Influence of Attenuation Correction by Brain Perfusion SPECT/CT Using a Simulated Abnormal Bone Structure: Comparison Between Chang and CT Methods.

Brain perfusion SPECT has physical phenomena such as attenuation, scatter, and degradation of resolution that impair accuracy on data acquisition. Chang and CT methods have spread application for attenuation correction (AC) and indicate the utility of AC using a brain phantom without a bone or with a normal bone structure. However, nonuniform AC of an abnormal bone structure such as postoperative bone defect after burr-hole surgery has not yet been evaluated. Therefore, we evaluated the influence of nonuniform AC of an abnormal bone structure between the 2 AC methods. Methods: We created 5 brain phantoms simulating an abnormal bone structure such as frontal, occipital, and right temporal bone defects as well as with and without a bone, which compared the influence among 3-dimensional ordered-subset expectation maximization (OSEM) incorporating scatter, attenuation, and resolution recovery corrections, and obtained 3 reconstruction processing images: OSEM (non-AC; NAC), OSEM (Chang), and OSEM (CTAC). The average counts of the 5 brain phantoms by OSEM (NAC), OSEM (Chang), and OSEM (CTAC) were evaluated by a count profile curve and counts ratio in the region of interest. Results: The counts of OSEM (NAC) and OSEM (Chang) with a bone were approximately 7% higher than those without a bone, whereas OSEM (CTAC) had a similar count ratio. The count ratio of frontal or occipital lobes with a bone defect on both OSEM (NAC) and OSEM (Chang) was 5%-10% higher than that in frontal or occipital lobes without a bone defect; however, OSEM (CTAC) had nearly identical frontal or occipital lobes with and without a bone defect. Conclusion: We conducted a phantom study simulated with and without a bone defect to demonstrate the influence of brain counts between 2 different AC methods. Although the Chang method did not correct the influence of the bone defect due to the use of a uniform attenuation coefficient, the CTAC method correctly conducted AC regardless of the presence of a bone defect.