Evaluation of a rigid registration method of lung perfusion SPECT and thoracic CT.

ABSTRACT

OBJECTIVE: The objective of our study was to evaluate a rigid registration method in lung perfusion SPECT using thoracic CT as a standard. MATERIALS AND METHODS: The reproducibility of markers selection and the robustness of the method were assessed on a torso phantom. The accuracy of registration regarding the number and location of markers and the breathing state during CT was evaluated on eight patients using 10 external markers placed around the thorax before SPECT and CT acquisitions. The accuracy of registration was assessed using the mean errors (ME) between 10 markers after registration. RESULTS: Registration using external markers on a phantom was accurate (ME, < 3 mm) when rotation was less than 40 degrees (p = 0.02). The accuracy of registration improved markedly from four to six markers for phantom (5.5-3.6 mm) and patients (11.2-9.5 mm) and then remained constant up to 10 markers. The ME was less when using markers that well encompassed the thorax for phantom and patients (p = 0.02 and p = 0.05, respectively). The use of four anatomic markers was not accurate (ME, 20 mm). CONCLUSION: The registration method is reproducible and accurate, and six external markers were required to get an ME of less than 10 mm in patients.