INFLUENCE OF SOURCE-TO- COLLIMATOR DISTANCE ON IMAGE QUALITY IN SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY (SPECT): A PHANTOM STUDY

INFLUENCE OF SOURCE-TO- COLLIMATOR DISTANCE ON SPECT IMAGE QUALITY

Abstract

Introduction: Source-to-collimator distance is one of the physical factor that can affect the quality of the image generated in Single Photon Emission Computed Tomography (SPECT). It makes the use of the gamma camera in detecting the gamma rays emitted from the subject. Therefore, this study was designed to investigate the influence of source-to- collimator distance on image quality in SPECT in terms of uniformity of uniform regions, hot and cold regions detectability, perceived image quality, contrast, signal- to-noise ratio (SNR) as well as the count profile of uniform, hot and cold regions. Methods: R.A. Carlson acrylic SPECT cylindrical phantom by using of Philips ADAC Forte dual head gamma camera with parallel- hole, low energy high resolution (LEHR) collimator. Five different settings of detector radius were applied to the phantom which were 26cm, 27cm, 28cm, 29cm and 30cm. For each detector radius, the table-to-collimator distance was measured and the phantom-to-collimator distance was calculated by subtracting the phantom outer diameter (OD) from the table-to-collimator distance. Reconstruction of the images was done by using filtered back-projection (FBP) in conjunction with Butterworth filter with cut off frequency 0.35 cycle/cm and order 5. The reconstructed images were evaluated qualitatively via perceived image quality and count profile analysis, and quantitatively via contrast and signal-to-noise ratio (SNR) calculation. Results: it was observed that was degradation in uniformity, hot and cold regions detectability, sharpness, shape and hot regions pair separation. For quantitative analysis, the contrast are decreased with the phantom-to-collimator distance in most of the hot and cold regions while in signal-to-noise ratio (SNR), there is reduction for hot and cold regions. Conclusion: In conclusion, the image quality of hot and cold regions detectability, sharpness, shape, hot regions pair separation, contrast and signal-to-noise ratio (SNR) are degraded as the phantom-to-collimator distance increases.

KEYWORDS: SPECT, Image quality, Source-to-Collimator distance, Spatial resolution