Thesis

47 The EANM practice guideline for Bone Scintigraphy Table 2. (continued) § CT settings are variable depending on local requirements/protocols/cameras etc. The use of dose reduction features is recommended if available. ‡ Whole-body image acquisition should be considered in case of suspicion of malignancy (metastatic, primary), rheumatoid arthritis, elevated alkaline phosphatase level, metabolic bone disorders, hyperparathyroidism (brown tumours, superscan, soft tissue uptake in lung, stomach, kidneys, heart or pancreas), infectious disease. 4. Image Processing Planar images do not require particular processing. It should be noted that current digital gamma cameras andworkstations allow changing the range of image contrast, improving the diagnostic value of the images. In addition, this allows choosing the optimum contrast for printing the images that will be sent to the requesting clinician. A relative image quantification may be performed on certain areas. In case of SPECT one should take into account the different types of gamma camera and software available. Reconstructions are preferably performed using threedimensional (3D) iterative ordered subset expectation maximization algorithm (OSEM), including classical corrections for attenuation and scatter, and nowadays also resolution recovery. The parameters used for reconstruction may vary between vendors, but must permit a good image resolution while maintaining adequate noise levels (using post-processing). Typically, 3 or 5 iterations are necessary and 8 to 10 subsets. Post-processing is usually performed using a Gaussian filter (width at halfmaximum of 4 to 10 mm), or a Butterworth filter (conventional parameters = 10/0.5). Novel reconstruction algorithms, including multimodal reconstruction, are being introduced and can be used alternatively. With a multimodality SPECT/CT co-registered and aligned CT images, SPECT images and SPECT/CT fused images can be generated and visualized. The 3D images are usually displayed as 2D orthogonal (axial, coronal and sagittal) andmaximum intensity projections. SPECT images with and without attenuation correction should be available for review. Care must be taken when judging attenuation corrected images since even a little misalignment between SPECT and CT may cause attenuation and reconstruction artifacts, which can lead to over- or underestimation of the tracer uptake in a certain region. Typical parameters used by the main multimodality camera manufacturers are shown in Table 3. 2

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