Application of high resolution pQCT analysis for the assessment of a bone lesion: a technical note.

Peripheral quantitative computed tomography (pQCT) has found new fields of application in bone medicine, but none of them concerns the forensic practice. This study exposes the potential of pQCT applied to a penetrating lesion in a vertebral body. A pQCT scanner was used for the measurements (XCT Research SA+; Stratec Medizintechnik GmbH, Pforzheim, Germany). A more precise reconstruction of the path of the lesion within the trabecular bone was reached, with more details concerning the morphological characteristics of the lesion inside the vertebral body, and the elaboration of a 3D model was created, which allowed the operator to define the volume of the lack of tissues related to the lesion. The application of pQCT scan proved to be a potentially useful tool for the assessment of bone lesions, although further studies are needed in order to verify its applicability to forensic context.

Mapping aortic hemodynamics using 3D cine phase contrast magnetic resonance parallel imaging: evaluation of an anisotropic diffusion filter.

PURPOSE: To propose and evaluate an anisotropic diffusion filter to improve visualization and analysis of the thoracic aorta local hemodynamics from phase-contrast MRI sensitivity encoding imaging. METHODS: The filter parameters were tailored to the phase-contrast MRI sensitivity encoding data, using a simple calibration procedure. The filter was applied to 20 phase-contrast MR image studies (five subjects acquired with four different sensitivity encoding reduction factors). The filter effect was estimated with respect to image quality (noise in velocity images, σ(n)), regularity of the velocity fields (divergence; relative error in velocity magnitude, and absolute error in flow direction), aorta flow pattern visualization (streamlines, secondary flows) and flow rate quantification. RESULTS: σ(n) decreased up to three times, divergence, error in velocity magnitude, and absolute error in flow direction decreased (by at least 313, 40, and 10%, respectively), indicating less noisy and more regular velocity fields after filtering. Streamline analysis confirmed the beneficial effect of anisotropic diffusion filter, both visually and quantitatively (streamline numbers increased by 207% in whole cardiac cycle and by 180% in systolic phase). A high correlation (r = 0.99) between the prefiltering and postfiltering aortic flow rate values was found. CONCLUSION: The anisotropic diffusion filter approach can be considered effective in improving the visualization and analysis of the thoracic aorta hemodynamics from phase-contrast MRI sensitivity encoding images.

The autofocusing system of the IMAT neutron camera.

In this paper, we present the autofocusing system of the imaging instrument to be used on IMAT, a new neutron-imaging facility under construction at the ISIS (UK) target station 2. We have compared 16 different autofocus algorithms to select the one with the best performance. The algorithms have been evaluated by using both a qualitative analysis and a quantitative one. An overall score has been computed and the "contrast based" algorithm has been selected for the autofocusing system. The adopted setup together with the described autofocusing system makes the camera a user-friendly imaging device allowing the optimization of beam time use.

On the use of in vivo measured flow rates as boundary conditions for image-based hemodynamic models of the human aorta: implications for indicators of abnormal flow.

The purpose of this study is to investigate how the imposition of personalized, non-invasively measured blood flow rates as boundary conditions (BCs) influences image-based computational hemodynamic studies in the human aorta. We extracted from 4D phase-contrast MRI acquisitions of a healthy human (1) the geometry of the thoracic aorta with supra-aortic arteries and (2) flow rate waveforms at all boundaries. Flow simulations were carried out, and the implications that the imposition of different BC schemes based on the measured flow rates have on wall shear stress (WSS)-based indicators of abnormal flow were analyzed. Our results show that both the flow rate repartition among the multiple outlets of the aorta and the distribution and magnitude of the WSS-based indicators are strongly influenced by the adopted BC strategy. Keeping as reference hemodynamic model the one where the applied BC scheme allowed to obtain a satisfactory agreement between the computed and the measured flow rate waveforms, differences in WSS-based indicators up to 49% were observed when the other BC strategies were applied. In conclusion, we demonstrate that in subject-specific computational hemodynamics models of the human aorta the imposition of BC settings based on non-invasively measured flow rate waveforms influences indicators of abnormal flow to a large extent. Hence, a BCs set-up assuring realistic, subject-specific instantaneous flow rate distribution must be applied when BCs such as flow rates are prescribed.

Comparative high-resolution pQCT analysis of femoral neck indicates different bone mass distribution in osteoporosis and osteoarthritis.

SUMMARY: Osteoarthritis is linked to a reduced risk of femoral fracture despite osteoporosis. Different bone distribution in the femoral neck in osteoarthritis and fracture was revealed using a peripheral quantitative computed tomography (pQCT) comparative analysis. Our findings sustain the presence of an adaptive mechanism of bone structure providing fracture protection in osteoarthritis. INTRODUCTION: Although osteoarthritis is associated with reduced femoral fracture risk, it does not protect from bone loss. We investigated whether adaptive mechanisms are present at the arthritic joint, leading to reduced fracture risk, despite the presence of low bone mass density. METHODS: We performed pQCT comparative analyses of human femoral neck specimens derived from 32 postmenopausal women who received hip prostheses for osteoarthritis (n = 19) or femoral fracture (n = 13) by applying an in-house automated software to extract bone structure descriptors, characterize trabecular and cortical bone distribution, and evaluate their mutual relationships. RESULTS: The cortical bone volume and trabecular thickness were significantly (p < 0.05) higher in the osteoarthritis group than in the fracture group. Trabecular bone volume was also significantly (p < 0.05) higher in the osteoarthritis group than the fracture group at the inferior and anterior quadrants. Significance was maintained after adjusting for age, cortical bone volume, and cortical porosity thickness. Multiple linear regression analysis showed that thickness, volume, and apparent density of the trabecular region significantly (p < 0.05) correlated with the same cortical descriptors in osteoarthritis, but no significant relationship was found in the fracture group. Age differentially affected the mutual relationships in the two groups, showing a significant correlation with trabecular thickness in both groups and with apparent trabecular density only in femoral fracture group. CONCLUSIONS: Starting from these differences in the structural descriptors, our study sustains the presence of a compensatory mechanism in osteoarthritis to preserve the mechanical competence of bone structure, despite the loss of trabecular bone, underlying lower fracture risk.

An automatic segmentation method for regional analysis of femoral neck images acquired by pQCT.

We developed an automatic method for regional analysis of femoral neck images acquired by peripheral quantitative computed tomography (pQCT), based on automatic spatial re-alignment and segmentation; the segmentation method, based on a morphological approach, explicitly accounts for the presence of three different bone compartments: cortical region, trabecular region, and transition zone between cortical and trabecular compartments. The proposed method was applied on 13 femoral neck sections derived from female donors who were undergoing hip replacement surgery for primary degenerative arthritis or fracture, and a typical densitometric and structural analysis was performed both globally and regionally. The proposed segmentation method was quantitatively evaluated by comparing automatic contour and the corresponding manual contours delineated by three operators using metrics based on surface distance (average symmetric distance, ASD) and volumetric overlapping (dice similarity coefficient, DSC). The same approach was used to validate the automatic spatial orientation, considering as metric the difference between manual and automatic angle orientation. Results confirm a satisfactory agreement between automatic and manual performances (ASD < 0.41 mm, DSC > 0.91, orientation difference = 3.61°) and show that globally our algorithm performs very well. Concerning regional analysis application, from our results we can observe that significant differences are present among the four bone quadrants.

Elastic registration based on particle filter in radiotherapy images with brain deformations.

This paper presents the evaluation of the accuracy of an elastic registration algorithm, based on the particle filter and an optical flow process. The algorithm is applied in brain CT and MRI simulated image datasets, and MRI images from a real clinical radiotherapy case. To validate registration accuracy, standard indices for registration accuracy assessment were calculated: the dice similarity coefficient (DICE), the average symmetric distance (ASD) and the maximal distance between pixels (Dmax). The results showed that this registration process has good accuracy, both qualitatively and quantitatively, suggesting that this method may be considered as a good new option for radiotherapy applications like patient's follow up treatment.

A 3-D study of capsular invasion in follicular thyroid tumors. A novel approach to an old dilemma.

OBJECTIVE: The diagnosis of follicular tumors of the thyroid mainly rests on the examination of peri-lesional capsule. Lesions with an intact shell are labeled as adenoma, those with capsular invasion are considered carcinoma and those with doubtful aspects are regarded as tumors of uncertain malignant potential. AIM: To better understand the biology of capsular invasion and its practical implication by applying a peculiar three dimension (3-D) reconstruction. METHOD: Two follicular carcinoma (FC) and one follicular tumour of uncertain malignant potential (FT-UMP) were considered. Areas of true/doubtful capsular invasion were labeled using Tissue Micro Array technology and the corresponding paraffin blocks underwent serial sectioning. H&E slides (range 30-100, mean 70) were captured as pictures, aligned using automated method based on the maximization of mutual information and imported into a 3-D image processing software (AMIRA). RESULTS: The 3-D reconstruction revealed that capsular openings were oval shaped and sized approximately equal to 100-200 microm. In one FC the hole was entirely engaged by a tumor mass. In the remaining cases (1 FC and 1 FT-UMP) the 3-D reconstruction showed a small feeding vessel (approximately equal to 50 micro) passing through the capsule together with the bulge of the lesion [see 3-D reconstruction at http://www.ibfm. cnr.it/ricerca/inv_cap.php]. CONCLUSIONS: Our approach allows a better spatial reconstruction of the exact point of capsular interruption; the results obtained suggest that capsular invasion can be due either by abruptly interruption of the shell or by a protrusion along the path of a small feeding vessel.

Automatic segmentation of cortical and trabecular components of bone specimens acquired by pQCT.

Peripheral Quantitative Computerized Tomography (pQCT) allows the acquisition of bone specimens with a spatial resolution adequate to visualize the 3D structure of the bone cortex and the trabecular network. At present, pQCT scanners are equipped with image processing software that limits the bone analysis in two dimensions and requires strong user interaction. In this work, a method is proposed to automatically segment, in 3D, cortical and trabecular components of bone specimens acquired by pQCT, in order to facilitate and enhance the quantitative evaluation of densitometric properties of the bone.