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Fig. 18 SPECT/CT images of the spine. Sagittal (a), coronal (b), and axial (c) plane fused CT
(grayscale) and SPECT (color over-projection) images from a SPECT/CT study of the spine
obtained for assessment of possible metastatic bone lesions in this patient with a history of
metastatic cancer and back pain (no metastatic lesions are apparent on these images)
taken up by cells undergoing increased glycolytic enzyme activity and increased
glycolysis, seen in pathologic cells such as tumor cells, and results in localized foci
of abnormally increased radiotracer accumulation within the tissues. The radionu-
clide portion of the molecule is
fluorine-18, which emits positrons as part of its
decay process. The emitted positrons then encounter local neighborhood electrons
and undergo annihilation, shortly after being produced. The annihilation of the
electron-positron pair leads to release of two oppositely directed gamma rays,
which are then absorbed and detected in the PET/CT scanner [
16
,
18
]. The two
oppositely directed gamma rays are detected along a coincidence line, resulting in
improved spatial localization data relative to SPECT, and so improved spatial
resolution on the generated images. These coincidence detections are used to
localize the pathologic process.
PET/CT is in widespread use in the detection, staging, and monitoring of cancer,
and has also shown promise in infection imaging. The roles of PET/CT continue to
expand with the development of new targeted radiotracer molecules. Figure
19
shows example images from a patient obtaining a PET/CT scan, extending from the
head to the thighs, without evidence of active spinal metastatic disease. Images
obtained from a whole body (head through thighs) PET/CT scan for a 52 year old
female patient with a history of metastatic lung cancer as shown in Fig.
20
.
fl
8 Ultrasound
Sound waves of frequency range 2
10 MHz are used in clinical medical ultrasound
applications, and are high frequency compared with the spectrum human hearing
ranging 15
-
20 kHz [
1
]. The velocity of sound propagation varies depending on the
-
