Takafumi Ishitsu

Development of a 3D Brain PET Scanner Using CdTe Semiconductor Detectors and Its First Clinical Application

Targeting improved spatial resolution, a three-dimensional positron-emission-tomography (PET) scanner employing CdTe semiconductor detectors and using depth-of-interaction (DOI) information was developed, and its physical performance was evaluated. This PET scanner is the first to use semiconductor detectors dedicated to the human brain and head-and-neck region. Imaging performance of the scanner used for 18F -fluorodeoxy glucose (FDG) scans of phantoms and human brains was evaluated. The gantry of the scanner has a 35.0-cm-diameter patient port, the trans-axial field of view (FOV) is 31.0 cm, and the axial FOV is 24.6 cm. The energy resolution averaged over all detector channels and timing resolution were 4.1% and 6.8 ns (each in FWHM), respectively. Spatial resolution measured at the center of FOV was 2.3-mm FWHM-which is one of the best resolutions achieved by human PET scanners. Noise-equivalent count ratio (NEC2R) has a maximum in the energy window of 390 to 540 keV and is 36 kcps/Bq/cm3 at 3.7 kBq/cm3 . The sensitivity of the system according to NEMA 1994 was 25.9 cps/Bq/cm3. Scatter fraction of the scanner is 37% for the energy window of 390 to 540 keV and 23% for 450 to 540 keV. Images of a hot-rod phantom and images of brain glucose metabolism show that the structural accuracy of the images obtained with the semiconductor PET scanner is higher than that possible with a conventional Bismuth Germanium Oxide (BGO) PET scanner. In addition, the developed scanner permits better delineation of the head-and-neck cancer. These results show that the semiconductor PET scanner will play a major role in the upcoming era of personalized medicine.

Basic Performance Test of a Prototype PET Scanner Using CdTe Semiconductor Detectors

A prototype positron emission tomography (PET) scanner using CdTe semiconductor detectors was developed, and its initial evaluation was conducted. The scanner was configured to form a single detector ring with six separated detector units, each having 96 detectors arranged in three detector layers. The field of view (FOV) size was 82 mm in diameter. Basic physical performance indicators of the scanner were measured through phantom studies and confirmed by rat imaging. The system-averaged energy resolution and timing resolution were 5.4% and 6.0 ns (each in FWHM) respectively. Spatial resolution measured at FOV center was 2.6 mm FWHM. Scatter fraction was measured and calculated in a National Electrical Manufacturers Association (NEMA)-fashioned manner using a 3-mm diameter hot capillary in a water-filled 80-mm diameter acrylic cylinder. The calculated result was 3.6%. Effect of depth of interaction (DOI) measurement was demonstrated by comparing hot-rod phantom images reconstructed with and without DOI information. Finally, images of a rat myocardium and an implanted tumor were visually assessed, and the imaging performance was confirmed.

Development of edge-on type CdTe detector module for gamma camera

The detector module using CdTe with edge-on configuration was developed. The pixel pitch is 1.4 mm, and 1024 pixels constitute the field of view of 45 mm square. The CdTe crystals sandwich thin circuit boards to form CdTe cards, and 16 CdTe cards are mounted on the module. The intrinsic energy resolution of 4.4% (FWHM) was achieved with Tc-99m at CdTe temperature of 25 °C. It remains 5.1% at 40 °C, which implies the possibility of air-cooling system. Uniformity and count-rate performance were also evaluated.

Physical performance of a prototype 3D PET scanner using CdTe detectors

We developed a prototype 3D PET scanner that uses CdTe semiconductor detectors. The scanner is dedicated to human brain imaging. A semiconductor detector should have advantages when used as a PET detector (e.g. good quantitative imaging and high-spatial resolution). The detectors incorporate three important technical features: stacked crystals, no contact with the board, and direct soldering onto the board. Our scanner comprises 18 detector units with a 350-mm-diameter patient port that has a transaxial field of view of 310 mm and an axial field of view of 250 mm. We demonstrated the scanner had a timing resolution of 6.8 ns (FWHM), an energy resolution of 4.1% (FWHM), and a spatial resolution such that hot rods down to 2.5 mm in diameter were visually separated. These results showed that our scanner should produce quantitative imaging with a high-spatial resolution.

Development of a Prototype 3D PET Scanner Using Semiconductor Detectors and Depth of Interaction Information

A prototype brain positron emission tomography (PET) scanner using semiconductor detectors and depth of inleraclion (DOI) information has been developed to achieve high spatial resolulion and reduced scalier fraction. At the first step of the development, we created a two-dimensional prololype PET scanner composed of a single-slice full-ring detector unit to confirm the feasibility of the basic technologies that are necessary lo realize a semiconductor PET scanner. Through phantom and small-animal studies, the feasibility of the semiconductor PET was confirmed and the results showed that the semiconductor PET could produce quantitative imaging with high spatial resolution. Based on these achievements, a prototype brain PET scanner was developed to demonstrate the high spatial resolution and quantitative imaging capability required in human imaging.