Sentinel node detection in patients with breast cancer: low-energy all-purpose collimator or medium-energy collimator?
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Adult↗
Biomedical subjects
Karin Knesaurek
Publications and source records attributed to Karin Knesaurek.
Improving 3D PET imaging by restoration: a phantom study.
The main objective of our work is to improve 3D PET imaging. Compared with 2D PET, 3D PET imaging has slightly worse axial resolution and a significantly higher contribution of scatter and randoms, but 3D PET has much better sensitivity than 2D PET imaging. A Jaszczak deluxe phantom was acquired in 3D mode on our GE Advance PET system. Activity of 333 MBq of 18F was uniformly distributed. Prior to the emission scan, blank and transmission scans had been acquired. They were used for attenuation correction. The duration of the emission scan was 20 min, transmission 10 min, and blank 20 min. Standard FBP reconstruction software provided by the vendor was used to obtain slice images. Point spread function was also acquired in a 21 cm diameter cylinder phantom filled with water 6.0 cm from the center and used to create restoration filters. Two restoration filters were applied, medium and sharp. Results showed significant improvement in resolution, contrast and detectability of the cold rods. The artifacts outside the phantom were also significantly reduced. For 11.1 mm rods, average contrast was 0.49+/-0.02 in the original image, 0.52+/-0.04 in the medium restored image, and in the sharply restored image 0.75+/-0.05. For 7.9 mm rods, average contrast was 0.07+/-0.01 in the original image, 0.21+/-0.03 in the medium restored image, and 0.50+/-0.04 in the sharply restored image. The amount of noise in the uniform slices, measured as the coefficient of variation (COV), was 5.5, 7.1 and 10.8% in the original image and in the images restored with medium and sharp filters, respectively. In conclusion, restoration can significantly improve the resolution and contrast of 3D PET imaging.
Phantoms, Imaging↗
Reducing exposure from 57Co sources during breast lymphoscintigraphy by optimizing energy windows and other suggested enhancements of acquisition and the display of images.
UNLABELLED: We set out to measure the reduction in exposure attained by using a weak 57Co sheet source with optimal energy windows. METHODS: Two groups of 10 lymphoscintigraphy studies were analyzed. Group 1 consisted of 10 studies obtained with a stronger source of 57Co, 59 MBq (1.6 mCi) at the time of data acquisition, with transmission images acquired at 3 energy windows of 115-129, 130-134, and 135-150 keV. Group 2 consisted of 10 studies with a weaker sheet source of 57Co, 11 MBq (0.3 mCi). Transmission images were acquired at 3 energy windows of 112-132, 130-134, and 135-150 keV. Same-sized regions of interest (ROIs) were drawn on the patient's torso (PT) and on the nonattenuated image of the transmission source itself (TS), all 1-min images. The counts in each ROI obtained over 1 min and the ratios between the TS ROI and the PT ROI were calculated for all of the energies. Dosimetry calculations based on measured exposure rates and the activity of the sheet sources were used to calculate the patient equivalent dose at 30 cm. RESULTS: For the 57Co energy window, group 1 had an average ROI count of 1,955 in the TS region and 135 counts in the PT region. The average ratio of TS/PT was 15.4. Similarly, group 2 had an average ROI count of 646.4 in the TS region and 91.2 counts in the PT region. The average ratio of TS/PT was 8.6. The relative "outlining performance," when comparing the 57Co and 99mTc windows, showed an average improvement when using the 57Co window of 4.4 and 5.8 times for group 1 and group 2, respectively (TS/PT at 57Co window)/(TS/PT at 99mTc window). Estimates of the patient equivalent dose per study were 2.30 microSv for the stronger 57Co flood source and 0.46 microSv for the weaker 57Co flood source, a 5-fold reduction in equivalent dose. Technologists received less than half of the above doses. CONCLUSION: Use of expanded, separate energy windows optimized for the primary 122-keV photon of 57Co greatly improves transmission scan image quality compared with the standard 140-keV 99mTc windows used for the delineation of the sentinel node. This markedly reduces exposure for all, by allowing the use of a weaker source, and can save time.
Breast↗
Comparison of 2-dimensional and 3-dimensional 82Rb myocardial perfusion PET imaging.
UNLABELLED: We compared 2-dimensional (2D) and 3-dimensional (3D) (82)Rb PET imaging in 3 different experiments: in a realistic heart-thorax phantom, in a uniformity-resolution phantom, and in 14 healthy volunteers. METHODS: A nonuniform heart-thorax phantom was filled with 111 MBq of (82)Rb injected into the left ventricular (LV) wall. In the LV wall of the cardiac phantom, 3 inserts-1, 2, and 3 cm in diameter-were placed to simulate infarcts. A standard rest cardiac PET imaging protocol in 2D and 3D modes was used. Following the same protocol, a uniformity-resolution phantom with uniformly distributed activity of 1,998 MBq and 740 MBq of (82)Rb in water was used to obtain 2D PET images and 3D PET images, respectively. All 2D volunteer studies were performed by injecting 2,220 MBq of (82)Rb intravenously. For half the volunteers, 3D studies were performed with a high dose (HD) (2,220 MBq) of (82)Rb; for the remainder of the 3D studies, a low dose (LD) (740 MBq) of (82)Rb was used. In the 2D and LD 3D studies, there was a delay of 2 min and 3 min, respectively, followed by a 6-min acquisition. In the HD 3D volunteer studies, there was a delay of 5 min followed by a 6-min acquisition. Circumferential profiles of the short-axis slices and the contrast of the inserts were used to evaluate the cardiac phantom PET images. The transaxial slices from the uniformity-resolution phantom were evaluated by visual inspection and by measuring uniformity. The human studies were evaluated by measuring the contrast between LV wall and LV cavity, using linear profiles and visual analysis. RESULTS: In the cardiac phantom study, circumferential profiles for the 2D and 3D images were similar. The contrast values for the 1-, 2-, and 3-cm inserts in the 2D study were 0.19 +/- 0.03, 0.34 +/- 0.05, and 0.61 +/- 0.03, respectively. The respective contrast values in the 3D study were 0.15 +/- 0.02, 0.36 +/- 0.04, and 0.52 +/- 0.05. In the uniformity-resolution phantom study, the coefficients of variation, calculated for a representative uniform slice, were 5.3% and 7.6% for the 2D and 3D studies, respectively. For the 7 volunteers on whom HD 3D was used, the mean 2D contrast was 0.33 +/- 0.08 and the mean HD 3D contrast was 0.35 +/- 0.08 (P = not statistically significant). For the other 7 volunteers, on whom LD 3D was used, the mean 2D contrast was 0.39 +/- 0.06 and the mean LD 3D contrast was 0.39 +/- 0.10 (P = not statistically significant). In the tomographic slices, the 2D and 3D images and polar plots were similar. CONCLUSION: When obtained with a PET system having a high counting-rate performance, 2D and 3D (82)Rb PET cardiac images are comparable. LD 3D imaging can make (82)Rb PET cardiac imaging more affordable.
Heart↗