Assessment of Image Quality and Lesion Detectability With Digital PET/CT System

Abstract

Purpose: The aim of this study was to assess image quality and lesion detectability acquired with a digital Positron Emission Tomography/Computed Tomography (PET/CT) Siemens Biograph Vision 600 system. Material and Methods: Consecutive patients who underwent a FDG PET/CT during the first week of use of a digital PET/CT (Siemens Biograph Vision 600) at the nuclear medicine department of the university hospital of Brest were analyzed. PET were realized using list mode acquisition. For all patients, 4 datasets were reconstructed. We determined, according to phantom measurements, an equivalent time acquisition/reconstruction parameters pair of the digital PET/CT corresponding to an analog PET/CT image quality ("analog-like") as reference dataset. We compared the reference dataset with 3 others digital PET/CT reconstruction parameters, allowing a decrease of emission duration: 60, 90, and 120 s per bed position. Three nuclear medicine physicians evaluated independently, for each dataset, overall image quality [Maximal Intensity Projection (MIP), noise, sharpness] using a 4-point scale. Physicians assessed also lesion detection capability by reporting new visible lesions on each digital datasets with their confidence level in comparison with analog-like dataset. Results: Ninety-eight patients were analyzed. Image quality of MIP (IQ_MIP), sharpness (IQ_SHARPNESS), and noise (IQ_NOISE) of all digital datasets (60, 90, and 120 s) were better than those evaluated with analog-like reconstruction. Moreover, digital PET/CT system improved IQ_MIP, IQ_NOISE, and IQ_SHARPNESS whatever the BMI. Lesion detection capability and confidence level were higher for 60, 90, 120 s per bed position, respectively, than for analog-like images. Conclusion: Our study demonstrated an improvement of image quality and lesion detectability with a digital PET/CT system.

Keywords: PET/CT; SiPM; analog detectors; clinical evaluation; image quality.

Figure 1

Contrast recovery measured on original Biograph mCT images and on Biograph Vision “Analog like” images.

Figure 2

MIP images of a 61 years old man, showing improvement of quality, sharpness, and noise when increasing acquisition time [(A-D) from left to right, respectively, 120, 90, 60, and 30 s per bed position].

Figure 3

Coronal CT, PET, and fusion images in the same patient, showing better sharpness of organs, pyelo-ureteral uptakes, and less hepatic noise when increasing acquisition time [(A-D) from top to bottom, respectively, 120, 90, 60, and 30 s per bed position]. We can see noise on the “Analog-like” acquisition which can mimic focal uptake in the right liver (arrow), and which disappears on the other acquisitions.

Figure 4

Axial CT, PET, and fusion images in a 65 years old man, showing a bone focal uptake in T11, on the “Analog-like” acquisition, which disappears when increasing acquisition time, and corresponding actually to noise [(A-D) from top to bottom, respectively, 120, 90, 60, and 30 s per bed position].

Figure 5

Coronal CT, PET, and fusion images in a 48 years old woman, illustrating detectability improvement when increasing acquisition time, with appearance of a focal uptake in left thyroid lobe, which cannot be seen on the “Analog-like” acquisition [(A-D) from top to bottom, respectively, 120, 90, 60, and 30 s per bed position].