Thesis

44 Part I Chapter 2 to assist in localizing anomalies seen on the whole-body images and to improve lesion contrast. In oncology, tomographic images should be used not only for better localization of unclear lesions on planar images but also in patients with high pre-test probability for having bone metastases (for example bone metastases in patients with increased tumour marker levels, recurrent cancer, advanced tumours that predominantly metastasize to bone etc. [22, 52]. SPECT imaging should be performed as recommended by the gamma-camera manufacturer. In a typical acquisition protocol for a dual-headed gamma camera with the detector heads oriented in 180° geometry, a total of 60 or 64 frames per detector head, each with duration of 10 to 30 seconds are acquired over 360°, into a 128x128 matrix (pixel size, 4.6x4.6 mm). An equivalent total number of counts should be acquired if continuous acquisition is used. SPECT/CT images are acquired using a multimodality camera that combines a gamma camera and a multi-slice spiral or flat panel/cone beam CT (currently with 1, 2, 4, 6 or 16 slices). The CT is performed immediately before or after the SPECT acquisition. The acquisition protocols are specific to each type of machine. The CT component can be performed either for attenuation correction and anatomic localization or as an optimized diagnostic CT scan [53]. If the CT scan is obtained for attenuation correction and anatomic localization only, the use of a lowmilliampereseconds setting is recommended to decrease the radiation dose to the patient. However, significant differences in operating characteristics between types of scanner exist, hampering recommendations on absolute values of milliampereseconds. Operators should be aware of the characteristics particular to their scanner and understand the range of settings that are consistent with meeting the required image quality and reference dose values. The use of intravenous iodinated contrast is generally not required and MRI is preferred to assess soft tissue disease. The image matrix size is 512x512, with a tube voltage of 80 - 130 kV and intensitytime product of 2.5 to 300 mAs, depending on the anatomical region that is being scanned and the dose reduction software that is used. The pitch can range from 1 to 2 and the slice thickness is generally 0.33-2.0mm for scanning extremities and 0.33 to 5 mm for the spine (table 2). The final image is obtained after applying a high resolution filter. The SPECT/CT acquisitionmay span a single field of view (FOV), usually covering a region of 40 cm, or can include multiple contiguous or separate FOV

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