A 36-year-old male is taken to the emergency room after jumping from a building. Bilateral fractures to the femur were stabilized at the scene by emergency medical technicians. The patient is lucid upon questioning and his vitals are stable. Pain only at his hips was elicited. Cervical exam was not performed. What is the best imaging study for this patient?

Computed tomography (CT) scan of cervical spine, hips, and lumbar area

AP and lateral radiographs of hips

Lateral radiograph (x-ray) of hips

Magnetic resonance imaging (MRI) of hips, knees, lumbar, and cervical area

Anterior-posterior (AP) and lateral radiographs of hips, knees, lumbar, and cervical area

A 65-year-old man with a 40-pack-year smoking history presents with hemoptysis and a persistent cough. Chest CT shows a 3.5 cm centrally located mass in the right main bronchus. Positron emission tomography confirms a malignant nodule. Bronchoscopy with transbronchial biopsy is performed and a specimen sample of the nodule is sent for frozen section analysis. The tissue sample is most likely to show which of the following tumor types?

Metastasis of colorectal cancer

A 29-year-old woman presents to a medical office complaining of fatigue, nausea, and vomiting for 1 week. Recently, the smell of certain foods makes her nauseous. Her symptoms are more pronounced in the mornings. The emesis is clear-to-yellow without blood. She has had no recent travel out of the country. The medical history is significant for peptic ulcer, for which she takes pantoprazole. The blood pressure is 100/60 mm Hg, the pulse is 70/min, and the respiratory rate is 12/min. The physical examination reveals pale mucosa and conjunctiva, and bilateral breast tenderness. The LMP was 9 weeks ago. What is the most appropriate next step in the management of this patient?

Beta-HCG levels and a transvaginal ultrasound

Beta-HCG levels and a transabdominal ultrasound

Beta-HCG levels and a pelvic CT

A 69-year-old man is scheduled to undergo radical retropubic prostatectomy for prostate cancer in 2 weeks. He had a myocardial infarction at the age of 54 years. He has a history of GERD, unstable angina, hyperlipidemia, and severe osteoarthritis in the left hip. He is unable to climb up stairs or walk fast because of pain in his left hip. He had smoked one pack of cigarettes daily for 30 years but quit 25 years ago. He drinks one glass of wine daily. Current medications include aspirin, metoprolol, lisinopril, rosuvastatin, omeprazole, and ibuprofen as needed. His temperature is 36.4°C (97.5°F), pulse is 90/min, and blood pressure is 136/88 mm Hg. Physical examination shows no abnormalities. A 12-lead ECG shows Q waves and inverted T waves in leads II, III, and aVF. His B-type natriuretic protein is 84 pg/mL (N < 125). Which of the following is the most appropriate next step in management to assess this patient's perioperative cardiac risk?

Radionuclide myocardial perfusion imaging

24-hour ambulatory ECG monitoring

A pathologist receives a patient sample for analysis. Cells in the sample are first labeled with fluorescent antibodies and then passed across a laser beam in a single file of particles. The light scatter and fluorescent intensity of the particles are plotted on a graph; this information is used to characterize the sample. This laboratory method would be most useful to establish the diagnosis of a patient with which of the following?

Pancytopenia and deep vein thrombosis with intermittent hemoglobinuria

Ventricular septal defect and facial dysmorphism with low T-lymphocyte count

Painless generalized lymphadenopathy with monomorphic cells and interspersed benign histiocytes on histology

Multiple opportunistic infections with decreased CD4 counts

Vesicular lesions with dermatomal distribution and dendritic corneal ulcers

A 55-year-old man presents to the physician with tiredness, lethargy, bone pain, and colicky right abdominal pain for 1 month. He has no comorbidities. He does not have any significant past medical history. His height is 176 cm (5 ft 7 in), weight is 88 kg (194 lb), and his BMI is 28.47 kg/m2. The physical examination is normal, except for mild right lumbar region tenderness. Laboratory studies show: Hemoglobin 13.5 g/dL Serum TSH 2.2 mU/L Serum calcium 12.3 mg/dL Serum phosphorus 1.1 mg/dL Serum sodium 136 mEq/L Serum potassium 3.5 mEq/L Serum creatinine 1.1 mg/dL Urine calcium Elevated An ultrasound of the abdomen reveals a single stone in the right ureter without hydroureteronephrosis. Clinically, no evidence of malignancy was observed. An X-ray of the long bones reveals diffuse osteopenia with subperiosteal bone resorption. The serum parathyroid hormone level is tested and it is grossly elevated. What is the most appropriate next step in his management?

99mTc sestamibi scan with ultrasound of the neck

A 27-year-old man presents to the emergency department with back pain. The patient states that he has back pain that has been steadily worsening over the past month. He states that his pain is worse in the morning but feels better after he finishes at work for the day. He rates his current pain as a 7/10 and says that he feels short of breath. His temperature is 99.5°F (37.5°C), blood pressure is 130/85 mmHg, pulse is 80/min, respirations are 14/min, and oxygen saturation is 99% on room air. On physical exam, you note a young man who does not appear to be in any distress. Cardiac exam is within normal limits. Pulmonary exam is notable only for a minor decrease in air movement bilaterally at the lung bases. Musculoskeletal exam reveals a decrease in mobility of the back in all four directions. Which of the following is the best initial step in management of this patient?

Radiography of the lumbosacral spine

Nuclear medicine imaging — USMLE Lesson

Fundamentals - Radioactive Reporters

Radiotracer: A radioisotope (e.g., Tc-99m) attached to a pharmaceutical that targets specific tissues or physiological processes.
Key Emissions:
- Alpha ($α$, $^4_2$He nucleus): High energy, but very low tissue penetration. Not used for diagnostic imaging.
- Beta ($β$, electron/positron): Moderate penetration. Positron ($β^+$) emission is the basis for PET imaging.
- Gamma ($γ$, photon): High penetration, easily exits the body. Ideal for external imaging with a gamma camera (SPECT).
📌 Gamma Gives Good imaging.

⭐ Technetium-99m (Tc-99m) is the most common radioisotope for SPECT imaging due to its ideal 140 keV gamma emission and 6-hour half-life.

Penetration of Alpha, Beta, and Gamma Radiation

SPECT vs. PET - Functional Fireworks

Feature	SPECT (Single-Photon Emission CT)	PET (Positron Emission Tomography)
Principle	Detects single gamma rays from a radiotracer.	Detects two gamma rays from positron-electron annihilation.
Tracers	Gamma emitters (e.g., Technetium-99m, $^{99m}$Tc).	Positron emitters (e.g., $^{18}$F-FDG).
Resolution	Lower spatial resolution.	Higher spatial resolution & sensitivity.
Cost	Less expensive, more available.	More expensive, less available.
Uses	* Bone scans (metastases) * Myocardial perfusion * Brain (seizure foci)	* Oncology (staging, monitoring) * Myocardial viability * Neurology (dementia)

⭐ PET/CT with $^{18}$F-FDG is a cornerstone of oncology imaging. Malignant cells exhibit high glucose metabolism (Warburg effect), leading to intense FDG uptake, which helps differentiate tumors from benign lesions and locate metastases.

High-Yield Applications - A Scan for All Seasons

Cardiology (Myocardial Perfusion): SPECT with Thallium-201 or $Tc^{99m}$-sestamibi to detect ischemia/infarction. Compares rest vs. stress (exercise/pharmacologic) images.
Pulmonology (V/Q Scan): For pulmonary embolism diagnosis, especially when CT angiography is contraindicated (e.g., renal failure, pregnancy). Uses $Xe^{133}$ for ventilation & $Tc^{99m}$-MAA for perfusion.
Endocrinology:
- Thyroid Scan: $I^{123}$ uptake assesses function. "Hot" nodules are hyperfunctioning (usually benign); "cold" nodules have ↓uptake (higher cancer risk).
- Parathyroid Scan: $Tc^{99m}$-Sestamibi localizes hyperfunctioning adenomas.
Gastrointestinal:
- HIDA Scan: $Tc^{99m}$-iminodiacetic acid analogs. Non-visualization of the gallbladder suggests cholecystitis.
- GI Bleed Scan: $Tc^{99m}$-labeled RBCs detect active extravasation.
Oncology/MSK:
- Bone Scan: $Tc^{99m}$-MDP (methylene diphosphonate) for metastatic disease, fractures, osteomyelitis. 📌 MDP = "Marrow/Disease Pointer".
- PET Scan: $F^{18}$-FDG shows metabolic activity. Used for cancer staging and monitoring treatment response.

⭐ A V/Q scan showing a "mismatched defect" (perfusion defect without a corresponding ventilation defect) is highly specific for a pulmonary embolism.

V/Q scan showing mismatched defect in pulmonary embolism

Radiation Safety - Handle With Care

ALARA Principle: As Low As Reasonably Achievable. Minimize radiation dose by optimizing:
- Time: ↓ exposure time.
- Distance: ↑ distance from the source.
- Shielding: Use lead aprons & barriers.
Contraindications: Pregnancy is an absolute contraindication. Breastfeeding is a relative one (requires temporary cessation).
Post-Scan Advice: Hydrate to accelerate radiotracer excretion. Limit close contact with children & pregnant women.

⭐ A patient's radiation dose from a typical nuclear scan (e.g., bone scan) is comparable to a few years of natural background radiation.

Radiation Safety Principles: Time, Distance, Shielding

High‑Yield Points - ⚡ Biggest Takeaways

PET scans use FDG to find metabolically active tissues like tumors or inflammation.

HIDA scans diagnose acute cholecystitis when the gallbladder is not visualized.

V/Q scans identify pulmonary embolism through a ventilation-perfusion mismatch.

Bone scans are highly sensitive for bony metastases, fractures, and osteomyelitis.

On a thyroid scan, "cold" nodules have a higher malignancy risk than "hot" nodules.

Gallium scans help localize inflammation and tumors like lymphoma and sarcoidosis.

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