Study of OSEM with different subsets in grating-based X-ray differential phase-contrast imaging.

Impressive developments in X-ray imaging are associated with X-ray phase contrast computed tomography based on grating interferometry, a technique that provides increased contrast compared with conventional absorption-based imaging. A new "single-step" method capable of separating phase information from other contributions has been recently proposed. This approach not only simplifies data-acquisition procedures, but, compared with the existing phase step approach, significantly reduces the dose delivered to a sample. However, the image reconstruction procedure is more demanding than for traditional methods and new algorithms have to be developed to take advantage of the "single-step" method. In the work discussed in this paper, a fast iterative image reconstruction method named OSEM (ordered subsets expectation maximization) was applied to experimental data to evaluate its performance and range of applicability. The OSEM algorithm with different subsets was also characterized by comparison of reconstruction image quality and convergence speed. Computer simulations and experimental results confirm the reliability of this new algorithm for phase-contrast computed tomography applications. Compared with the traditional filtered back projection algorithm, in particular in the presence of a noisy acquisition, it furnishes better images at a higher spatial resolution and with lower noise. We emphasize that the method is highly compatible with future X-ray phase contrast imaging clinical applications.

Image quality assessment in digital mammography: part II. NPWE as a validated alternative for contrast detail analysis.

Assessment of image quality for digital x-ray mammography systems used in European screening programs relies mainly on contrast-detail CDMAM phantom scoring and requires the acquisition and analysis of many images in order to reduce variability in threshold detectability. Part II of this study proposes an alternative method based on the detectability index (d') calculated for a non-prewhitened model observer with an eye filter (NPWE). The detectability index was calculated from the normalized noise power spectrum and image contrast, both measured from an image of a 5 cm poly(methyl methacrylate) phantom containing a 0.2 mm thick aluminium square, and the pre-sampling modulation transfer function. This was performed as a function of air kerma at the detector for 11 different digital mammography systems. These calculated d' values were compared against threshold gold thickness (T) results measured with the CDMAM test object and against derived theoretical relationships. A simple relationship was found between T and d', as a function of detector air kerma; a linear relationship was found between d' and contrast-to-noise ratio. The values of threshold thickness used to specify acceptable performance in the European Guidelines for 0.10 and 0.25 mm diameter discs were equivalent to threshold calculated detectability indices of 1.05 and 6.30, respectively. The NPWE method is a validated alternative to CDMAM scoring for use in the image quality specification, quality control and optimization of digital x-ray systems for screening mammography.

Skull base chordomas: presentation of six cases and review of the literature.

Chordomas are uncommon tumours occuring from remnants of the notochord. They are mainly localized in the sacrococcygium, the spine and the skull base. We focused our study on skull base chordomas and reviewed 531 published cases and 6 cases diagnosed in our institution. The six cases diagnosed at our hospital are described with a special mention of a unique case presenting with meningitis. Clinical features, radiology, histopathology and survival with different treatments are reviewed. Skull base chordomas can occur at any age and are slightly more frequent in males. Patients complain most often of diplopia and headaches. Abducens nerve palsy is the commonest neurological finding. Radiological examination should include both CT-scan which shows extensive osteolysis, calcifications and contrast enhancement and MRI for topographical definition. Metastases rarely occur. Treatment remains controversial but combined surgery and radiotherapy is the best treatment with a 5 year survival rate of 75%.

Clinical and radiological findings in Pallister-Killian syndrome.

Pallister-Killian syndrome (PKS) is a potentially lethal disorder with facial dysmorphism, pigmentary skin anomalies, developmental delay and major visceral anomalies, such as diaphragmatic hernia, anorectal malformation, and congenital heart disease. PKS is causally associated with mosaic tetrasomy of chromosome 12p. A routine chromosome analysis in peripheral lymphocytes usually fails to detect the mosaic state. A prompt diagnosis rests on clinical awareness and a subsequent chromosome or molecular analysis in fibroblasts, buccal mucosal cells, or bone marrow cells. We report here on three infants with PKS. One infant had aortic dilatation, a previously unreported association in PKS. More importantly, all infants showed a recognizable, though mild, pattern of skeletal changes mainly affecting axial bones, including delayed ossification of the vertebral bodies and pubic bones, flared anterior ribs, and broad metaphyses of the long bones, particularly of the femora. These skeletal changes should be considered as a useful diagnostic sign in PKS. Awareness of the axial skeletal alterations can be helpful in prompting clinicians to search for mosaic tetrasomy 12p and perform chromosomal analysis in appropriate tissue types.

Surgical interventions with fatal outcome: Utility of multi-phase postmortem CT angiography

Cases of fatal outcome after surgical intervention are autopsied to determine the cause of death and to investigate whether medical error caused or contributed to the death. For medico-legal purposes, it is imperative that autopsy findings are documented clearly. Modern imaging techniques such as multi-detector computed tomography (MDCT) and postmortem CT angiography, which is used for vascular system imaging, are useful tools for determining cause of death. The aim of this study was to determine the utility of postmortem CT angiography for the medico-legal death investigation. This study investigated 10 medico-legal cases with a fatal outcome after surgical intervention using multi-phase postmortem whole body CT angiography. A native CT scan was performed as well as three angiographic phases (arterial, venous, and dynamic) using a Virtangio((R)) perfusion device and the oily contrast agent, Angiofil((R)). The results of conventional autopsy were compared to those from the radiological investigations. We also investigated whether the radiological findings affected the final interpretation of cause-of-death. Causes of death were hemorrhagic shock, intracerebral hemorrhage, septic shock, and a combination of hemorrhage and blood aspiration. The diagnoses were made by conventional autopsy as well as by postmortem CT angiography. Hemorrhage played an important role in eight of ten cases. The radiological exam revealed the exact source of bleeding in seven of the eight cases, whereas conventional autopsy localized the source of bleeding only generally in five of the seven cases. In one case, neither conventional autopsy nor CT angiography identified the source of hemorrhage. We conclude that postmortem CT angiography is extremely useful for investigating deaths following surgical interventions. This technique helps document autopsy findings and allows a second examination if it is needed; specifically, it detects and visualizes the sources of hemorrhages in detail, which is often of particular interest in such cases.

Delayed contrast-enhanced MRI of the coronary artery wall in takayasu arteritis.

BACKGROUND: Takayasu arteritis (TA) is a rare form of chronic inflammatory granulomatous arteritis of the aorta and its major branches. Late gadolinium enhancement (LGE) with magnetic resonance imaging (MRI) has demonstrated its value for the detection of vessel wall alterations in TA. The aim of this study was to assess LGE of the coronary artery wall in patients with TA compared to patients with stable CAD. METHODS: We enrolled 9 patients (8 female, average age 46±13 years) with proven TA. In the CAD group 9 patients participated (8 male, average age 65±10 years). Studies were performed on a commercial 3T whole-body MR imaging system (Achieva; Philips, Best, The Netherlands) using a 3D inversion prepared navigator gated spoiled gradient-echo sequence, which was repeated 34-45 minutes after low-dose gadolinium administration. RESULTS: No coronary vessel wall enhancement was observed prior to contrast in either group. Post contrast, coronary LGE on IR scans was detected in 28 of 50 segments (56%) seen on T2-Prep scans in TA and in 25 of 57 segments (44%) in CAD patients. LGE quantitative assessment of coronary artery vessel wall CNR post contrast revealed no significant differences between the two groups (CNR in TA: 6.0±2.4 and 7.3±2.5 in CAD; p = 0.474). CONCLUSION: Our findings suggest that LGE of the coronary artery wall seems to be common in patients with TA and similarly pronounced as in CAD patients. The observed coronary LGE seems to be rather unspecific, and differentiation between coronary vessel wall fibrosis and inflammation still remains unclear.

Investigation of discrete imaging models and iterative image reconstruction in differential X-ray phase-contrast tomography.

Differential X-ray phase-contrast tomography (DPCT) refers to a class of promising methods for reconstructing the X-ray refractive index distribution of materials that present weak X-ray absorption contrast. The tomographic projection data in DPCT, from which an estimate of the refractive index distribution is reconstructed, correspond to one-dimensional (1D) derivatives of the two-dimensional (2D) Radon transform of the refractive index distribution. There is an important need for the development of iterative image reconstruction methods for DPCT that can yield useful images from few-view projection data, thereby mitigating the long data-acquisition times and large radiation doses associated with use of analytic reconstruction methods. In this work, we analyze the numerical and statistical properties of two classes of discrete imaging models that form the basis for iterative image reconstruction in DPCT. We also investigate the use of one of the models with a modern image reconstruction algorithm for performing few-view image reconstruction of a tissue specimen.

How to operate a university institute as a radiological emergency service?

The Institute of Radiation Physics (IRA) is attached to the Department of Medical Radiology at the Vaud University Hospital Center (CHUV) in Lausanne. The Institute's main tasks are strongly linked to the medical activities of the Department: radiotherapy, radiodiagnostics, interventional radiology and nuclear medicine. The Institute also works in the fields of operational radiation protection, radiation metrology and radioecology. In the case of an accident involving radioactive materials, the emergency services are able to call on the assistance of radiation protection specialists. In order to avoid having to create and maintain a specific structure, both burdensome and rarely needed, Switzerland decided to unite all existing emergency services for such events. Thus, the IRA was invited to participate in this network. The challenge is therefore to integrate a university structure, used to academic collaborations and the scientific approach, to an interventional organization accustomed to strict policies, a military-style command structure and "drilled" procedures. The IRA's solution entails mobilizing existing resources and the expertise developed through professional experience. The main asset of this solution is that it involves the participation of committed collaborators who remain in a familiar environment, and are able to use proven materials and mastered procedures, even if the atmosphere of an accident situation differs greatly from regular laboratory routines. However, this solution requires both a commitment to education and training in emergency situations, and a commitment in terms of discipline by each collaborator in order to be integrated into a response plan supervised by an operational command center.