PET Clinical Imaging Procedures
What this domain tests
Clinical PET questions test patient selection and preparation, acquisition parameters, normal biodistribution, semiquantitative analysis, and recognition of artifacts. The focus is safe, diagnostic FDG PET/CT and common alternative agents.
Core rules
- Verify fasting, glucose, pregnancy/breastfeeding status, and ability to lie still. Document height and weight because SUV is weight-normalized. Place IV access without excess activity in the field.
- After injection, patients rest quietly in a warm room for 45–60 minutes; talking, chewing, and exercise increase muscle and salivary uptake. Ask the patient to void before scanning.
- Typical oncology acquisition is from skull base to mid-thigh (or vertex to toes for melanoma), arms raised, with CT used for attenuation correction and anatomic localization. PET bed times are usually 2–3 minutes depending on protocol and scanner.
- Normal uptake: brain cortex, myocardium (variable), liver, spleen, bowel, kidneys, ureters, bladder, Waldeyer ring, salivary glands. Liver uptake is a common reference.
- SUV = lesion activity concentration (Bq/mL) ÷ (decay-corrected injected dose (Bq)/patient mass (g)). SUVmax is sensitive to noise and ROI choice; compare same protocol and uptake time.
Worked example
A lesion measures 18,500 Bq/mL. The decay-corrected dose at scan time is 253 MBq and the patient weighs 70 kg. Dose per gram = 253,000,000/70,000 = 3,614 Bq/g. SUV = 18,500/3,614 ≈ 5.1. If the scan is delayed, FDG decays but so does the denominator if corrected; inconsistent correction changes SUV.
Traps
Do not compare SUVs from different uptake times or glucose states. Misregistration from breathing or patient motion creates false hot or cold spots after attenuation correction. Metal, contrast, and pacemakers can produce CT artifacts that propagate into PET.