Normal SUV Range for Thyroid and Full Body I-131 Scan
For I-131 thyroid imaging, standardized uptake values (SUVs) are not typically used for clinical interpretation; instead, qualitative visual assessment of uptake patterns is the standard approach recommended by clinical guidelines.
Standard Approach to I-131 Thyroid Imaging
- I-131 whole-body scintigraphy is recommended for post-treatment evaluation of differentiated thyroid cancer patients after thyroidectomy and radioiodine ablation 1
- These scans are interpreted qualitatively through visual assessment rather than through SUV quantification 1
- For patients who have undergone thyroidectomy and radioiodine ablation, any visible uptake in the thyroid bed on follow-up scans may indicate residual thyroid tissue 1
Thyroid Uptake Measurements
- In diagnostic thyroid scanning, uptake is typically measured as a percentage of the administered dose rather than as an SUV 1
- The standard approach for radioiodine uptake measurement is expressed as percentage uptake at specific time points (typically 24 hours) 2
- For treatment planning in hyperthyroidism, the formula used is based on microcuries per gram of thyroid tissue divided by the percentage of radioiodine uptake 2
Clinical Applications and Interpretation
- I-131 whole-body scans are performed after radioiodine therapy to evaluate for residual disease or metastases 3, 1
- In differentiated thyroid cancer follow-up, the scan results are interpreted alongside serum thyroglobulin measurements, which serve as a biochemical marker of residual or recurrent disease 3
- For thyroid remnant ablation, a fixed dose approach (using standard doses like 50 or 100 mCi) is often used rather than calculations based on SUV 3
Alternative Imaging Approaches
- FDG-PET/CT is sometimes used in thyroid cancer patients with elevated thyroglobulin but negative I-131 scans 4
- When FDG-PET/CT is used, SUV measurements become relevant, with SUVmax values over 4.5 being significant for detecting recurrent disease 4
- For routine surveillance of low-risk patients without suspicion for recurrence and normal thyroid ultrasound, I-131 whole-body scanning is not utilized 1
Important Considerations
- The quality of I-123 imaging is superior to I-131 for diagnostic scanning, with better visualization of uptake foci 5
- There is concern about "thyroid stunning" where diagnostic doses of I-131 may decrease further radioiodine uptake during subsequent therapy 6
- Ultrasound remains the preferred first-line imaging for early follow-up after treatment of differentiated thyroid cancer 1