Importance of Defect Detectability in Positron Emission Tomography Imaging of Abdominal Lesions.

OBJECTIVES: This study was designed to assess defect detectability in positron emission tomography (PET) imaging of abdominal lesions. METHODS: A National Electrical Manufactures Association International Electrotechnical Commission phantom was used. The simulated abdominal lesion was scanned for 10 min using dynamic list-mode acquisition method. Images, acquired with scan duration of 1-10 min, were reconstructed using VUE point HD and a 4.7 mm full-width at half-maximum (FWHM) Gaussian filter. Iteration-subset combinations of 2-16 and 2-32 were used. Visual and physical analyses were performed using the acquired images. To sequentially evaluate defect detectability in clinical settings, we examined two middle-aged male subjects. One had a liver cyst (approximately 10 mm in diameter) and the other suffered from pancreatic cancer with an inner defect region (approximately 9 mm in diameter). RESULTS: In the phantom study, at least 6 and 3 min acquisition durations were required to visualize 10 and 13 mm defect spheres, respectively. On the other hand, spheres with diameters ≥17 mm could be detected even if the acquisition duration was only 1 min. The visual scores were significantly correlated with background (BG) variability. In clinical settings, the liver cyst could be slightly visualized with an acquisition duration of 6 min, although image quality was suboptimal. For pancreatic cancer, the acquisition duration of 3 min was insufficient to clearly describe the defect region. CONCLUSION: The improvement of BG variability is the most important factor for enhancing lesion detection. Our clinical scan duration (3 min/bed) may not be suitable for the detection of small lesions or accurate tumor delineation since an acquisition duration of at least 6 min is required to visualize 10 mm lesions, regardless of reconstruction parameters. Improvements in defect detectability are important for radiation treatment planning and accurate PET-based diagnosis.

Ventilatory impairment detection based on distribution of respiratory-induced changes in pixel values in dynamic chest radiography: a feasibility study.

PURPOSE: Decreased ventilation is observed on chest radiographs as small changes in X-ray translucency, and ventilatory impairments can therefore be detected by analyzing the distribution of respiratory-induced changes in pixel value. This study was performed to develop a ventilatory impairment detection method based on the distribution of respiratory-induced changes in pixel values. METHODS: Sequential chest radiographs during respiration were obtained using a dynamic flat panel detector system. Respiratory-induced changes in pixel value were measured in each local area and then compared for symmetrical positions in both lungs, which were located at the same distance from the axis of the thorax at the same level. The right-left symmetry was assessed in 20 clinical cases (Abnormal, 14; Normal, 6). RESULTS: In normal controls, the distribution was symmetrical, and there were good correlations of the pixel value changes in both lungs at symmetrical positions (r = 0.66 ± 0.05). In contrast, abnormal cases did not show a symmetrical distribution of pixel value changes (r = 0.40 ± 0.23) due to ventilation abnormalities observed as reductions in pixel value changes. CONCLUSIONS: Ventilatory impairment could be detected as deviation from the right-left symmetry of respiratory-induced changes in pixel value. In particular, the present method could be useful for detecting unilateral abnormalities. However, to detect bilateral abnormalities, further studies are required to develop multilevel detection methods combined with several methods of pattern analysis.

Pulmonary blood flow evaluation using a dynamic flat-panel detector: feasibility study with pulmonary diseases.

PURPOSE: Pulmonary ventilation and circulation dynamics are reflected on fluoroscopic images as changes in X-ray translucency. The purpose of this study was to investigate the feasibility of non-contrast functional imaging using a dynamic flat-panel detector (FPD). METHODS: Dynamic chest radiographs of 20 subjects (abnormal, n = 12; normal, n = 8) were obtained using the FPD system. Image analysis was performed to get qualitative perfusion mapping image; first, focal pixel value was defined. Second, lung area was determined and pulmonary hilar areas were eliminated. Third, one cardiac cycle was determined in each of the cases. Finally, total changes in pixel values during one cardiac cycle were calculated and their distributions were visualized with mapping on the original image. They were compared with the findings of lung perfusion scintigraphy. RESULTS: In all normal controls, the total changes in pixel value in one cardiac cycle decreased from the hilar region to the peripheral region of the lung with left-right symmetric distribution. In contrast, in many abnormal cases, pulmonary blood flow disorder was indicated as a reduction of changes in pixel values on a mapping image. The findings of mapping image coincided with those of lung perfusion scintigraphy. CONCLUSIONS: Dynamic chest radiography using an FPD system with computer analysis is expected to be a new type of functional imaging, which provides pulmonary blood flow distribution additionally.

Changes in regional cerebral blood flow in irradiated regions and normal brain after stereotactic radiosurgery.

OBJECTIVE: To elucidate the radiation effect on the normal brain after stereotactic radiosurgery (SRS), we evaluated the change in regional cerebral blood flow (CBF) in targeted and extra-targeted areas according to the radiation dose given. METHODS: Thirteen patients who underwent SRS for brain tumors or arteriovenous malformations were included in this study. Maximum radiation doses to the lesion ranged from 24 to 37 Gy. Mean and regional CBF were measured by 99mTc-HMPAO scintigraphy with graphic analysis, performed at before, 2 weeks and 3 months (5 patients) after SRS. Under the co-registration with the CT with superimposed isodose distribution, ROIs were set on target (37-20 Gy), peri-target (20-5 Gy) and out-of-field (5-2 Gy and less than 2 Gy) areas on the quantitative SPECT images. RESULTS: Significant reductions in mean CBF (by 7%) and regional CBF in the peri-target areas (by 5-7%) and out-of-field areas (by 6-22%) were recognized at 2 weeks and 3 months after SRS. Regional CBF in the target and peri-target areas did not significantly change, presumably because there was little or no normal tissue in these areas. CONCLUSION: These results suggest that subclinical regional CBF reduction occurs after SRS in the normal brain in out-of-field of radiation.