Nuclear Cardiology: Nuclear Cardiology:

100 Nuclear Cardiology, The Basicsrate during SPECT image acquisition was irregular, not all 8 or 16bins of an ECG-gated SPECT study have accumulated the same numberof counts per stop, resulting in darker and lighter images. However,one should be aware that ECG-gating irregularities are oftensubtle and may not be spotted directly from planar projection images.Localized noncardiac radiotracer uptakeDepending on the size of the FOV, rotating projection images alsodisplay part of the chest and upper abdomen. When inspecting rotatingimages, one should pay attention to normal and abnormalextracardiac radiotracer accumulation. One may see varying degreesof uptake in the salivary glands, thyroid gland and stomach mucosa.This is not abnormal and is due to the presence of free unlabeledTc-99m pertechnetate. At times the skeleton may be faintly visualized;the significance of the latter is unclear. However, localizedradiotracer accumulation in the mediastinum, breast(s), and axillashould be considered abnormal and may indicate malignancy. Suchabnormal extracardiac uptake should be mentioned in the final reportto the referring physician and further clinical work-up should besuggested.Increased lung uptakeIncreased radiotracer lung uptake, in particular when present onstress images and not on rest images, is a sign of transient leftventricular dysfunction during stress. Lung uptake is quantified aslung/heart ratio. The lower limit of normal lung/heart ratio is 0.50 forTl-201 and 0.42 for Tc-99m-Sestamibi or Tetrofosmin.Reconstructed SlicesThe display of reconstructed SPECT slices has been standardized(1–3) (Fig. 10-2). Three sets of tomographic slices are reconstructed:short axis slices, horizontal long axis slices, and vertical long axis slices.The stress (A) and rest or delayed (B) images are displayed in two rowsof images (stress on top and rest below) to facilitate comparison (Fig. 10-3).The short-axis images are displayed from apex (left) to base (right). Thevertical long-axis slices from septum (left) to lateral wall (right). Thehorizontal long-axis are displayed from inferior wall (left) to anteriorwall (right).Images are preferably displayed on computer screen in color or “whiteon black” using a linear gray scale. It is important that the display ofimages is standardized and not changed randomly. Certain color scaleshave a tendency to exaggerate subtle differences in myocardialradiotracer uptake, other color scales may have the opposite effect.