Thesis

43 The EANM practice guideline for Bone Scintigraphy the FOV of the gamma-camera. The larger the FOV, the larger the number of total counts required to give similar count densities over equivalent regions of the skeleton [51]. Moreover, the presence of organs (typically the kidneys) with physiologically high count densities may hamper visualization of contiguous structures (typically the spine). A pinhole collimator can be used to complete the examination by acquiring high resolution planar views of a small area, particularly in infants and children. A total count of 50,000 to 100,000 is recommended. Zoom magnification or a converging collimator may also be used to improve resolution. The physician interpreting the image should be notified when collimators that introduce distortions, such as a pinhole, are used. Additional projections, such as lateral, oblique, tangential and special views may be obtained if necessary. Whole-body bone scintigraphy can be accomplished withmultiple overlapping (spot) images or with continuous imaging (i.e. whole-body scan) obtained in both anterior and posterior projections. In adults, whole-body studies are currently preferred. In children it is common to perform multiple planar acquisitions, rather than wholebody images. When spot views are used as the primary method of acquisition, the regions of skeleton covered by each spot viewmust overlap, to avoidmissing any area. The acquisition of whole-body images is routinely performed. Exceptions may include localized symptoms or patient specific factors (children, patients with severe pain, claustrophobic patients). The recommended scanning speed is 25 to 30 cm per minute for early phase images (if applicable) and 10 to 15 cm per minute for delayed acquisitions. The scanning speed should be adjusted so that routine anterior and posterior whole-body images contain each more than 1.5 million counts. The image format is 1024x256 or 2048x512. The whole-body images can be processed with a spatial filter to improve pixel to pixel variation. It is often helpful to increase the time period between tracer injection and image acquisition, in order to optimize the bone to background ratio, in case of poor visualization of the skeleton (e.g. renal insufficiency), for specific anatomical regions (e.g. the pelvis in case of urinary retention, or distal extremities in case of peripheral circulatory disorders), or in older patients with impaired bone metabolism (osteoporosis, osteomalacia). Usually, the goal of these late (6-24 hour) images is to detect stress fractures, osteitis, osteomyelitis, or bone metastases. 3. SPECT and SPECT-CT acquisitions Diagnostic sensitivity and specificity of bone scanning can be significantly increased by using SPECT or, if available, SPECT/CT. Tomographic images may thus be acquired 2

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