全身照射的前期准备及在造血干细胞移植预处理中的应用

目的 探讨医用直线加速器高能X线全身照射(TBI)在造血干细胞移植预处理中的应用及治疗前的必要准备。方法 利用仿真人体体模和热释光测量设备，在高能X线全身照射条件下，对远距离大照射野的射线剂量均匀性进行测量和调整并测量了人体各重要组织和器官的吸收剂量。对已完成的12例TBI病例进行初步分析，观察临床应用效果。结果 经调整后的大照射野完全符合治疗要求，获得了人体内在全身照射条件下各器官的实际吸收剂量，为全身照射时照射剂量的评估和监测提供了可靠数据。完成的12例TBI治疗均成功。结论 经过仔细测量和调整后的医用直线加速器，完全可以胜任造血干细胞预处理全身照射的各项要求，临床应用可靠。     

Evaluation of accuracy in MS lesion volumetry using realistic lesion phantoms

RATIONALE AND OBJECTIVES: Quantitative analysis of such small structures as focal lesions in patients with multiple sclerosis (MS) is an important issue in both diagnosis and therapy monitoring. To reach clinical relevance, the reproducibility and accuracy of a proposed method have to be validated. We propose a framework for the generation of realistic digital phantoms of MS lesions of known volumes and their incorporation into a magnetic resonance (MR) data set of a healthy volunteer. MATERIALS AND METHODS: We generated 54 data sets from a multispectral brain scan of a healthy volunteer with incorporated MS lesion phantoms. Lesion phantoms were created using different shapes (three), sizes (six), and orientations (three). An evaluation is carried out from a manual analysis of three human experts and two different semiautomatic approaches, with and without explicit modeling of partial volume effects (PVEs). RESULTS: Intraobserver and interobserver studies were performed for the phantom data sets. All experts overestimated the true lesion volume for any phantom data set (median overestimation between 42.9% and 63.2%). Relative error and variability increased with decreasing lesion size. Similar results were obtained for the semiautomatic approach without PVE modeling. Only the approach with explicit PVE modeling was capable of generating accurate volumetric results with low systematic error. CONCLUSION: The proposed framework based on realistic lesion phantoms incorporated into an MR scan allows for quantitative assessment of the accuracy of manual and automated lesion volumetry. Results clearly show the importance of an improved gold standard in lesion volumetry beyond voxel counting.     

Accuracy of cardiac PET imaging using post-injection transmission scan

The purpose of this study was to investigate the accuracy of cardiac PET with post-injection transmission scans. METHODS: We performed a phantom study using 18F solution as well as 13N-ammonia PET study of ten patients. The average activities of no myocardial defect phantom model were estimated, and myocardial defect sizes of 12 phantom models were measured by pre- and post-injection transmission methods at various 18F activities. In 13N-ammonia PET at rest and during adenosine triphosphate (ATP) stress studies, measured defect sizes were compared between both methods. RESULTS: The ratios of average activity estimated by both methods (post/pre value) were almost 1.00 at each 18F activity and segment. Measured defect sizes by both methods showed an excellent correlation with true defect sizes (r = 0.98, p < 0.01 for pre vs. true value: r = 0.98, p < 0.01 for post vs. true value). The mean absolute errors of measurements were minimal up to 3.5% LV, and were similar between both methods. In 13N-ammonia PET, measured defect sizes by both methods also showed a good correlation (r = 0.97, p < 0.01). CONCLUSION: The results indicate that cardiac PET imaging with post-injection transmission scan provides information on myocardial tracer activity as well as myocardial defect size as does conventional pre-injection transmission method.     

A realistic 3-D gated cardiac phantom for quality control of gated myocardial perfusion SPET: the Amsterdam gated (AGATE) cardiac phantom

A realistic 3-D gated cardiac phantom with known left ventricular (LV) volumes and ejection fractions (EFs) was produced to evaluate quantitative measurements obtained from gated myocardial single-photon emission tomography (SPET). The 3-D gated cardiac phantom was designed and constructed to fit into the Data Spectrum anthropomorphic torso phantom. Flexible silicone membranes form the inner and outer walls of the simulated left ventricle. Simulated LV volumes can be varied within the range 45–200 ml. The LV volume curve has a smooth and realistic clinical shape that is produced by a specially shaped cam connected to a piston. A fixed 70-ml stroke volume is applied for EF measurements. An ECG signal is produced at maximum LV filling by a controller unit connected to the pump. This gated cardiac phantom will be referred to as the Amsterdam 3-D gated cardiac phantom, or, in short, the AGATE cardiac phantom. SPET data were acquired with a triple-head SPET system. Data were reconstructed using filtered back-projection following pre-filtering and further processed with the Quantitative Gated SPECT (QGS) software to determine LV volume and EF values. Ungated studies were performed to measure LV volumes ranging from 45 ml to 200 ml. The QGS-determined LV volumes were systematically underestimated. For different LV combinations, the stroke volumes measured were consistent at 60–61 ml for 8-frame studies and 63–65 ml for 16-frame studies. QGS-determined EF values were slightly overestimated between 1.25% EF units for 8-frame studies and 3.25% EF units for 16-frame studies. In conclusion, the AGATE cardiac phantom offers possibilities for quality control, testing and validation of the whole gated cardiac SPET sequence, and testing of different acquisition and processing parameters and software.An erratum to this article can be found at     

Assessment of calcium scoring performance in cardiac computed tomography

Electron beam tomography (EBT) has been used for cardiac diagnosis and the quantitative assessment of coronary calcium since the late 1980s. The introduction of mechanical multi-slice spiral CT (MSCT) scanners with shorter rotation times opened new possibilities of cardiac imaging with conventional CT scanners. The purpose of this work was to qualitatively and quantitatively evaluate the performance for EBT and MSCT for the task of coronary artery calcium imaging as a function of acquisition protocol, heart rate, spiral reconstruction algorithm (where applicable) and calcium scoring method. A cardiac CT semi-anthropomorphic phantom was designed and manufactured for the investigation of all relevant image quality parameters in cardiac CT. This phantom includes various test objects, some of which can be moved within the anthropomorphic phantom in a manner that mimics realistic heart motion. These tools were used to qualitatively and quantitatively demonstrate the accuracy of coronary calcium imaging using typical protocols for an electron beam (Evolution C-150XP, Imatron, South San Francisco, Calif.) and a 0.5-s four-slice spiral CT scanner (Sensation 4, Siemens, Erlangen, Germany). A special focus was put on the method of quantifying coronary calcium, and three scoring systems were evaluated (Agatston, volume, and mass scoring). Good reproducibility in coronary calcium scoring is always the result of a combination of high temporal and spatial resolution; consequently, thin-slice protocols in combination with retrospective gating on MSCT scanners yielded the best results. The Agatston score was found to be the least reproducible scoring method. The hydroxyapatite mass, being better reproducible and comparable on different scanners and being a physical quantitative measure, appears to be the method of choice for future clinical studies. The hydroxyapatite mass is highly correlated to the Agatston score. The introduced phantoms can be used to quantitatively assess the performance characteristics of, for example, different scanners, reconstruction algorithms, and quantification methods in cardiac CT. This is especially important for quantitative tasks, such as the determination of the amount of calcium in the coronary arteries, to achieve high and constant quality in this field. Electronic Publication     

Investigation of ultrasound image processing to improve perceptibility of microcalcifications

Purpose  This article describes an investigation of the detectability of breast microcalcifications by ultrasound imaging. Methods  Two kinds of experiments were performed to evaluate the spatial and contrast resolution of microstructures in an agar graphite phantom and to analyze human perception of tiny spots. Results  The results showed that most of the difficulties in finding microstructures were not only due to lower echo levels but also to obstructions in the surrounding texture of the image. Based on these results, a new image processing method was proposed to emphasize microcalcifications in mammary glands. This method utilized statistical analysis of the echo signals and also considered the structural pattern of the mammary gland. Processed images from some clinical cases showed adequate extraction of the microcalcifications with efficient cancellation of the mammary gland structure. Conclusion  The results suggested that the perception of microcalcifications could be improved by the proposed method.     

应用Geant4计算光子外照射对人体产生的有效剂量

在Geant4中构建ORNL程式化混合模体,应用此模体计算不同能量下平行光子入射的人体有效剂量。计算结果以吸收剂量与空气比释动能比值的形式呈现。计算结果与ICRP74值进行了对比验证。     

Phantom testis syndrome: prevalence, phenomenology and putative mechanisms

Chronic phantom pain has been found in up to 78% of limb amputees and is a major complication of limb amputation. Less is known about phantom phenomena after the amputation of other, i.e. visceral, parts of the body. In a retrospective design, we identified 539 patients in whom one testis was removed between 1995 and 2005. The operative technique was a unilateral standard radical inguinal orchiectomy. The underlying pathology in all cases was a testicular germ cell tumour. All patients received a detailed questionnaire asking about the occurrence of phantom testis pain (pain felt in the removed testis), phantom testis sensations (non-painful sensations as if the removed testis was still intact) and hallucinations (illusionary perceptions on the removed testis). Furthermore, we asked about the occurrence and clinical presentation of pain before and after surgery and about pre-operative testicular pain. Out of 238 respondents, 125 patients (53%) reported any kind of phantom experience. The prevalence of phantom testis pain was 25% (60/238), non-painful phantom sensations 16% (37/238) and male gonad hallucinations 12% (28/238). Patients with phantom symptoms reported pre-operative pain in the removed testis more often than patients without phantom symptoms. This study presents first data on the clinical characteristics and possible mechanisms of the phantom testis syndrome after surgical removal of one testis.