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ARRT Nuclear Medicine practice questions

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Question 1Diagnostic Procedures / Clinical Applications

Which radiopharmaceutical is used for routine skeletal scintigraphy?

  1. Tc-99m mebrofenin
  2. Tc-99m sulfur colloid
  3. Tc-99m medronate (MDP) Correct answer.
  4. Tc-99m pentetate (DTPA)

Explanation

MDP is a diphosphonate that adsorbs onto the hydroxyapatite crystal surface of bone, with roughly half of the injected dose localizing to the skeleton. The remainder is cleared by the kidneys, which provides the bone-to-soft-tissue contrast needed for imaging.

Question 2Diagnostic Procedures / Clinical Applications

On a hepatobiliary (HIDA) scan, continued nonvisualization of the gallbladder at 4 hours after injection is most consistent with:

  1. Common bile duct obstruction
  2. Diffuse hepatocellular dysfunction
  3. Acute cholecystitis Correct answer.
  4. Chronic acalculous cholecystitis

Explanation

When tracer reaches the bowel but the gallbladder never fills, the cystic duct is obstructed, which is the hallmark of acute cholecystitis. Delayed imaging to 4 hours, sometimes with morphine augmentation, raises specificity for that diagnosis.

Question 3Diagnostic Procedures / Clinical Applications

A mismatched perfusion defect on a V/Q lung scan, with reduced perfusion but preserved ventilation, is the classic scintigraphic sign of:

  1. Atelectasis
  2. Pulmonary embolism Correct answer.
  3. Pneumonia
  4. Chronic obstructive pulmonary disease

Explanation

Airway disease reduces both ventilation and perfusion to the same region, so defects appear matched. An embolus occludes the vessel and abolishes perfusion while ventilation to that segment remains intact, producing the mismatch.

Question 4Diagnostic Procedures / Clinical Applications

Tc-99m pertechnetate is the radiopharmaceutical of choice for detecting a Meckel diverticulum because it:

  1. Accumulates in the diverticulum's fecal contents
  2. Is trapped by the diverticulum's lymphoid tissue
  3. Is taken up by ectopic gastric mucosa Correct answer.
  4. Binds to ectopic pancreatic tissue

Explanation

Pertechnetate is actively trapped by gastric mucosa, so a diverticulum containing ectopic gastric mucosa shows a focal area of increasing activity, usually in the right lower quadrant. Pretreatment with an H2 blocker or glucagon can improve target-to-background ratio.

Question 5Diagnostic Procedures / Clinical Applications

For a thyroid uptake measurement, Tc-99m pertechnetate differs from radioiodine in that pertechnetate is:

  1. Trapped but not organified Correct answer.
  2. Organified but not trapped
  3. Bound to thyroglobulin in colloid
  4. Neither trapped nor organified

Explanation

Pertechnetate is handled by the sodium-iodide symporter but is not a substrate for thyroid peroxidase, so it cannot be incorporated into thyroglobulin. This makes it suitable for imaging and trapping measurements but not for assessing organification or for therapy.

Question 6Diagnostic Procedures / Clinical Applications

Which radiopharmaceutical provides the best assessment of regional renal cortical function and scarring?

  1. Tc-99m pertechnetate
  2. Tc-99m MAG3
  3. Tc-99m DTPA
  4. Tc-99m DMSA Correct answer.

Explanation

DMSA binds to proximal tubular cells and is retained in the cortex, yielding high cortical-to-background images that depict functioning cortex and scars. MAG3 and DTPA are rapidly cleared agents used for dynamic flow and clearance studies.

Question 7Diagnostic Procedures / Clinical Applications

The uptake of 18F-FDG in a tumor reflects:

  1. Cell membrane integrity
  2. Regional blood flow
  3. Glucose metabolism Correct answer.
  4. DNA synthesis

Explanation

FDG is a glucose analog that is phosphorylated by hexokinase but not further metabolized, so it is trapped intracellularly in proportion to glycolytic rate. Malignant cells typically overexpress glucose transporters and hexokinase, giving high uptake.

Question 8Diagnostic Procedures / Clinical Applications

For sentinel lymph node mapping in breast cancer, the radiotracer is typically injected:

  1. Into the tumor bed
  2. Intradermally around the areola Correct answer.
  3. Intravenously
  4. Into the subclavian artery

Explanation

Intradermal or periareolar injection enters the rich dermal lymphatic plexus that drains the breast, allowing the first draining node to be identified quickly with a gamma probe. The node is then localized surgically and checked for radioactivity before excision.

Question 9Diagnostic Procedures / Clinical Applications

A whole-body bone scan shows intensely increased, diffuse skeletal uptake with faint or absent renal and soft-tissue activity. This superscan appearance is most often due to:

  1. Recent treatment with colony-stimulating factors
  2. Widespread skeletal metastases Correct answer.
  3. Hyperparathyroidism
  4. Severe renal failure

Explanation

When the skeleton is diffusely laden with metastatic disease, most of the tracer is extracted before it can be excreted, so the kidneys appear faint. Prostate and breast carcinoma are the classic causes of this pattern.

Question 10Diagnostic Procedures / Clinical Applications

Which patient preparation is required before a dipyridamole myocardial perfusion study?

  1. Avoiding caffeine for 12-24 hours Correct answer.
  2. Fasting for 12 hours
  3. Stopping beta-blockers for 48 hours
  4. Premedication with atropine

Explanation

Caffeine and theophylline are adenosine receptor antagonists that block vasodilator-induced hyperemia and can produce a false-negative study. They must be withheld, whereas beta-blockers and food intake do not blunt a vasodilator stress response.

Question 11Diagnostic Procedures / Clinical Applications

In a captopril renogram performed for suspected renovascular hypertension, a positive study is characterized by:

  1. Rapid washout of tracer from the affected kidney
  2. Deterioration of the renogram curve in the stenotic kidney Correct answer.
  3. Symmetrical time-to-peak in both kidneys
  4. Improved tracer uptake in the affected kidney

Explanation

ACE inhibition lowers angiotensin II-mediated efferent arteriolar tone, so in a kidney with a tight renal artery stenosis the glomerular filtration rate falls and the renogram deteriorates compared with baseline. A normal study shows no change or symmetric curves.

Question 12Diagnostic Procedures / Clinical Applications

On a furosemide renogram, which finding indicates true obstruction rather than a dilated but unobstructed collecting system?

  1. Tracer half-time greater than 20 minutes Correct answer.
  2. An initial uptake phase in the cortex
  3. Prompt response to furosemide
  4. Tracer accumulation in the bladder

Explanation

In a dilated but unobstructed system, furosemide-induced diuresis washes tracer out with a half-time under about 10 to 15 minutes. A prolonged half-time beyond 20 minutes indicates mechanical obstruction, with values in between considered equivocal.

Question 13Diagnostic Procedures / Clinical Applications

Which radiopharmaceutical is preferred for detecting intermittent lower gastrointestinal bleeding because it can be imaged over a prolonged period?

  1. Tc-99m mebrofenin
  2. Tc-99m labeled red blood cells Correct answer.
  3. In-111 pentetreotide
  4. Tc-99m sulfur colloid

Explanation

Labeled red blood cells remain within the vascular space with a long biological half-life, allowing repeated imaging for up to 24 hours so that intermittent bleeding can be captured. Sulfur colloid is cleared by the reticuloendothelial system within minutes and limits the imaging window.

Question 14Diagnostic Procedures / Clinical Applications

On a dual-phase Tc-99m sestamibi parathyroid scan, a parathyroid adenoma typically appears as:

  1. A photopenic defect that fills in on delayed images
  2. Focal retention on delayed images Correct answer.
  3. Early uptake that fades on delayed images
  4. Focal uptake only after perchlorate administration

Explanation

Sestamibi washes out of normal thyroid tissue more rapidly than from parathyroid adenoma, so a persistent focus on the 2-hour delayed images localizes the adenoma. Single-isotope dual-phase imaging takes advantage of this differential washout.

Question 15Diagnostic Procedures / Clinical Applications

In a standard solid-phase gastric emptying study, the result is usually expressed as the:

  1. Ratio of antral to fundal activity
  2. Time for half the meal to empty Correct answer.
  3. Total counts in the small bowel at 30 minutes
  4. Peak counts in the stomach

Explanation

A time-activity curve is generated over the stomach, and the half-emptying time is derived from it, which is prolonged in gastroparesis. The solid meal is labeled with a tracer that is not absorbed, so counts reflect retained food.

Question 16Diagnostic Procedures / Clinical Applications

Which V/Q scan pattern meets the PIOPED criteria for a high-probability study for pulmonary embolism?

  1. At least two large mismatched defects Correct answer.
  2. One moderate mismatched defect with a normal chest radiograph
  3. Matched defects in three or more segments
  4. A single small matched subsegmental defect

Explanation

High probability requires at least two large mismatched perfusion defects, each involving more than 75 percent of a segment, with normal ventilation and no corresponding radiographic opacity. A single moderate mismatch is only intermediate probability.

Question 17Diagnostic Procedures / Clinical Applications

Morphine sulfate is sometimes administered during a HIDA scan to:

  1. Accelerate hepatic clearance of tracer
  2. Promote gallbladder filling Correct answer.
  3. Prevent biliary reflux into stomach
  4. Reduce patient motion during imaging

Explanation

Morphine raises sphincter of Oddi tone and increases intraductal pressure, which forces tracer into the gallbladder when the cystic duct is patent. If the gallbladder still fails to fill after morphine, cystic duct obstruction is confirmed.

Question 18Diagnostic Procedures / Clinical Applications

On a Tc-99m sulfur colloid liver-spleen scan, focal nodular hyperplasia usually appears as:

  1. Diffusely increased splenic uptake
  2. A defect that fills in only with hepatobiliary tracer
  3. Normal or increased uptake from Kupffer cells Correct answer.
  4. A photon-deficient defect

Explanation

Focal nodular hyperplasia contains Kupffer cells, so it takes up sulfur colloid at a level equal to or greater than normal liver. Hepatic adenoma lacks Kupffer cells and therefore appears as a photon-deficient defect.

Question 19Diagnostic Procedures / Clinical Applications

I-123 MIBG scintigraphy is most useful for imaging:

  1. Bone metastases from prostate cancer
  2. Pheochromocytoma and neuroblastoma Correct answer.
  3. Infection and inflammation
  4. Somatostatin receptor-positive tumors

Explanation

MIBG is a norepinephrine analog taken up by the amine transporter of adrenergic tissue, so it localizes chromaffin tumors such as pheochromocytoma, paraganglioma, and neuroblastoma. Normal uptake is seen in the salivary glands, liver, spleen, and heart.

Question 20Diagnostic Procedures / Clinical Applications

During a Tc-99m DTPA study for suspected brain death, the finding of tracer in the facial and nasal areas with no intracranial activity is called the:

  1. Cranial blush
  2. Empty delta sign
  3. Hot nose sign Correct answer.
  4. Tentorial sign

Explanation

When cerebral perfusion has ceased, external carotid flow persists and is seen as prominent activity in the nose and face while the cerebral hemispheres remain photopenic. This hot nose sign supports the diagnosis of brain death in the appropriate clinical setting.

Question 21Diagnostic Procedures / Clinical Applications

A patient with severe left ventricular dysfunction shows a region of reduced perfusion on SPECT but preserved FDG uptake on PET. This pattern indicates:

  1. Viable hibernating myocardium Correct answer.
  2. Normal myocardium
  3. Artifact from diaphragmatic attenuation
  4. Transmural myocardial infarction

Explanation

Perfusion-metabolism mismatch, meaning reduced perfusion with preserved glucose metabolism, identifies hibernating myocardium that may recover function after revascularization. A matched reduction in both perfusion and FDG uptake indicates scar.

Question 22Diagnostic Procedures / Clinical Applications

Compared with In-111 labeled leukocyte imaging, Ga-67 citrate scintigraphy is less specific for infection mainly because gallium:

  1. Accumulates in tumors and sterile inflammation Correct answer.
  2. Cannot be imaged until 24-48 hours after injection
  3. Has a physical half-life too short for delayed imaging
  4. Is excreted primarily through the lungs and gut

Explanation

Gallium binds transferrin and lactoferrin, so it localizes in neoplasms, healing wounds, and sterile inflammatory foci as well as in infection, lowering specificity. Labeled leukocytes migrate specifically toward chemotactic stimuli of infection.

Question 23Diagnostic Procedures / Clinical Applications

On a testicular scan, which pattern favors acute epididymitis over testicular torsion?

  1. Absent perfusion on the dynamic phase
  2. Delayed appearance of both testes
  3. Increased perfusion and uptake Correct answer.
  4. A photopenic defect in the affected hemiscrotum

Explanation

Inflammation increases blood flow and capillary permeability, producing a hot hemiscrotum on both the flow and static phases. Torsion abolishes arterial supply and produces decreased flow with a photopenic testis, requiring immediate surgical attention.

Question 24Diagnostic Procedures / Clinical Applications

Which study is used to detect vesicoureteral reflux without intravenous tracer administration?

  1. Direct radionuclide cystogram Correct answer.
  2. Captopril renogram
  3. Indirect radionuclide cystogram
  4. Diuretic renogram

Explanation

In a direct radionuclide cystogram, tracer is instilled into the bladder through a catheter, so reflux is detected without any intravenous injection. The indirect technique uses intravenously administered MAG3 and relies on voiding after renal excretion.

Question 25Diagnostic Procedures / Clinical Applications

A shunt patency study is performed by injecting Tc-99m DTPA into the reservoir of a ventriculoperitoneal shunt. Normal patency is demonstrated by:

  1. Accumulation of activity over the cerebral convexity
  2. Rapid clearance of activity from the tubing
  3. Activity confined to the shunt tubing
  4. Activity appearing in the peritoneal cavity Correct answer.

Explanation

After reservoir injection, tracer should flow through the distal tubing and reach the peritoneal cavity within minutes, confirming distal patency. Persistence of activity within the tubing or reservoir indicates obstruction.

Question 26Diagnostic Procedures / Clinical Applications

Which radiopharmaceutical is used for a Meckel's diverticulum scan?

  1. Tc-99m sulfur colloid
  2. Tc-99m MDP
  3. In-111 oxine-labeled leukocytes
  4. Tc-99m pertechnetate Correct answer.

Explanation

Tc-99m pertechnetate is taken up by ectopic gastric mucosa, which is present in most symptomatic Meckel's diverticula. Focal uptake in the right lower abdomen that appears with gastric mucosa and moves with bowel is characteristic.

Question 27Diagnostic Procedures / Clinical Applications

Gated equilibrium blood-pool (MUGA) imaging is most commonly performed to measure which parameter?

  1. Glomerular filtration rate
  2. Thyroid radioiodine uptake
  3. Left ventricular ejection fraction Correct answer.
  4. Hepatic extraction fraction

Explanation

Gated blood-pool imaging uses Tc-99m-labeled red blood cells to create ECG-synchronized frames of the cardiac chambers. The change in counts between end diastole and end systole is used to calculate left ventricular ejection fraction and wall motion.

Question 28Diagnostic Procedures / Clinical Applications

A 24-hour radioiodine uptake measurement is used primarily to evaluate which thyroid function?

  1. Bone mineralization rate
  2. Renal tubular secretion of iodide
  3. Parathyroid hormone reserve
  4. Thyroid iodine trapping and organification Correct answer.

Explanation

The 24-hour radioiodine uptake quantifies the fraction of administered I-123 or I-131 retained by the thyroid. It reflects both iodide trapping and organification and is used to evaluate hyperthyroidism and thyroiditis.

Question 29Diagnostic Procedures / Clinical Applications

Which radiopharmaceutical is used for a standard whole-body bone scan?

  1. Tc-99m MDP Correct answer.
  2. Tc-99m sulfur colloid
  3. Tc-99m pertechnetate
  4. Tc-99m DTPA

Explanation

Tc-99m MDP (or an equivalent diphosphonate) adsorbs to hydroxyapatite in bone and is the standard agent for skeletal scintigraphy. Areas of increased bone turnover show increased uptake.

Question 30Diagnostic Procedures / Clinical Applications

On a three-phase Tc-99m MDP bone scan, which pattern favors osteomyelitis over adjacent cellulitis?

  1. Increased arterial flow and blood pool with normal delayed bone uptake
  2. Normal arterial flow and blood pool with increased delayed bone uptake
  3. Decreased arterial flow and blood pool with a photopenic delayed bone defect
  4. Increased arterial flow and blood pool with focally increased delayed bone uptake Correct answer.

Explanation

Osteomyelitis produces hyperemia on the flow and blood-pool phases plus focal osseous uptake on the delayed phase. Cellulitis produces hyperemia without delayed bone localization.

Question 31Diagnostic Procedures / Clinical Applications

A neonate with persistent jaundice undergoes a Tc-99m hepatobiliary scan after phenobarbital pretreatment. Absence of bowel activity at 24 hours is most consistent with which diagnosis?

  1. Common bile duct stone
  2. Acute cholecystitis
  3. Hepatic hemangioma
  4. Biliary atresia Correct answer.

Explanation

In neonatal hepatobiliary scanning, phenobarbital is given to enhance bile flow and enzyme induction. Failure to see tracer in the bowel by 24 hours indicates obstruction to bile excretion and is the classic pattern of biliary atresia.

Question 32Diagnostic Procedures / Clinical Applications

Which preparation is required before a diagnostic I-131 whole-body scan in a patient who has undergone thyroidectomy for thyroid cancer?

  1. A 12-hour fast and bowel preparation
  2. Potassium iodide loading to block the thyroid
  3. A low-iodine diet and TSH stimulation Correct answer.
  4. A high-iodine diet and thyroid hormone suppression

Explanation

Radioiodine uptake by residual thyroid tissue or metastases is maximized by iodine depletion and elevated TSH. A low-iodine diet plus either thyroid hormone withdrawal or recombinant TSH is standard.

Question 33Diagnostic Procedures / Clinical Applications

A hepatic hemangioma is best characterized on which study as a region of increased uptake on delayed images?

  1. Tc-99m labeled RBC SPECT Correct answer.
  2. Tc-99m MDP bone scan
  3. Ga-67 citrate scan
  4. Tc-99m sulfur colloid liver-spleen scan

Explanation

Cavernous hemangiomas have slow blood-pool filling, so labeled RBC imaging shows increased activity on delayed SPECT images. This reflects the lesion's large vascular spaces.

Question 34Diagnostic Procedures / Clinical Applications

I-123 ioflupane (DaTscan) imaging is used to assess which structure or function?

  1. Myocardial sympathetic innervation
  2. Presynaptic dopaminergic terminals in the striatum Correct answer.
  3. Bone marrow reticuloendothelial function
  4. Somatostatin receptor expression

Explanation

Ioflupane binds the dopamine transporter on presynaptic nigrostriatal terminals. Reduced striatal uptake supports a Parkinsonian syndrome rather than essential tremor.

Question 35Diagnostic Procedures / Clinical Applications

Which radiopharmaceutical is used to evaluate splenic sequestration in a child with hereditary spherocytosis?

  1. Heat-damaged Tc-99m labeled RBCs Correct answer.
  2. In-111 oxine-labeled leukocytes
  3. Tc-99m MDP
  4. Tc-99m sulfur colloid

Explanation

Heat-damaged RBCs are trapped preferentially by the spleen, allowing splenic sequestration to be quantified. Comparing splenic with hepatic activity helps determine whether splenectomy is likely to benefit the patient.

Question 36Diagnostic Procedures / Clinical Applications

In-111 pentetreotide (Octreoscan) imaging is most useful for detecting tumors that express which receptor?

  1. Thyroid peroxidase
  2. Somatostatin receptors Correct answer.
  3. Prostate-specific membrane antigen
  4. Dopamine transporters

Explanation

Pentetreotide is a somatostatin analog and binds somatostatin receptors, which are overexpressed by many neuroendocrine tumors. It is used for staging and localization of those tumors.

Question 37Diagnostic Procedures / Clinical Applications

68Ga-PSMA-11 PET/CT is used primarily to evaluate which malignancy?

  1. Neuroendocrine tumors
  2. Differentiated thyroid cancer
  3. Breast carcinoma
  4. Prostate cancer Correct answer.

Explanation

PSMA is overexpressed on prostate cancer cells, so PSMA PET/CT is used for staging and localization of recurrent prostate cancer. It is not a general-purpose oncologic tracer.

Question 38Diagnostic Procedures / Clinical Applications

A renal transplant recipient has rising creatinine. A Tc-99m MAG3 scan shows a progressive tracer collection inferior to the graft that enlarges on delayed images. This finding most likely represents which complication?

  1. Cyclosporine toxicity
  2. Acute tubular necrosis
  3. Acute rejection
  4. Urinary leak Correct answer.

Explanation

A progressive collection of tracer outside the urinary tract that enlarges over time is characteristic of a urine leak or urinoma. It is distinct from parenchymal dysfunction, which alters uptake and excretion rather than creating an expanding extrarenal collection.

Question 39Diagnostic Procedures / Clinical Applications

During a Tc-99m MAA perfusion lung scan, which finding indicates a right-to-left shunt?

  1. Increased tracer uptake in the liver
  2. Multiple segmental perfusion defects in the lungs
  3. Uniform tracer distribution throughout both lungs
  4. Uptake of tracer in the brain and kidneys Correct answer.

Explanation

MAA particles are normally trapped in the pulmonary capillary bed. In a right-to-left shunt, particles bypass the lungs and lodge in systemic capillary beds, producing uptake in organs such as the brain and kidneys.

Question 40Diagnostic Procedures / Clinical Applications

A periprosthetic region shows increased uptake on both In-111 labeled leukocyte imaging and Tc-99m sulfur colloid marrow imaging. This concordant pattern most likely represents which finding?

  1. Acute fracture
  2. Aseptic loosening
  3. Prosthetic joint infection
  4. Normal bone marrow Correct answer.

Explanation

Labeled leukocyte uptake that matches the distribution of bone marrow on sulfur colloid imaging indicates normal marrow rather than infection. Infection is suggested by leukocyte uptake that is discordant with marrow.

Question 41Radiopharmacy and Radiopharmaceuticals

The physical half-life of Tc-99m is:

  1. 6 hours Correct answer.
  2. 110 minutes
  3. 13 hours
  4. 66 hours

Explanation

Tc-99m decays by isomeric transition with a physical half-life of about 6 hours and emits a 140 keV gamma ray. This short half-life limits the useful life of an eluate to roughly 12 hours while keeping patient absorbed dose low.

Question 42Radiopharmacy and Radiopharmaceuticals

A Mo-99/Tc-99m generator is eluted with which solution?

  1. 0.1 N hydrochloric acid
  2. Sodium bicarbonate 8.4%
  3. Sterile water for injection
  4. 0.9% sodium chloride Correct answer.

Explanation

Normal saline passes through the alumina column, and the chloride ion displaces pertechnetate from the column binding sites, yielding sodium pertechnetate. Water alone elutes poorly, and acid or alkaline solutions would degrade the column and the product.

Question 43Radiopharmacy and Radiopharmaceuticals

Which radiopharmaceutical is used for skeletal scintigraphy?

  1. Tc-99m DTPA
  2. Tc-99m MDP Correct answer.
  3. Tc-99m pertechnetate
  4. Tc-99m sulfur colloid

Explanation

Tc-99m MDP adsorbs onto the hydroxyapatite crystal surface of bone, with uptake proportional to regional blood flow and osteoblastic activity. The other agents localize to the reticuloendothelial system, the kidneys, or thyroid and gastric mucosa.

Question 44Radiopharmacy and Radiopharmaceuticals

Which radionuclide has a physical half-life of approximately 110 minutes?

  1. Ga-67
  2. Tc-99m
  3. I-123
  4. F-18 Correct answer.

Explanation

F-18 decays by positron emission with a half-life of about 110 minutes, which limits how far it can be shipped and sets the practical daily workflow for FDG. Tc-99m, Ga-67, and I-123 have much longer half-lives.

Question 45Radiopharmacy and Radiopharmaceuticals

Which radiopharmaceutical is taken up by hepatocytes and excreted into the biliary tree?

  1. Tc-99m sulfur colloid
  2. Tc-99m mebrofenin Correct answer.
  3. Tc-99m RBCs
  4. Tc-99m MAA

Explanation

Iminodiacetic acid derivatives such as mebrofenin are carried into hepatocytes by organic anion transporters and then excreted in bile, allowing assessment of gallbladder filling and biliary patency. The other agents are handled by phagocytes, lung capillaries, or the vascular space.

Question 46Radiopharmacy and Radiopharmaceuticals

Which photon energy is emitted by Tc-99m and makes it well suited to the gamma camera?

  1. 140 keV Correct answer.
  2. 511 keV
  3. 364 keV
  4. 245 keV

Explanation

The 140 keV gamma of Tc-99m is high enough to escape the patient yet low enough to be efficiently collimated and absorbed in a sodium iodide crystal. This favorable energy is a major reason Tc-99m is the most widely used imaging nuclide.

Question 47Radiopharmacy and Radiopharmaceuticals

Which radiopharmaceutical is used for myocardial perfusion imaging?

  1. Tc-99m sestamibi Correct answer.
  2. Tc-99m sulfur colloid
  3. Tc-99m DTPA
  4. Tc-99m MAA

Explanation

Tc-99m sestamibi is a lipophilic cation that accumulates in myocardial mitochondria in proportion to regional blood flow, making it useful for perfusion imaging. The other agents distribute to lung capillaries, the reticuloendothelial system, or the kidneys.

Question 48Radiopharmacy and Radiopharmaceuticals

Which radiopharmaceutical is preferred for thyroid scintigraphy because it delivers a much lower absorbed dose than I-131?

  1. I-131
  2. Tc-99m MAA
  3. I-123 Correct answer.
  4. Ga-67 citrate

Explanation

I-123 decays by electron capture, emitting a 159 keV gamma with no beta particles, so it gives high-quality thyroid images at a fraction of the dose from I-131. I-131 emits beta radiation that deposits a much larger absorbed dose in the gland.

Question 49Radiopharmacy and Radiopharmaceuticals

Which method is used to check a Tc-99m eluate for Mo-99 breakthrough?

  1. Measure the eluate pH with indicator paper
  2. Inspect the eluate for visible particles
  3. Count the eluate in a well counter after 24 hours of decay
  4. Assay through a lead shield in a dose calibrator Correct answer.

Explanation

Mo-99 emits a 740 keV gamma that passes through a lead shield which attenuates the 140 keV photons of Tc-99m. Assaying the shielded vial therefore reveals any Mo-99 present, and the result must not exceed 0.15 kBq Mo-99 per MBq Tc-99m.

Question 50Radiopharmacy and Radiopharmaceuticals

Radiochemical purity of a Tc-99m labeled radiopharmaceutical is determined by which technique?

  1. Dose calibrator assay of the shielded vial
  2. Thin-layer chromatography Correct answer.
  3. Daily constancy testing of the calibrator
  4. Gamma ray spectroscopy of the vial

Explanation

Chromatography on paper or instant thin-layer strips separates the labeled product from free pertechnetate and hydrolyzed-reduced technetium, and the fraction of activity in the product band gives radiochemical purity. Spectroscopy and calibrator assays measure other properties.