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Attenuation Correction of PET Images with Respiration-Averaged CT Images in PET/CT

¹ Department of Imaging Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas
² Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York
³ Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas
⁴ Department of Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas
⁵ Department of Nuclear Medicine, The University of Texas M.D. Anderson Cancer Center, Houston, Texas

View larger version (65K): [in a new window]   FIGURE 1. Formation of ACT data for PET AC. HCT data are in first panel (left). Some HCT data not overlapping ACT data (third panel) are repeated in second panel. We combined HCT data from second panel and ACT data from third panel to make ACT + HCT data in fourth panel. The main purpose of this fusion was to make ACT + HCT data the same format as HCT for PET AC. All images are coronal. These images were from patient 5 (also shown in Fig. 5).

View larger version (9K): [in a new window]   FIGURE 2. Frequency and magnitude of misalignment between PET and HCT of lower right thorax in 100 consecutive PET/CT studies.

View larger version (40K): [in a new window]   FIGURE 3. Respiratory signal recorded during HCT before PET. Recording was made with strain gauge monitoring respiratory motion around waist at sampling frequency of 1 kHz. Scout scan was taken to survey anatomy; during this scan, patient was breathing freely (FB). After scout scan was taken, patient was instructed to prepare for limited breath-hold (BH) at midexpiration for HCT. It was noted that patient held breath at state different from any breathing state before breath-hold.

View larger version (59K): [in a new window]   FIGURE 4. (A) Axial HCT and PET data (corrected by HCT) for tumor 1 (patient 1). (B) Corresponding axial ACT and PET data (corrected by ACT). SUV for HCT PET and ACT PET were 2.3 and 3.6, respectively. SUV increased 59.0% from HCT PET to ACT PET. (C) Coronal HCT, HCT PET, and maximum-intensity projection (MIP) of HCT PET data. (D) Coronal ACT, ACT PET, and MIP of ACT PET data. With ACT, there was a significant reduction in breathing artifacts caused by different breathing states during HCT and PET, suggesting that ACT can effectively reduce breathing artifacts and improve quantification of PET data. On each image, crosshair or arrow indicates tumor location. Same tumor can be seen in both ACT and PET data in B but not clear in PET data and not in HCT data in A.

View larger version (79K): [in a new window]   FIGURE 5. (A) Axial HCT and PET data (corrected by HCT) for tumor 10 (patient 5). (B) Corresponding axial ACT and PET data (corrected by ACT). To augment interpretation, both HCT and ACT images are shown with CT level of –700 and window width of 1,000. SUV for HCT PET and ACT PET were 4.3 and 7.4, respectively. SUV increased 70.1% from HCT PET to ACT PET. (C) Coronal HCT, HCT PET, and maximum-intensity projection (MIP) of HCT PET data. (D) Coronal ACT, ACT PET, and MIP of ACT PET data. With ACT, there was a significant reduction in breathing artifacts caused by different breathing states during HCT and PET. Note that ACT did not cover whole lung and was still able to correct for breathing artifacts. On each image, crosshair or arrow indicates tumor location.

View larger version (62K): [in a new window]   FIGURE 6. (A) Axial HCT and PET data (corrected by HCT) for tumor 11 (patient 6). (B) Corresponding ACT and PET data (corrected by ACT). SUV for HCT PET and ACT PET were 1.9 and 3.8, respectively. SUV increased 97.4% from HCT PET to ACT PET. (C) Coronal HCT, HCT PET, and maximum-intensity projection (MIP) of HCT PET data. (D) Coronal ACT, ACT PET, and MIP of ACT PET data. With ACT, there was a significant reduction in breathing artifacts caused by different breathing states during HCT and PET. On each image, crosshair or arrow indicates tumor location.