Alternative Liver Reference Site for DOTATATE PET When Right Lobe is Absent
When the right hepatic lobe is absent, place a 3 cm spherical volume of interest (VOI) in the left hepatic lobe to obtain the liver SUV mean reference for DOTATATE PET imaging. 1
Primary Recommendation
The left hepatic lobe serves as the appropriate alternative site for SUV mean reference measurements when the right lobe is unavailable. 1 This approach maintains consistency with established PET imaging protocols that specify liver as the optimal internal reference organ for somatostatin receptor imaging. 2
Technical Implementation
VOI Placement Guidelines
Position a spherical VOI with 3 cm diameter in the left lobe of the liver, avoiding any malignancies, organ boundaries, and major vascular structures. 1
Target the medial or lateral segments (segments II, III, or IV) of the left lobe while ensuring adequate parenchyma is captured within the measurement region. 3
Avoid the falciform ligament, which divides the medial and lateral segments of the left lobe, as this anatomical landmark may introduce measurement variability. 3
Why Liver SUL is the Optimal Reference
Liver SUL (lean body mass-normalized SUV) demonstrates the lowest variance (3.69% ± 1.25%) among all organs with physiological DOTATATE uptake, making it the most reproducible internal reference. 2 This superior reproducibility stems from the liver's larger size and uniform uptake pattern compared to alternative reference organs like spleen or blood pool. 2
The liver's physiological SUV mean on DOTATATE PET typically ranges from 8.05 (range: 3-15) at standard 1-hour imaging, with minimal variation between early and delayed scans. 4 This stability makes liver measurements reliable for calculating tumor-to-normal organ ratios regardless of imaging timepoint. 4
Alternative Reference Options (If Left Lobe Unavailable)
If the left hepatic lobe is also compromised or insufficient for measurement:
Spleen as Secondary Reference
- Mean spleen SUV on DOTATATE PET averages 18 (range: 8.4-36.7) at standard imaging timepoints. 4
- Spleen demonstrates higher variability than liver, with statistically significant changes between early and delayed scans (P < 0.05). 4
- Spleen SUL shows greater variance than liver SUL, making it a less optimal but acceptable alternative. 2
Blood Pool (Descending Aorta) as Tertiary Reference
- Place VOI within the descending thoracic aorta, carefully avoiding the vessel wall where uptake may be elevated due to vascular inflammation. 1
- Blood pool SUV typically measures around 1.6 (SUL around 1.2) in FDG studies, though specific DOTATATE values differ. 1
- Blood pool measurements show acceptable reproducibility with intrapatient variation reference range of -0.8 to 0.9. 5
Critical Caveats and Pitfalls
Normalization Method Matters
Always use SUL (lean body mass normalization) rather than SUVbw (body weight normalization) when possible, as SUL variance is significantly lower than SUVbw variance (p < 0.0001). 2 This difference becomes particularly important in patients with altered body composition. 2
Avoid Common Measurement Errors
Do not include lesions, metastases, or areas of abnormal uptake within the reference VOI, as this will artificially elevate baseline measurements and reduce tumor-to-liver ratios. 1
Ensure the VOI does not extend beyond organ boundaries or include adjacent structures, which introduces partial volume effects and measurement artifacts. 1
Visually verify all semiautomatically generated VOIs, as automated segmentation may fail in patients with anatomical variants or post-surgical changes. 1
Temporal Considerations
DOTATATE uptake shows minimal change between standard (1-1.5 hour) and delayed (2.5-3 hour) imaging in both liver and tumor lesions, unlike FDG imaging where timing significantly affects measurements. 4 However, maintain consistent timing between baseline and follow-up scans for the same patient to minimize variability. 4
Documentation Requirements
Report both the absolute liver SUV mean and the tumor-to-liver ratio in your imaging report, as tumor-to-normal organ ratios provide more robust assessment than absolute SUV values alone. 6, 4 The mean tumor-to-liver ratio on DOTATATE PET ranges from 3.5 for lower-grade lesions to significantly higher values for Krenning score 4 lesions. 6, 4
Comparison with Therapeutic Lu-177 DOTATATE
Be aware that tumor-to-normal organ ratios differ substantially between diagnostic Ga-68 DOTATATE PET and therapeutic Lu-177 DOTATATE SPECT, with significantly higher ratios on Lu-177 SPECT (average TNR liver = 16.9 vs 3.5 on PET). 6 This difference reflects temporal variations in DOTATATE uptake and internalization kinetics rather than imaging modality effects. 6