A new PET scanner with semiconductor detectors enables better identification of intratumoral inhomogeneity.
An autoradiography method revealed intratumoral inhomogeneity in various solid tumors. It is becoming increasingly important to estimate intratumoral inhomogeneity. However, with low spatial resolution and high scatter noise, it is difficult to detect intratumoral inhomogeneity in clinical settings. We developed a new PET system with CdTe semiconductor detectors to provide images with high spatial resolution and low scatter noise. Both phantom images and patients' images were analyzed to evaluate intratumoral inhomogeneity.


METHODS
This study was performed with a cold spot phantom that had 6-mm-diameter cold sphenoid defects, a dual-cylinder phantom with an adjusted concentration of 1:2, and an "H"-shaped hot phantom. These were surrounded with water. Phantom images and (18)F-FDG PET images of patients with nasopharyngeal cancer were compared with conventional bismuth germanate PET images. Profile curves for the phantoms were measured as peak-to-valley ratios to define contrast. Intratumoral inhomogeneity and tumor edge sharpness were evaluated on the images of the patients.


RESULTS
The contrast obtained with the semiconductor PET scanner (1.53) was 28% higher than that obtained with the conventional scanner (1.20) for the 6-mm-diameter cold sphenoid phantom. The contrast obtained with the semiconductor PET scanner (1.43) was 27% higher than that obtained with the conventional scanner (1.13) for the dual-cylinder phantom. Similarly, the 2-mm cold region between 1-mm hot rods was identified only by the new PET scanner and not by the conventional scanner. The new PET scanner identified intratumoral inhomogeneity in more detail than the conventional scanner in 6 of 10 patients. The tumor edge was sharper on the images obtained with the new PET scanner than on those obtained with the conventional scanner.


CONCLUSIONS
These phantom and clinical studies suggested that this new PET scanner has the potential for better identification of intratumoral inhomogeneity, probably because of its high spatial resolution and low scatter noise.
Shiga
Tohru
T
Department of Nuclear Medicine, School of Medicine, Hokkaido University, Sapporo, Hokkaido, Japan. tshiga@med.hokudai.ac.jp
Morimoto
Yuichi
Y
Kubo
Naoki
N
Katoh
Norio
N
Katoh
Chietsugu
C
Takeuchi
Wataru
W
Usui
Reiko
R
Hirata
Kenji
K
Kojima
Shinichi
S
Umegaki
Kikuo
K
Shirato
Hiroki
H
Tamaki
Nagara
N
D000328:Adult; D000368:Aged; D001729:Bismuth; D019187:Cadmium Compounds; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D005260:Female; D005857:Germanium; D005947:Glucose / Q000378:metabolism; D006801:Humans; D008297:Male; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology*; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation*; D012666:Semiconductors / Q000295:instrumentation*; D013691:Tellurium; D013997:Time Factors
D019187:Cadmium Compounds; D005857:Germanium; C042364:bismuth germanium oxide; D005947:Glucose; D013691:Tellurium; C028337:cadmium telluride; D001729:Bismuth