# Time-of-Flight PET/CT Imaging of Ga-68-Dotatate: Normal Pattern, SUV Quantification, and Differences from Non-Time-of-Flight Imaging

## TL;DR

This study compares Ga-68-dotatate SUV max values using TOF and non-TOF PET/CT imaging to establish a normal database and highlight differences in uptake measurements.

## Contribution

Provides the first normal SUV max database for Ga-68-dotatate using TOF PET/CT and quantifies the differences compared to non-TOF imaging.

## Key findings

- TOF SUV max was higher for most structures compared to non-TOF, with the largest increases in adrenals and pancreas.
- Abnormal lesions showed approximately 1.8 times higher SUV max with TOF compared to non-TOF.
- TOF imaging improved target-to-background ratios visually.

## Abstract

Purpose
 The biodistribution of gallium-68-dotatate (Ga-68-dotatate) and standardized uptake values (SUVs) using non-time-of-flight (TOF) positron emission tomography/computed tomography (PET/CT) cameras is well established. However, with the eventual retirement of older PET cameras and their replacement with newer, highly sensitive TOF PET/CT cameras, where SUV
max
measurements are reportedly higher, updated knowledge of normal SUV
max
range is needed and, to our knowledge, not previously reported. Our objectives are as follows:

To establish normal Ga-68-dotatate TOF SUV
max
database for common structures and to aid the visual detection of abnormalities objectively.

To compare SUV
max
values using the TOF and non-TOF algorithms.

Methods
 Fifty consecutive patients referred routinely to our nuclear medicine service (20 men, 30 women; median age 55 years) with presumed neuroendocrine tumors underwent Ga-68-dotatate scans on a PET-CT camera having capability of reconstructing both TOF/non-TOF images. Region of interests (ROIs) were drawn around 24 normal structures as well as the primary lesion with abnormal radiotracer uptake and SUV
max
was measured. The same ROI was analyzed using both algorithms simultaneously and both TOF and non-TOF SUV
max
values were compared.

Results
 Twelve hundred ROIs were evaluated. Non-TOF Ga-68-dotatate uptake in normal structures was in alignment with previously published studies. As compared to non-TOF, TOF images had better target to background ratios visually. TOF SUV
max
was higher for all structures except for lung and brain. TOF SUV
max
was more than double in adrenals/uncinate process of the pancreas; approximately 1.8 times in abnormal lesions, lymph nodes, pineal gland; and greater than 1.5 times in thyroid, breast, and pancreatic head.

Conclusion
 Normal database of Ga-68-dotatate TOF SUV
max
is provided for common structures to aid visual detection of abnormalities objectively. Overall, TOF SUV
max
measures higher in identical ROIs, with abnormal lesions measuring approximately 1.8 times higher versus non-TOF technology. These findings need to be taken in consideration when comparing patient scans imaged on different PET/CT technologies.