Reporting Nuclear Medicine Studies

---
name: reporting-nuclear-medicine-studies
language: en
description: 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.
tags:
  - reporting
  - radiology
metadata:
  author: casemark
  practice_areas:
    - Radiology
    - Diagnostic Imaging
  document_types:
    - Report
  skill_modes:
    - Reporting
---

# Reporting Nuclear Medicine Studies

Structures nuclear medicine and PET/CT interpretation with SUV measurement and staging correlation.

## Why This Skill Exists

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.

---

## Checkpoint A: Pre-Draft Intake (Mandatory)

1. **What nuclear medicine study is being interpreted?** (Default: Identify — PET/CT, bone scan, thyroid scan, V/Q scan, renal scan, HIDA/hepatobiliary, MUGA, etc.)
2. **What radiotracer was used?** (Default: 18F-FDG for PET/CT — specify for other studies)
3. **What is the clinical indication?** (Default: Staging, restaging, treatment response, surveillance — obtain specific clinical question)
4. **Are prior nuclear medicine studies available?** (Default: No — obtain for comparison)
5. **Is the patient's blood glucose level documented?** (Default: Required for FDG PET — must be <200 mg/dL)
6. **What is the patient's oncologic history/staging?** (Default: Obtain cancer type, treatment history, current staging)
7. **Was diagnostic CT performed concurrently or is this a low-dose attenuation-correction CT only?** (Default: Verify CT technique)

### Documents to Request

- Nuclear medicine images (all standard views and reconstructions)
- Blood glucose level at time of FDG injection
- Radiotracer type, dose, injection-to-scan time
- Prior nuclear medicine studies for comparison
- Recent cross-sectional imaging (CT, MRI) for correlation
- Oncologic staging history and treatment timeline
- Relevant tumor markers and clinical notes

---

## Step 1: Technical Assessment

### FDG PET/CT Technical Quality

| 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 |

### Other Nuclear Medicine Technical Factors

| 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 |

---

## Step 2: PET/CT Interpretation — Systematic Approach

### SUV Measurement Technique

| 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 |

### Physiologic FDG Uptake (Normal — Do Not Misinterpret)

| 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) |

### PET/CT Report Structure — Organ-System Review
1. **Head/Neck**: Brain, cervical lymph nodes, thyroid, salivary glands
2. **Chest**: Lungs, mediastinal/hilar lymph nodes, pleura, chest wall
3. **Abdomen/Pelvis**: Liver, spleen, adrenals, kidneys, GI tract, mesenteric/retroperitoneal lymph nodes, pelvis
4. **Musculoskeletal**: Bones (focal vs. diffuse uptake), joints (degenerative vs. inflammatory)
5. **Skin/Subcutaneous**: Injection site, skin metastases

---

## Step 3: Disease-Specific Reporting Criteria

### Lymphoma — Deauville 5-Point Scale (Lugano Classification)

| 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.

### Bone Scan Interpretation

| 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 |

### V/Q Scan — Modified PIOPED II Criteria

| 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% |

---

## Step 4: Report Structure

### Standard Nuclear Medicine Report Format

**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**:
1. Most clinically significant finding addressing the clinical question
2. Disease-specific classification (Deauville score, Lugano response category)
3. Incidental findings with recommendations
4. Comparison summary with prior study

---

## Step 5: Treatment Response Assessment

### PET Response Criteria — PERCIST 1.0

| 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 |

---

## Checkpoint B: Post-Draft Alignment (Mandatory)

1. Is the radiotracer and technical quality documented (glucose, uptake time)?
2. Are SUV measurements provided for all significant findings?
3. Is physiologic uptake distinguished from pathology?
4. Is the appropriate disease-specific classification applied (Deauville, PERCIST)?
5. Are prior studies compared with SUV trending?

---

## Quality Audit

- [ ] Radiotracer, dose, and injection-to-scan time are documented
- [ ] Blood glucose level is recorded for FDG PET studies
- [ ] CT technique (diagnostic vs. low-dose) is specified
- [ ] SUVmax is reported for all significant lesions
- [ ] Physiologic uptake is recognized and not over-interpreted
- [ ] Disease-specific scoring is applied (Deauville, PERCIST, modified PIOPED)
- [ ] Reference structure SUVs (mediastinal blood pool, liver) are documented for lymphoma
- [ ] Comparison with prior PET studies includes SUV trending
- [ ] New lesions are explicitly identified and flagged
- [ ] Incidental findings are managed per ACR recommendations
- [ ] Report addresses the specific clinical question in the impression
- [ ] Technical limitations (misregistration, extravasation, elevated glucose) are noted
- [ ] Bone scan flare response is considered in post-treatment context

---

## Guidelines

1. Always document blood glucose level for FDG PET — studies performed with glucose >200 mg/dL have reduced sensitivity and should prompt consideration of rescanning.
2. Report SUVmax for all significant lesions; use SULpeak when applying PERCIST criteria for treatment response.
3. Correlate every PET finding with the CT component — FDG-avid findings without a CT correlate require further investigation, not dismissal.
4. Apply the Deauville 5-point scale for lymphoma interim and end-of-treatment PET; always report mediastinal blood pool and liver reference SUVs.
5. Recognize physiologic variants (brown fat, post-G-CSF marrow activation, GI peristalsis) to avoid false-positive interpretations.
6. For V/Q scans, use the modified PIOPED II criteria and provide a probability category — vague interpretations like "indeterminate" should prompt recommendation for CTA.
7. Compare uptake-time-matched studies when trending SUV; a 90-minute uptake-time PET is not directly comparable to a 60-minute study.