Voltage (KV) and current (MAS) optimization for gamma ray attenuation correction by computed tomography in spect

Nuclear Medicine is a scientific and clinical discipline involving the use of radiopharmaceuticals composed of radionuclides and biological agents providing the radionuclides to localize to specific organs or sites of disease, in the diagnosis and treatment of disease. The imaging procedure is based on detection of gamma rays emitted by the radionuclide portion of the radiopharmaceuticals administered to the patients' body by gamma camera devices having the ability of acquiring Single Photon Emission Computed Tomography (SPECT) images. For providing anatomical correlations, hybrid SPECT-CT devices designed by the adding computed tomography (CT) device to a conventional single-photon emission computed tomography (SPECT) device, are used. Anatomic correlation is performed by using CT images from CT portion of the SPECT-CT device. The SPECT/CT-technology enables a direct correlation of anatomic information and functional information by fusion of the SPECT and CT images, resulting in better localization and definition of scintigraphic findings. Besides anatomic correlation, SPECT-CT devices also allow patient-specific attenuation correction and the CT images are also used for attenuation correction of SPECT Data. The attenuation correction is performed by using the Hounsfield Unit (HU) values of the CT images and the SPECT count values are corrected by taking into consideration the attenuation as gamma rays travel through the tissues. However, the introduction of CT in the nuclear diagnostic process results in a appreciable increase of the patient dose. In particular, radionuclide therapy regimens, at which SPECT-CT is performed 4 to 5 times for dosimetry studies, the radiation dose from CT examinations becomes more significant. In this context, the voltage (kV) and current (mAs) parameters should be optimized to minimize the additional patient dose. In this study, it is aimed to investigate optimum voltage (kV) and current (mAs) values to achieve the lowest radiation dose to the patients, without compromising image quality and accuracy of dosimetry results. As a result of the experiments performed with Mediso Anyscan SC SPECT-CT device and Jaszczak fantom for five different radioisotopes, by varying the current and voltage parameters in the ranges of 10-300 mAs and 80-140 kV, respectively, it is found that the correction factors does not change significantly with current and voltage in these ranges. The correction factors obtained with the highest voltage (kV) and current (mAs) values are comparable to each other. For this reason, it is concluded that the use of the lowest voltage (kV) and current (mAs) values for SPECT-CT imaging, especially for post-treatment dosimetry procedures, is more appropriate for patient's radiation safety. Keywords: SPECT-CT, Attenuation Correction, Hounsfield Unit