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In oncological imaging, the sensitivity and specificity of planar bone scans varies depending upon various factors, but generally the sensitivity ranges between 62% - 100% and the specificity between 78%-100%. Most of the times, the degenerative, post traumatic or postoperative changes in cancer patients, make interpretation of planar bone scans difficult or inconclusive. Addition of SPECT (single photon emission computed tomography) and particularly of SPECT-/CT increases the sensitivity and specificity. However, such an approach increases the scanning time dramatically increases and this extra imaging time is often not attainable either due to very sick patients or those who are in pain, or due to logistics or unavailability of camera time for additional study.
Recently a new pharmaceutical sodium fluoride-18 (NaF-18) has come into day-to-day use. This agent is a positron-emitting isotope and was first used in the early 1960s but was not suitable for imaging with rectilinear scanners and gamma cameras. However, with the introduction of Positron Emitting Tomography (PET) scanners in the 1990s, and especially since the widespread introduction of PET/CT scanners, NaF has reemerged as an ideal agent for bone imaging. With the addition of a co-registered low dose CT, the morphology of a lesion can be easily and accurately characterized.
From the patient's perspective a PET bone scan is more easily tolerated than a planar scan. The waiting time after injection to the actually scan is approximately 45 minutes for PET, compared to 3 hours for a conventional bone scan. The actual time taken for a PET bone scan is usually between 15-20 minutes versus 45-60 minutes with a planar scan or even longer if SPECT is performed as an adjunct to the planar scan. Since, a low dose CT scan accompanies the PET bone scan as a routine part of the examination, the patient usually does not need additional imaging such as plain x rays or MRI to differentiate benign from malignant bone processes. Generally, the radiation dose to the patient from a PET bone scan is slightly less than the traditional bone scan, on modern PET scanners.
From a nuclear medicine's perspective, the PET bone scan has a greater sensitivity and specificity than other nuclear medicine techniques. The higher photon flux with NaF-18 compared to traditional bone scanning agents makes the lesions more conspicuous and easier to see. This translates to detection of relatively higher number of lesions on PET bone scan.
From the oncologist's perspective a PET bone scan offers increased sensitivity of 90 percent and increased specificity of 97 percent. The increase is due to the nature of the isotope and scanner (and also the presence of a co-registered low dose CT scan, allowing accurate anatomic characterization of metabolically active lesions.
Singapore PET and Cardiac imaging Centre is the only diagnostic imaging centre in Singapore, performing currently NaF-18 PET bone scan. NaF-18's higher diagnostic accuracy, shorter study times resulting in improved patient convenience and faster reports make it a suitable replacement of the planar bone scan.
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