from a man with flushing and diarrhoea shows a well-differentiated neuroendocrine tumour, grade 1, Ki-67 2%. CT shows several liver lesions. Which PET tracer is best to stage the disease and select him for peptide receptor radionuclide therapy?
1. AGa-68 DOTATATE
2. BGa-68 PSMA
3. CF-18 FDG
4. DF-18 sodium fluoride
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Answer: A · Ga-68 DOTATATE
Well-differentiated NETs express somatostatin receptors (mainly type 2) and grow slowly with low glucose use, so Ga-68 DOTATATE PET-CT is far more sensitive than FDG. Strong uptake also shows that the tumour will respond to Lu-177 DOTATATE therapy (theranostics). FDG is more useful in high-grade, poorly differentiated tumours. Key point: A well-differentiated NET is staged with Ga-68 DOTATATE PET-CT, which also selects patients for Lu-177 DOTATATE.
- B: PSMA tracers target prostate cancer.
- C: FDG is often negative in slow-growing grade 1 NETs.
- D: Sodium fluoride images bone turnover only.
Question 3 · Medium
In the surgical ward, a diabetic man has had 20 hours of constant pain below the right costal margin with a temperature of 38.6 °C; sonography is inconclusive because of bowel gas. On cholescintigraphy with Tc-99m mebrofenin, the liver takes up tracer promptly and the common duct and small intestine fill by 30 minutes, yet no gallbladder activity appears by 60 minutes, nor 30 minutes after IV morphine. Which condition is shown?
1. ACommon bile duct obstruction
2. BAcute cholecystitis
3. CHepatocellular dysfunction
4. DNormal gallbladder function
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Answer: B · Acute cholecystitis
In acute calculous cholecystitis a stone impacts in the cystic duct, so tracer reaches the bile duct and bowel but never fills the gallbladder. Morphine contracts the sphincter of Oddi and raises duct pressure, and if the gallbladder still does not fill 30 minutes later, cystic duct obstruction is confirmed. Cholescintigraphy is the most accurate test when ultrasound is equivocal. Key point: On a HIDA scan, bowel seen but gallbladder not seen, even after morphine, means acute cholecystitis.
- A: CBD obstruction stops tracer reaching the duodenum, which is seen here.
- C: Liver uptake is prompt, so hepatocyte function is normal.
- D: A normal gallbladder fills within an hour.
Question 4 · Medium
Recurrent bright red blood per rectum in a haemodynamically stable man has needed 3 units of blood over a week; colonoscopy and upper GI endoscopy are normal, and the bleeding is intermittent. Which test is most sensitive for slow, intermittent bleeding?
1. ACatheter mesenteric angiography
2. BTc-99m sulphur colloid liver scan
3. CDouble-contrast barium enema
4. DTc-99m labelled red cell scintigraphy
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Answer: D · Tc-99m labelled red cell scintigraphy
Labelled red cells stay in the blood pool for hours, so delayed images can catch intermittent bleeding at rates as low as about 0.1 mL/min, much slower than the 0.5-1 mL/min needed for catheter angiography. A positive scan localises the bleeding segment and guides embolisation or surgery, and CT angiography is an alternative when bleeding is active. Key point: Red cell scintigraphy detects slow, intermittent GI bleeding (about 0.1 mL/min), better than angiography.
- A: Angiography needs active bleeding of about 0.5-1 mL/min at the time of injection.
- B: Sulphur colloid is cleared quickly by the liver and spleen and misses intermittent bleeding.
- C: Barium enema does not show bleeding and interferes with later tests.
Question 5 · Medium
After her third febrile urinary tract infection, a girl of 3 has a micturating cystourethrogram showing grade III vesicoureteric reflux on the left. The paediatric nephrologist wants to know whether the left kidney has cortical scars, 6 months after the last infection. Which scan is best?
1. ATc-99m DTPA renogram
2. BTc-99m DMSA scan
3. CTc-99m pertechnetate scan
4. DTc-99m MAG3 renogram
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Answer: B · Tc-99m DMSA scan
DMSA binds to the proximal tubular cells of the renal cortex and stays there, giving static cortical images in which scars appear as photopenic defects with loss of contour. It is the gold standard for cortical scarring and is done 4-6 months after infection, so that acute changes do not mimic scars. DTPA and MAG3 are dynamic agents for function and drainage. Key point: A DMSA static scan 4-6 months after UTI is the gold standard for renal cortical scarring.
- A: DTPA is filtered and used for GFR and drainage, not scars.
- C: Pertechnetate is used for the thyroid and Meckel diverticulum.
- D: MAG3 is used for dynamic renography and drainage.
Question 6 · Hard
An infant of 4 months had left hydronephrosis on antenatal scans. Postnatal ultrasound shows an anteroposterior pelvic diameter of 28 mm with calyceal dilatation and a normal ureter and bladder, and the right kidney is normal. MCU shows no reflux. He is thriving but has had one febrile urinary infection. A Tc-99m MAG3 diuretic renogram shows tracer collecting in the left pelvis with little fall after IV furosemide (drainage half-time over 20 minutes) and a split function of 36% on the left. Serum creatinine is normal. Which management is most appropriate?
1. ALeft pyeloplasty
2. BLeft nephrectomy
3. CAntibiotic prophylaxis alone
4. DRepeat renogram after 1 year only
Answer and explanation in LearnFree account
Question 7 · Medium
About radionuclides used for the thyroid: 1. Tc-99m pertechnetate is trapped by the gland but not organified. 2. I-123 is trapped but not organified. 3. I-131 has a half-life of about 8 days, and its beta emission is used in therapy. 4. A hot nodule with suppression of the rest of the gland is rarely malignant. Which statements are correct?
1. A2 and 4 only
2. B1, 2, 3 and 4
3. C1, 2 and 3 only
4. D1, 3 and 4 only
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Question 8 · Easy
Why is technetium-99m the most used radionuclide for gamma-camera imaging?
1. AIt emits positrons for coincidence imaging
2. B8-day half-life with beta emission
3. C6-hour half-life and a 140 keV gamma ray
4. DIt is made only in a cyclotron
Answer and explanation in LearnFree account
Question 9 · Medium
On FDG PET-CT: 1. The brain normally shows intense FDG uptake. 2. Tuberculosis can show intense uptake that mimics cancer. 3. Brown fat in the neck and supraclavicular regions can take up FDG, more in cold weather. 4. Patients should eat a high-carbohydrate meal an hour before injection. Which statements are correct?
1. A1, 2, 3 and 4
2. B2, 3 and 4 only
3. C1 and 2 only
4. D1, 2 and 3 only
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Question 10 · Hard
Four months after delivery, a mother who is still breastfeeding has had a total thyroidectomy for a 3 cm papillary thyroid carcinoma with central nodal metastases. The tumour board advises radioiodine (I-131) remnant ablation, and she asks what she must do about breastfeeding. What is the correct advice?
1. AStop breastfeeding completely before I-131
2. BExpress and discard milk for 2 days
3. CPause breastfeeding for 24 hours only
4. DContinue, as I-131 does not enter milk
Answer and explanation in LearnFree account
Question 11 · Hard
A primigravida at 30 weeks has had sudden breathlessness and pleuritic chest pain since morning. Pulse is 112/min, SpO2 93% on air and BP 118/76 mmHg. ECG shows sinus tachycardia, and the chest X-ray (with abdominal shielding) is normal. Compression ultrasound of both legs shows no DVT. She has no asthma or lung disease, serum creatinine is 0.6 mg/dL, D-dimer is raised, and both CT pulmonary angiography and lung scintigraphy are available. Her temperature is normal. Low molecular weight heparin has been started. Which test is preferred to confirm or exclude pulmonary embolism?
1. AMRI chest without contrast
2. BD-dimer to exclude embolism
3. CCatheter pulmonary angiography
4. DPerfusion (V/Q) lung scintigraphy
Answer and explanation in LearnFree account
Question 12 · Medium
Three-phase bone scan of a child with fever for 4 days and pain over the upper tibia, with normal X-rays: increased flow in the first phase, increased blood pool in the second and intense focal uptake in the metaphysis on 3-hour delayed images. What is the diagnosis?
1. ACellulitis of the overlying soft tissue
2. BBone infarct
3. CAcute osteomyelitis
4. DOld healed fracture
Answer and explanation in LearnFree account
Question 13 · Easy
A toddler passes a large amount of maroon blood per rectum without pain, and haemoglobin falls from 11.2 to 7.9 g/dL. Upper GI endoscopy is normal, and a Tc-99m pertechnetate scan is ordered. Which tissue does this scan detect?
1. AAny actively bleeding vessel
2. BEctopic pancreatic tissue
3. CInflamed ileal mucosa
4. DEctopic gastric mucosa
Answer and explanation in LearnFree account
Question 14 · Medium
A diabetic woman arrives for a staging FDG PET-CT for lymphoma after a breakfast of idli and tea, and her capillary glucose is 320 mg/dL. The nuclear medicine technologist calls the physician. What should be done?
1. ADouble the FDG dose
2. BGive IV insulin and inject FDG at once
3. CPostpone the scan until glucose is controlled
4. DProceed, as glucose does not affect FDG
Answer and explanation in LearnFree account
Question 15 · Easy
Bone scan of a man with prostate cancer and a PSA of 210 ng/mL shows intense, uniform uptake throughout the axial skeleton and long bones, with very faint kidneys and almost no bladder activity. What is this pattern called?
1. ARenal failure with poor excretion
2. BSuperscan from diffuse metastases
3. CFlare phenomenon after therapy
4. DNormal bone scan
Answer and explanation in LearnFree account
Question 16 · Easy
PET-CT with F-18 fluorodeoxyglucose (FDG) is done to stage a lung cancer. Why does FDG collect in the tumour cells?
1. AIt is taken up by osteoblasts
2. BIt binds to somatostatin receptors on cells
3. CPhosphorylated FDG is trapped in the cell
4. DIt is built into tumour DNA
Answer and explanation in LearnFree account
Question 17 · Medium
For sentinel lymph node biopsy in early breast cancer, which radiotracer is injected near the tumour or areola?
1. ATc-99m methylene diphosphonate
2. BTc-99m labelled colloid
3. CTc-99m DMSA
4. DF-18 FDG
Answer and explanation in LearnFree account
Question 18 · Medium
Two years after radical prostatectomy for a Gleason 4+3 cancer, a retired engineer has a PSA that has risen from undetectable to 0.4 ng/mL. CT of the abdomen and pelvis and a Tc-99m MDP bone scan are normal. Which imaging is most likely to find the site of recurrence?
1. ARepeat bone scan in 3 months
2. BPSMA PET-CT
3. CMRI of the brain
4. DFDG PET-CT
Answer and explanation in LearnFree account
Question 19 · Medium
Ten days after a sore throat, a nurse has a painful, tender thyroid with pain radiating to the jaw, palpitations and a temperature of 38 °C. ESR is 86 mm/h, free T4 is raised and TSH is suppressed. Radioactive iodine uptake at 24 hours is 2% (normal about 10-30%). What is the most appropriate treatment?
1. ARadioiodine ablation
2. BCarbimazole
3. CTotal thyroidectomy
4. DNSAID and a beta-blocker
Answer and explanation in LearnFree account
Question 20 · Medium
Interim FDG PET-CT after two cycles of ABVD in a student with stage II Hodgkin lymphoma: the residual mediastinal mass now shows uptake above the mediastinal blood pool but less than or equal to the liver (Deauville score 3). No new lesions are seen. How is this response classed?
1. APartial metabolic response
2. BProgressive metabolic disease
3. CComplete metabolic response
4. DNo metabolic response
Answer and explanation in LearnFree account
Question 21 · Medium
Skeletal survey of a man with back pain, serum calcium 11.6 mg/dL, creatinine 1.9 mg/dL and an M band on electrophoresis shows multiple punched-out lytic lesions in the skull and pelvis. A Tc-99m MDP bone scan done earlier at another centre was reported as normal. What explains the normal bone scan?
1. AMyeloma lesions lack osteoblastic activity
2. BMDP binds only to bone marrow
3. CThe lesions are too small to resolve
4. DRenal impairment blocks bone uptake
Answer and explanation in LearnFree account
Question 22 · Hard
At the paediatric surgery clinic, a baby of 7 weeks has had jaundice since the second week, with clay-coloured stools and dark urine, and weight gain has been poor. Conjugated bilirubin is 6.8 mg/dL of a total of 9.2 mg/dL, GGT is 480 U/L and alpha-1 antitrypsin level is normal. Ultrasound shows a small gallbladder that does not contract and a triangular echogenic cord at the porta. After 5 days of phenobarbitone, a hepatobiliary scan shows good liver uptake but no tracer in the bowel even at 24 hours. What is the next step?
1. AOperative cholangiogram and Kasai portoenterostomy
2. BUrsodeoxycholic acid alone
3. CContinue phenobarbitone and review at 3 months
4. DImmediate liver transplantation
Answer and explanation in LearnFree account
Question 23 · Medium
Serum calcium 11.8 mg/dL and PTH 210 pg/mL with renal stones in a homemaker from Thrissur. Dual-phase Tc-99m sestamibi imaging shows a focus below the lower pole of the left thyroid lobe that stays bright on 2-hour delayed images while thyroid activity washes out, and neck ultrasound shows a 1.6 cm hypoechoic nodule there. What is the next step?
1. AFocused left inferior parathyroidectomy
2. BTotal thyroidectomy
3. CRadioiodine therapy
4. DFour-gland exploration with total parathyroidectomy
Answer and explanation in LearnFree account
Question 24 · Easy
Tc-99m pertechnetate thyroid scan of a woman with weight loss, tremor, proptosis, TSH under 0.01 mIU/L and a high free T4 shows a symmetrically enlarged gland with diffusely increased uptake and very low background activity. What is the diagnosis?
1. AGraves disease
2. BToxic adenoma
3. CSubacute thyroiditis
4. DToxic multinodular goitre
Answer and explanation in LearnFree account

Nuclear medicine and PET

Histology of a resected ileal tumour from a man with flushing and diarrhoea shows a well-differentiated neuroendocrine tumour, grade 1, Ki-67 2%. CT shows several liver lesions. Which PET tracer is best to stage the disease and select him for peptide receptor radionuclide therapy?

Recurrent bright red blood per rectum in a haemodynamically stable man has needed 3 units of blood over a week; colonoscopy and upper GI endoscopy are normal, and the bleeding is intermittent. Which test is most sensitive for slow, intermittent bleeding?

After her third febrile urinary tract infection, a girl of 3 has a micturating cystourethrogram showing grade III vesicoureteric reflux on the left. The paediatric nephrologist wants to know whether the left kidney has cortical scars, 6 months after the last infection. Which scan is best?

Why is technetium-99m the most used radionuclide for gamma-camera imaging?

Three-phase bone scan of a child with fever for 4 days and pain over the upper tibia, with normal X-rays: increased flow in the first phase, increased blood pool in the second and intense focal uptake in the metaphysis on 3-hour delayed images. What is the diagnosis?

A toddler passes a large amount of maroon blood per rectum without pain, and haemoglobin falls from 11.2 to 7.9 g/dL. Upper GI endoscopy is normal, and a Tc-99m pertechnetate scan is ordered. Which tissue does this scan detect?

A diabetic woman arrives for a staging FDG PET-CT for lymphoma after a breakfast of idli and tea, and her capillary glucose is 320 mg/dL. The nuclear medicine technologist calls the physician. What should be done?

Bone scan of a man with prostate cancer and a PSA of 210 ng/mL shows intense, uniform uptake throughout the axial skeleton and long bones, with very faint kidneys and almost no bladder activity. What is this pattern called?

PET-CT with F-18 fluorodeoxyglucose (FDG) is done to stage a lung cancer. Why does FDG collect in the tumour cells?

For sentinel lymph node biopsy in early breast cancer, which radiotracer is injected near the tumour or areola?

Two years after radical prostatectomy for a Gleason 4+3 cancer, a retired engineer has a PSA that has risen from undetectable to 0.4 ng/mL. CT of the abdomen and pelvis and a Tc-99m MDP bone scan are normal. Which imaging is most likely to find the site of recurrence?

Interim FDG PET-CT after two cycles of ABVD in a student with stage II Hodgkin lymphoma: the residual mediastinal mass now shows uptake above the mediastinal blood pool but less than or equal to the liver (Deauville score 3). No new lesions are seen. How is this response classed?

Tc-99m pertechnetate thyroid scan of a woman with weight loss, tremor, proptosis, TSH under 0.01 mIU/L and a high free T4 shows a symmetrically enlarged gland with diffusely increased uptake and very low background activity. What is the diagnosis?