In order to predict and improve the performance of pixelated detectors, it is important to understand the optical
properties of the basic unit of the scintillating structure in the detector. To measure one of the essential optical properties,
reflectance, we have used a device composed of a laser and photodiode array. We have also developed an analytical
model of the optical phenomena based on Snell's law and the Fresnel equations to simply analyze measured results and
reflectance parameters at the interface. The computed and experimentally measured results typically have good
agreement, validating the analytical model and measurements. The optical parameters are used as inputs to GEANT4 .
The simulations are then leveraged to optimize an imager design before a prototype is built.
The optical reflectance was measured by using relatively inexpensive samples. A sample has scintillator, glue, and
septum (reflector) layers, and each sample has a different scintillator surface (polished/rough) and/or reflector [ESR
film/aluminum-sputtered (coated) ESR film] condition. A high-refractive-index hemisphere was attached on the top
surface of a sample to increase the maximum incidence angle at the scintillator-glue interface from 27° to 52°. The
sample including ESR film demonstrated average reflectance approximately 1.3 times higher than that from the sample
with aluminum-sputtered ESR film as a reflector, and the polished surface condition showed higher reflectance than the
rough-cut surface condition.
Breast cancer continues to be the most common malignancy of women in the United States. Nuclear imaging techniques such as positron emission tomography (PET) have been widely used for the staging of cancer. The primary limitations of PET for breast cancer diagnosis are the lack of a highly specific radiotracer and the limited
resolution of imaging systems. The sensitivity for detecting small lesions is very low. Many groups are developing positron emission mammography (PEM) systems dedicated for breast imaging using high resolution detectors. Although image resolution is significantly improved compared to whole-body PET systems, the clinical value of
a PEM system is yet to be proven,<sup>3.4</sup> Most PET systems have limitations in imaging tissues near the chest walls and lymph nodes. The proposed system addresses the sampling requirements specific to breast imaging and achieves high resolution in PET images of breast and thorax.
Coronary angiography is unable to define the status of the atheroma, and only measures the luminal dimensions of the blood vessel, without providing information about plaque content. Up to 70% of heart attacks are caused by minimally obstructive vulnerable plaques, which are too small to be detected adequately by angiography. We have developed an intravascular imaging detector to identify vulnerable coronary artery plaques. The detector works by sensing beta or conversion electron radiotracer emissions from plaque-binding radiotracers. The device overcomes the technical constraints of size, sensitivity and conformance to the intravascular environment. The detector at the distal end of the catheter uses six 7mm long by 0.5mm diameter scintillation fibers coupled to 1.5m long plastic fibers. The fibers are offset from each other longitudinally by 6mm and arranged spirally around a guide wire in the catheter. At the proximal end of the catheter the optical fibers are coupled to an interface box with a snap on connector. The interface box contains a position sensitive photomultiplier tube (PSPMT) to decode the individual fibers. The whole detector assembly fits into an 8-French (2.7 mm in diameter) catheter. The PSPMT image is further decoded with software to give a linear image, the total instantaneous count rate and an audio output whose tone corresponds to the count rate. The device was tested with F-18 and Tl-204 sources. Spectrometric response, spatial resolution, sensitivity and beta to background ratio were measured. System resolution is 6 mm and the sensitivity is >500 cps / micrometers Ci when the source is 1 mm from the detector. The beta to background ratio was 11.2 for F-18 measured on a single fiber. The current device will lead to a system allowing imaging of labeled vulnerable plaque in coronary arteries. This type of signature is expected to enable targeted and cost effective therapies to prevent acute coronary artery diseases such as: unstable angina, acute myocardial infarction, and sudden cardiac death.