Structures nuclear medicine and PET/CT interpretation with SUV measurement and staging correlation. Use when reading nuclear medicine studies, interpreting PET findings, or documenting radiotracer uptake.
Structures nuclear medicine and PET/CT interpretation with SUV measurement and staging correlation.
Nuclear medicine studies provide unique functional and metabolic information that complements anatomic imaging. PET/CT with 18F-FDG is the cornerstone of oncologic staging, treatment response assessment, and surveillance. Other nuclear medicine studies — bone scans, thyroid scans, V/Q scans, hepatobiliary scans, renal scans — each have specific interpretation criteria, quantitative thresholds, and reporting standards. Misinterpreting physiologic radiotracer uptake as pathology, failing to correlate PET findings with CT anatomy, or omitting SUV measurements undermines the clinical utility of these studies.
The ACR-SNMMI Practice Parameter for PET/CT and general nuclear medicine mandates structured reporting with quantitative measurements, clinical correlation, and explicit comparison with prior studies. The Deauville 5-point scale is the international standard for interim PET response in lymphoma, and the Lugano classification integrates PET findings into lymphoma staging. For PE evaluation, the PIOPED II criteria and modified PIOPED criteria define V/Q interpretation standards. This skill provides the systematic framework for interpreting and reporting nuclear medicine studies across all major exam types.
| Parameter | Standard | Impact if Suboptimal |
|---|---|---|
| Blood glucose | <200 mg/dL (ideally <150) | Elevated glucose competes with FDG; decreases tumor uptake, increases muscle uptake |
| Uptake time | 60 ± 10 minutes | Inconsistent uptake times affect SUV comparability between studies |
| Patient fasting | ≥4–6 hours | Non-fasting increases physiologic GI and muscle uptake |
| CT technique | Diagnostic vs. low-dose AC only | Low-dose CT limits anatomic correlation; document limitation |
| Misregistration | PET-CT alignment | Respiratory motion causes misregistration at diaphragm; note if findings are affected |
| Injection quality | Extravasation check | Extravasation at injection site reduces circulating activity; document and note impact |
| Study | Key Technical Factor |
|---|---|
| Bone scan | 2–3 hour delay post-injection; adequate hydration and voiding |
| V/Q scan | Adequate Tc-99m MAA particles (200,000–700,000); Xe-133 or Tc-99m DTPA for ventilation |
| Thyroid scan | TSH level (elevated for whole-body I-131); iodine-free diet if I-131 |
| Renal scan (MAG3) | Adequate hydration; Lasix timing for diuretic renogram |
| HIDA | Fasting ≥4 hours; morphine augmentation if needed |
| Metric | Definition | Clinical Use |
|---|---|---|
| SUVmax | Maximum SUV within a VOI | Most commonly reported; highest single-voxel value |
| SUVpeak | Average SUV in a 1 cm³ sphere centered on hottest voxel | Less susceptible to noise than SUVmax |
| SUVmean | Average SUV across the entire VOI | Used in research; less common clinically |
| SULpeak | Lean-body-mass-corrected SUVpeak | Recommended for treatment response; normalizes for body composition |
| MTV | Metabolic tumor volume | Total volume of metabolically active tumor |
| TLG | Total lesion glycolysis (SUVmean × MTV) | Quantifies total metabolic burden |
| Location | Pattern | Mimics |
|---|---|---|
| Brain | Intense cortical uptake | — (baseline reference) |
| Tonsillar/Waldeyer ring | Symmetric ring of uptake | Lymphoma (asymmetric = suspicious) |
| Vocal cords | Bilateral, symmetric, post-vocalization | Laryngeal tumor (unilateral = suspicious) |
| Myocardium | Variable (fasting state reduces) | Cardiac tumor (focal = suspicious) |
| GI tract (stomach, colon) | Variable physiologic; peristaltic pattern | GI malignancy (focal, intense = suspicious) |
| Urinary tract | Excreted FDG in collecting system, bladder | Urothelial tumor (wall-based uptake) |
| Bone marrow | Diffuse after chemotherapy or G-CSF | Marrow involvement (focal = suspicious) |
| Brown fat | Bilateral symmetric neck/supraclavicular | Lymphadenopathy (correlate with CT) |
| Score | Uptake Level | Interpretation |
|---|---|---|
| 1 | No uptake | Complete metabolic response (CMR) |
| 2 | Uptake ≤ mediastinal blood pool | CMR |
| 3 | Uptake > mediastinal blood pool but ≤ liver | CMR (for most aggressive lymphomas) |
| 4 | Uptake moderately > liver | Partial metabolic response or progressive disease (context-dependent) |
| 5 | Uptake markedly > liver and/or new lesions | Progressive metabolic disease |
| X | New areas of uptake unlikely related to lymphoma | Document separately |
Reference structures: Measure mediastinal blood pool SUV (aortic arch) and liver SUV (right lobe, avoiding vessels) as internal references at every timepoint.
| Finding | Description | Significance |
|---|---|---|
| Focal increased uptake | Single or multiple discrete foci | Metastasis, fracture, infection, degenerative (correlate with history and location) |
| Superscan | Diffusely increased skeletal uptake with absent renal activity | Diffuse skeletal metastases (prostate, breast) |
| Flare response | Increased uptake on post-treatment scan → improves on subsequent scan | Healing response; not progression |
| Photopenic lesion | Cold defect | Purely lytic metastasis (myeloma, renal cell), avascular necrosis, radiation |
| Category | Criteria | PE Probability |
|---|---|---|
| Normal | No perfusion defects | <5% |
| Very low | Non-segmental perfusion defects; match defects with normal CXR | <10% |
| Low | Small subsegmental V/Q mismatch | 10–30% |
| Intermediate | Difficult to categorize | 30–70% |
| High | ≥2 large segmental mismatched perfusion defects | >80% |
Header: Patient demographics, study type, radiotracer, dose, injection-to-scan time, blood glucose (PET)
Clinical Indication: Specific clinical question with relevant history
Comparison: Prior studies with dates and modality
Technique: Radiotracer, dose, route, uptake time, CT parameters (diagnostic vs. low-dose), fasting status
Findings: Organ-system review with SUV measurements for significant findings; comparison with prior SUV values when available
Impression:
| Category | Criteria |
|---|---|
| CMR (Complete) | Complete resolution of FDG uptake in all lesions; no new FDG-avid lesions |
| PMR (Partial) | ≥30% decrease in SULpeak of target lesion |
| SMD (Stable) | Does not meet CMR, PMR, or PMD criteria |
| PMD (Progressive) | ≥30% increase in SULpeak or new FDG-avid lesions |