Rib fractures at postmortem computed tomography (PMCT) validated against the autopsy

To evaluate the sensitivity of postmortem computed tomography (PMCT) in rib fracture detection validated against autopsy. Fifty-one forensic cases underwent a postmortem CT prior to forensic autopsy. Two image readers (radiologist and forensic pathologist) assessed high resolution CT data sets for rib fractures. Correct recognition rates (CRR), sensitivity and specificity values were calculated over all observations as well as individually for every rib and region. Additionally, for partial rib fractures the sensitivity of autopsy was calculated vice versa. 3876 entries in each study protocol (autopsy, PMCT radiologist and PMCT forensic pathologist) were investigated. A total of 690 fractures (autopsy), 491 (PMCT and radiologist) and 559 (PMCT and forensic pathologist) were detected. The CRR was 0.85. Sensitivity and specificity of PMCT for rib fracture detection were 0.63 (0.58 radiologist, 0.68 forensic pathologist) and 0.97 (both readers 0.97), respectively. Low CRR and sensitivity values were obtained for antero-lateral fractures. Partial rib fractures were better detected by PMCT. PMCT has a rather low sensitivity for rib fracture detection when validated against autopsy and indicates that clinical CT may also demonstrate a reasonable number of false negatives. Partial rib fractures often remain undetected at autopsy.

A realistic Computed Tomography simulator for small motion analysis of cerebral aneurysms.

This paper describes a realistic simulator for the Computed Tomography (CT) scan process for motion analysis. In fact, we are currently developing a new framework to find small motion from the CT scan. In order to prove the fidelity of this framework, or potentially any other algorithm, we present in this paper a simulator to simulate the whole CT acquisition process with a priori known parameters. In other words, it is a digital phantom for the motion analysis that can be used to compare the results of any related algorithm with the ground-truth realistic analytical model. Such a simulator can be used by the community to test different algorithms in the biomedical imaging domain. The most important features of this simulator are its different considerations to simulate the best the real acquisition process and its generality.

Update on the non-prewhitening model observer in computed tomography for the assessment of the adaptive statistical and model-based iterative reconstruction algorithms.

The state of the art to describe image quality in medical imaging is to assess the performance of an observer conducting a task of clinical interest. This can be done by using a model observer leading to a figure of merit such as the signal-to-noise ratio (SNR). Using the non-prewhitening (NPW) model observer, we objectively characterised the evolution of its figure of merit in various acquisition conditions. The NPW model observer usually requires the use of the modulation transfer function (MTF) as well as noise power spectra. However, although the computation of the MTF poses no problem when dealing with the traditional filtered back-projection (FBP) algorithm, this is not the case when using iterative reconstruction (IR) algorithms, such as adaptive statistical iterative reconstruction (ASIR) or model-based iterative reconstruction (MBIR). Given that the target transfer function (TTF) had already shown it could accurately express the system resolution even with non-linear algorithms, we decided to tune the NPW model observer, replacing the standard MTF by the TTF. It was estimated using a custom-made phantom containing cylindrical inserts surrounded by water. The contrast differences between the inserts and water were plotted for each acquisition condition. Then, mathematical transformations were performed leading to the TTF. As expected, the first results showed a dependency of the image contrast and noise levels on the TTF for both ASIR and MBIR. Moreover, FBP also proved to be dependent of the contrast and noise when using the lung kernel. Those results were then introduced in the NPW model observer. We observed an enhancement of SNR every time we switched from FBP to ASIR to MBIR. IR algorithms greatly improve image quality, especially in low-dose conditions. Based on our results, the use of MBIR could lead to further dose reduction in several clinical applications.

Computed tomography commissioning programmes: how to obtain a reliable MTF with an automatic approach?

The purpose of this study was to assess the spatial resolution of a computed tomography (CT) scanner with an automatic approach developed for routine quality controls when varying CT parameters. The methods available to assess the modulation transfer functions (MTF) with the automatic approach were Droege's and the bead point source (BPS) methods. These MTFs were compared with presampled ones obtained using Boone's method. The results show that Droege's method is not accurate in the low-frequency range, whereas the BPS method is highly sensitive to image noise. While both methods are well adapted to routine stability controls, it was shown that they are not able to provide absolute measurements. On the other hand, Boone's method, which is robust with respect to aliasing, more resilient to noise and provides absolute measurements, satisfies the commissioning requirements perfectly. Thus, Boone's method combined with a modified Catphan 600 phantom could be a good solution to assess CT spatial resolution in the different CT planes.

Three-Dimensional (3D) Microarchitecture Correlations with 2D Projection Image Gray-Level Variations Assessed by Trabecular Bone Score Using High-Resolution Computed Tomographic Acquisitions: Effects of Resolution and Noise.

The aim of the present study is to determine the level of correlation between the 3-dimensional (3D) characteristics of trabecular bone microarchitecture, as evaluated using microcomputed tomography (μCT) reconstruction, and trabecular bone score (TBS), as evaluated using 2D projection images directly derived from 3D μCT reconstruction (TBSμCT). Moreover, we have evaluated the effects of image degradation (resolution and noise) and X-ray energy of projection on these correlations. Thirty human cadaveric vertebrae were acquired on a microscanner at an isotropic resolution of 93μm. The 3D microarchitecture parameters were obtained using MicroView (GE Healthcare, Wauwatosa, MI). The 2D projections of these 3D models were generated using the Beer-Lambert law at different X-ray energies. Degradation of image resolution was simulated (from 93 to 1488μm). Relationships between 3D microarchitecture parameters and TBSμCT at different resolutions were evaluated using linear regression analysis. Significant correlations were observed between TBSμCT and 3D microarchitecture parameters, regardless of the resolution. Correlations were detected that were strongly to intermediately positive for connectivity density (0.711≤r(2)≤0.752) and trabecular number (0.584≤r(2)≤0.648) and negative for trabecular space (-0.407 ≤r(2)≤-0.491), up to a pixel size of 1023μm. In addition, TBSμCT values were strongly correlated between each other (0.77≤r(2)≤0.96). Study results show that the correlations between TBSμCT at 93μm and 3D microarchitecture parameters are weakly impacted by the degradation of image resolution and the presence of noise.

Radiation doses in computed tomography: pitfalls in comparing CT to chest X-ray

Rapid response to : Madan M Rehani and Manorma Berry Radiation doses in computed tomography BMJ 2000; 320: 593-594

Diagnosis of right ventricular dysfunction in acute pulmonary embolism using helical computed tomography.

Forty-six consecutive patients with pulmonary embolism (PE) who underwent pulmonary angiography, helical computed tomography (CT), and echocardiography in the investigators' emergency department were studied. It was determined that the CT right ventricular (RV)/left ventricular (LV) end-diastolic area ratio was correlated with PE obstruction and echocardiography. A CT RV/LV area ratio >1 had a sensitivity of 88% and a specificity of 88% in diagnosing significant PE. The present study suggests that helical CT may be used as a triage tool in acute PE for selecting high-risk patients, using calculation of the RV/LV area ratio to detect RV dysfunction.

Assessment of glenoid inclination on routine clinical radiographs and computed tomography examinations of the shoulder.

BACKGROUND: Accurate assessment of glenoid inclination is of interest for a variety of conditions and procedures. The purpose of this study was to develop an accurate and reproducible measurement for glenoid inclination on standardized anterior-posterior (AP) radiographs and on computed tomography (CT) images. MATERIALS AND METHODS: Three consistently identifiable angles were defined: Angle α by line AB connecting the superior and inferior glenoid tubercle (glenoid fossa) and the line identifying the scapular spine; angle β by line AB and the floor of the supraspinatus fossa; angle γ by line AB and the lateral margin of the scapula. Experimental study: these 3 angles were measured in function of the scapular position to test their resistance to rotation. Conventional AP radiographs and CT scans were acquired in extension/flexion and internal/external rotation in a range up to ±40°. Clinical study: the inter-rater reliability of all angles was assessed on AP radiographs and CT scans of 60 patients (30 with proximal humeral fractures, 30 with osteoarthritis) by 2 independent observers. RESULTS: The experimental study showed that angle α and β have a resistance to rotation of up to ±20°. The deviation from neutral position was not more than ±10°. The results for the inter-rater reliability analyzed by Bland-Altman plots for the angle β fracture group were (mean ± standard deviation) -0.1 ± 4.2 for radiographs and -0.3 ± 3.3 for CT scans; and for the osteoarthritis group were -1.2 ± 3.8 for radiographs and -3.0 ± 3.6 for CT scans. CONCLUSION: Angle β is the most reproducible measurement for glenoid inclination on conventional AP radiographs, providing a resistance to positional variability of the scapula and a good inter-rater reliability.