elective 100

What does bone scintigraphy primarily assess?

Osteoblastic activity and bone remodeling.

Which tracer is commonly used for bone scintigraphy?

99mTc-MDP (methylene diphosphonate).

What is the physical half-life of 99mTc?

Approximately 6 hours.

How is 99mTc-MDP predominantly eliminated?

Renal excretion.

Is fasting required before a routine bone scan?

No.

How long after 99mTc-MDP injection are delayed bone images usually acquired?

2–4 hours.

Why encourage hydration and urination after a bone scan?

Improve tracer clearance and reduce bladder radiation exposure.

What does phase 1 of a three-phase bone scan assess?

Regional perfusion immediately after injection.

What does phase 2 of a three-phase bone scan assess?

Blood pool and soft-tissue vascularity.

What does phase 3 of a three-phase bone scan assess?

Delayed osteoblastic activity.

What is the key limitation of bone scintigraphy?

High sensitivity but low specificity.

Why can purely osteolytic metastases be missed on a bone scan?

They may produce little osteoblastic reaction.

Which type of metastasis usually shows marked uptake on bone scintigraphy?

Osteoblastic metastasis.

Does increased bone scan uptake prove malignancy?

No; fracture, arthritis, or infection may also increase uptake.

What are five oncologic uses of nuclear medicine?

Diagnosis, staging, response assessment, follow-up, recurrence detection.

What is 18F-FDG?

A radiolabeled glucose analog used for PET.

Why is FDG uptake not specific for cancer?

Infection and inflammation can also increase glucose uptake.

Which PET tracer targets somatostatin receptors in neuroendocrine tumors?

68Ga-DOTATATE.

Which PET tracer targets PSMA-expressing prostate cancer?

68Ga-PSMA.

Which radiopharmaceutical is used for selected catecholamine-producing tumors?

131I-MIBG.

Which radionuclide is used for differentiated thyroid cancer imaging and therapy?

131I.

Which imaging method uses gallium-67?

Gamma camera/SPECT.

Which imaging method uses gallium-68?

PET.

What is the physical half-life of fluorine-18?

Approximately 110 minutes.

What is the physical half-life of gallium-68?

Approximately 68 minutes.

What is the physical half-life of iodine-131?

Approximately 8 days.

How long should patients generally fast for oncologic FDG PET?

At least 4–6 hours, according to protocol.

Why is fasting required before oncologic FDG PET?

To limit insulin-stimulated skeletal muscle FDG uptake.

Which enzyme phosphorylates intracellular FDG?

Hexokinase.

Why does FDG accumulate inside many cancer cells?

FDG-6-phosphate becomes relatively trapped intracellularly.

Which glucose transporter is often increased in tumors?

GLUT1.

What is the Warburg effect?

Increased glycolytic glucose use in many cancer cells.

Why can iodine-131 be both diagnostic and therapeutic?

Gamma emissions permit imaging; beta emissions deliver therapy.

Why give potassium iodide before certain radioiodinated tracer studies?

Block unwanted thyroid uptake of free radioiodine.

What tracer is commonly used for thyroid scintigraphy?

99mTc-pertechnetate.

Does 99mTc-pertechnetate undergo thyroid hormone organification?

No; it is trapped but not organified.

What transporter mediates thyroid pertechnetate uptake?

Sodium–iodide symporter (NIS).

How soon are thyroid images commonly obtained after pertechnetate injection?

Approximately 15–20 minutes.

What does radioactive iodine uptake (RAIU) quantify?

Percentage of administered iodine accumulated in thyroid tissue.

How does RAIU differ from thyroid scintigraphy?

RAIU quantifies uptake; scintigraphy maps functioning tissue.

What RAIU pattern is typical of Graves disease?

Diffusely increased uptake.

What RAIU pattern is typical of toxic adenoma?

Focal increased uptake with suppression of surrounding tissue.

What scan pattern suggests toxic multinodular goiter?

Patchy or heterogeneous increased uptake.

What RAIU pattern is typical of destructive thyroiditis?

Low uptake during thyrotoxicosis.

Why is RAIU low in destructive thyroiditis despite high T3/T4?

Stored hormones are released without increased synthesis.

What is a hot thyroid nodule?

A hyperfunctioning nodule with increased tracer uptake.

What is a cold thyroid nodule?

A hypofunctioning nodule with decreased or absent uptake.

What evaluation follows discovery of a cold thyroid nodule?

Ultrasound risk assessment; FNA when indicated.

What is the malignancy risk of a truly hyperfunctioning thyroid nodule?

Very low.

Which thyroid cancers commonly retain radioiodine avidity?

Differentiated papillary and follicular carcinomas.

Does postoperative thyroid-bed iodine uptake always indicate cancer?

No; benign thyroid remnant tissue may cause uptake.

Which thyroid cancer is associated with calcitonin and is not treated by conventional radioiodine?

Medullary thyroid carcinoma.

What does SPECT/CT add to iodine scintigraphy?

Anatomical localization of functional uptake.

What tracer is commonly used for parathyroid scintigraphy?

99mTc-sestamibi (MIBI).

What delayed finding suggests a parathyroid adenoma?

Persistent focal sestamibi uptake after thyroid washout.

What is the primary role of parathyroid sestamibi scanning?

Localization after biochemical diagnosis of hyperparathyroidism.

Does a negative sestamibi scan exclude parathyroid disease?

No.

Which tracers are common for myocardial perfusion SPECT?

99mTc-sestamibi and 99mTc-tetrofosmin.

What does myocardial perfusion SPECT assess?

Regional myocardial blood flow and ischemia.

What is the key comparison in myocardial perfusion imaging?

Stress versus rest tracer uptake.

What does a stress-only perfusion defect suggest?

Reversible myocardial ischemia.

What does reduced uptake during both stress and rest suggest?

Fixed defect: scar, hibernation, or attenuation artifact.

Does a fixed perfusion defect prove nonviable myocardium?

No; viability testing may be needed.

Which stress drugs are commonly used for myocardial perfusion imaging?

Adenosine, dipyridamole, or regadenoson.

Why does coronary stenosis produce a stress perfusion defect?

Impaired coronary flow reserve during stress.

Which artery typically supplies the anterior myocardial wall?

Left anterior descending artery (LAD).

Which artery typically supplies the interventricular septum?

LAD.

Which artery typically supplies the lateral myocardial wall?

Left circumflex artery (LCx).

Which artery typically supplies the inferior myocardial wall?

Usually RCA; depends on coronary dominance.

What does ECG-gated SPECT add to perfusion imaging?

LVEF, ventricular volumes, wall motion, and thickening.

What does MUGA stand for?

Multigated Acquisition scan.

What tracer is commonly used for MUGA scanning?

99mTc-labeled red blood cells.

What is MUGA primarily used to measure?

Ventricular function, particularly LVEF.

How does MUGA differ from gated perfusion SPECT?

MUGA measures blood-pool ventricular function, not primarily ischemia.

Which PET tracer is used to assess myocardial viability?

18F-FDG.

How is FDG PET preparation different for myocardial viability?

Glucose loading and sometimes insulin to enhance myocardial uptake.

What is a perfusion–metabolism mismatch?

Low perfusion with preserved FDG uptake: viable hibernating myocardium.

What is a perfusion–metabolism match in a defect?

Low perfusion and low FDG uptake: likely scar.

Can viable hibernating myocardium recover after revascularization?

Yes, potentially.

What does nuclear medicine primarily image compared with conventional radiology?

Function/metabolism rather than primarily anatomy.

Where does detected radiation originate in nuclear medicine?

An administered radiopharmaceutical inside the patient.

What is planar scintigraphy?

Two-dimensional radiopharmaceutical imaging.

What is SPECT?

Three-dimensional gamma-camera emission tomography.

What is PET?

Three-dimensional positron-emission tomography.

What is dynamic scintigraphy?

Sequential tracer images over time, often yielding time–activity curves.

What is the main advantage of hybrid PET/CT or SPECT/CT?

Combines functional findings with anatomical localization.

What characterizes deterministic radiation effects?

Threshold dose; severity rises above threshold.

What characterizes stochastic radiation effects?

Probability rises with dose; severity is not dose-dependent.

What does ALARA stand for?

As Low As Reasonably Achievable.

What are the three core practical radiation safety measures?

Time, distance, and shielding.

What happens to point-source radiation intensity when distance doubles?

It falls to approximately one-quarter.

Does a personal dosimeter protect against radiation?

No; it monitors accumulated exposure.

Is pregnancy an absolute contraindication to every nuclear medicine scan?

No; examinations require careful justification.

What tracer is used for pulmonary perfusion scintigraphy?

Intravenous 99mTc-MAA (macroaggregated albumin).

What is assessed by the ventilation component of a V/Q scan?

Distribution of inhaled radioactive gas or aerosol.

What V/Q pattern classically suggests pulmonary embolism?

Preserved ventilation with decreased perfusion (mismatch).

What does a matched V/Q defect commonly suggest?

Parenchymal lung disease, such as pneumonia or COPD.

Which tracer is used for static renal cortical scintigraphy?

99mTc-DMSA.

What is the major indication for DMSA scintigraphy?

Renal cortical scarring assessment.

What does a renal cortical scar look like on DMSA?

Persistent focal decreased uptake, often with cortical thinning.