RadCases Plus Q&A Nuclear Medicine (eBook)

Case Questions and Answers

The questions and answers in the following section are numbered as cases 1 through 100. The questions correspond to the respectively numbered case reviews and are intended to be answered after working through the cases.

■ Case 1

1.The most reliable sign of a “metastatic superscan” on bone scintigraphy is:

a)Decreased soft tissue and renal activity

b)An abrupt decrease of osseous activity beyond the proximal extremities

c)Diffusely increased activity of the entire (axial and appendicular) skeleton

d)No focal osseous lesion

The correct answer is (b). Abrupt decrease of osseous activity beyond the proximal extremities is due to the fact that typical skeletal metastases localize to the hematopoietic (red) marrow, which is located centrally in adults.

2.Which of the following would be least likely to cause diffusely increased uptake in the entire axial and appendicular skeleton?

a)A 60-year-old man with prostate cancer

b)A 2-year-old girl with metastatic neuroblastoma

c)A 50-year-old woman with hyperparathyroidism

d)A 40-year-old man with chronic kidney disease

The correct answer is (a). Increased uptake throughout the entire axial and appendicular skeleton describes a “metabolic superscan,” which can be seen in patients with metabolic bone disease such as hyperparathyroidism or in pediatric patients in which red marrow remains diffuse. A 60-year-old man with prostate cancer would display a “metastatic superscan” in which there would be decreased osseous activity beyond the proximal appendicular skeleton.

■ Case 2

1.All of the following are treatment options for Graves’ disease except:

a)Methimazole

b)Surgical resection

c)Iodinated contrast

d)Radioiodine ablation

The correct answer is (c). Iodinated contrast can inhibit radioiodine uptake and thereby interfere with a thyroid uptake and scan and at one time was used to treat hyperthyroidism due to Wolff–Chaikoff effect, which can transiently suppress organification of iodine. However, it is not considered a modern treatment option, unlike the other choices.

2.True or false: Diffusely (no nodules) elevated thyroid radioiodine uptake on thyroid uptake and scan is pathognomonic for Graves’ disease.

a)True

b)False

The correct answer is (b). Although it is most commonly Graves disease, there are other possibilities. Diffuse, elevated thyroid radioiodine uptake can also be seen in some hypothyroid patients and in iodine-deficient patients with increased dose of iodine from iodinate contrast (e.g., Jod–Basedow phenomenon). And although rare, pituitary tumors can secrete increased amounts of TSH, causing diffusely increased uptake and hyperthyroidism.

■ Case 3

1.What is the maximum allowed effective dose equivalent to an individual member of the general public?

a)5.0 rem

b)0.1 rem

c)0.5 rem

d)50 rem

The correct answer is (b). Annual radiation dose limit for members of the public may not exceed 0.1 rem/year (1 mSv/year) total effective dose equivalent (TEDE).

2.What is the annual exposure dose limit to a radiation worker?

a)5.0 rem

b)0.1 rem

c)0.5 rem

d)50 rem

The correct answer is (a). Annual occupational dose limit for an adult radiation worker is 5.0 rem (50 mSv) total effective dose equivalent (TEDE).

3.What is the exposure dose limit to the extremity of a radiation worker?

a)5.0 rem

b)0.1 rem

c)0.5 rem

d)50 rem

The correct answer is (d). Organ-specific annual exposure limits are:

•50 rem (500 mSv) to the extremities. Shallow dose equivalent.

•50 rem (500 mSv) to any organ except the lens of the eye. Deep dose equivalent (DDE) 1 committed dose equivalent (CDE).

•15 rem (150 mSv) to the lens of the eye. Lens dose equivalent.

■ Case 4

1.Which of the following dementias would be most likely to involve the lateral occipital cortices with preservation of the posterior cingulate gyri on FDG-PET?

a)Alzheimer’s dementia

b)Multi-infarct dementia

c)Lewy body dementia

d)Frontotemporal dementia

The correct answer is (c). Preservation of the posterior cingulate gyrus can be present in Lewy body dementia (cingulate island sign), whereas it is commonly involved in Alzheimer’s dementia. Alzheimer’s dementia and frontotemporal dementia spare the occipital cortex, whereas Lewy body dementia involves the occipital cortex.

2.Which of the following conditions can mimic multiinfarct dementia findings on FDG-PET?

a)Alzheimer’s dementia

b)AIDS-associated dementia

c)Lewy body dementia

d)Tc99m MIBI The correct answer is (b). Note that with an increased prevalence of PET scanners, FDG is better than Tl-201 in identifying hibernating myocardium, if done with proper protocol (i.e., administering glucose and insulin).

■ Case 5

1.On gated rest-stress myocardial perfusion scintigraphy, hibernating myocardium may have the appearance of:

a)Reversible ischemia

b)Stunned myocardium

c)Infarcted myocardium

d)Attenuation artifact

The correct answer is (c). Without the benefit of additional imaging, such as F-18 FDG images or delayed Tl-201 images, infarcted and hibernating myocardium both have perfusion abnormalities on both stress and rest imaging with associated hypokinesis. Additional imaging will reveal metabolic activity or delayed reversibility confirming hibernating myocardium. Stunned myocardium, usually found immediately after angioplasty in a patient with ongoing MI, typically has normal or near-normal perfusion with hypokinesis, which later demonstrates improved motion if the angioplasty was performed early enough.

2.Viable hibernating myocardium is best detected with which of the following tracers?

a)Tc99m tetrofosmin

b)Rubidium-82

c)Thallium-201

d)Attenuation artifact Tc99m MIBI

The correct answer is (c). Thallium-201 is a potassium channel analogue and redistributes to intact cell membranes (hibernating cells), distinguishing this from infarcted tissue (scar). Perfusion PET with rubidium-82 will show resting defects for both infarcted and hibernating tissue, as 82Rb is a flow agent. Tc99m MIBI and tetrofosmin are mitochondrial binding agents and do not redistribute. With increased prevalence of PET scanners, F-18 FDG is the best modality to identify hibernating myocardium because it will reveal discordant findings when compared with flow agents, if done with proper protocol (i.e., using glucose and insulin).

■ Case 6

1.Which of the following conditions and findings pairs on FDG-PET are correct?

a)Nonfasting altered biodistribution; diffusely increased muscle uptake

b)Brown fat hypermetabolism; diffusely increased muscle uptake

c)Brown fat hypermetabolism; focal skeletal muscle uptake

d)Nonfasting altered biodistribution; focal skeletal muscle uptake

The correct answer is (a). A nonfasting state leads to elevated insulin levels, which drives both glucose and FDG into normal cells, especially muscle, decreasing the available FDG for the tumor cells. This also makes tumor cells less apparent given the lower ratio of tumor to normal tissue.

2.Where is brown fat hypermetabolism least likely to be encountered?

a)Neck

b)Chest

c)Abdomen

d)Pelvis

The correct answer is (d). BAT hypermetabolism is most frequently observed symmetrically in the neck, supraclavicular spaces, paraspinal (thoracic) locations, and often mediastinal locations. Occasionally, BAT uptake is observed below the diaphragm within the upper abdomen (typically perirenal). BAT activity more inferiorly within the pelvis is rare.

3.Which of the following scenarios would result in increased regional skeletal muscle uptake?

a)Hyperinsulinemia (e.g., nonfasting state)

b)Recent exercise

c)Brown fat hypermetabolism

d)Hyperglycemia

The correct answer is (b). Regional skeletal muscle uptake is most commonly seen after recent exercise (a form of myositis). Hyperinsulinemia and hyperglycemia can lead to diffuse skeletal muscle uptake. Brown fat hypermetabolism would be observed symmetrically in the fat located in the neck, supraclavicular spaces, paraspinal (thoracic) locations, and often mediastinal locations, which are readily localized on a PET/CT scan.

■ Case 7

1.On a HIDA scan, which of the following may...