Numerical simulation techniques to study the structural response of the human chest following median sternotomy.

BACKGROUND: The optimal closure technique of median sternotomy remains controversial. The objective of this study was to analyze the structural response of the separated sternum using computer-based numerical discretization techniques, such as finite element methods. METHODS: Thoracic computer tomographic scans (2.5-mm slices) were segmented, analyzed by image processing techniques, and transferred into a three-dimensional finite element model. In a first approach a linear elastic material model was used; neglecting nonlinear and damage effects of the bones. The influence of muscles and tendons was disregarded. Nonlinear contact conditions were applied between the two sternal parts and between fixation wires and sternum. The structural response of this model was investigated under normal breathing and asymmetric leaning on one side of the chest. Displacement and stress response of the segmented sternum were compared regarding two different closure techniques (single loop, figure-of-eight). RESULTS: The obtained results revealed that for the normal breathing load case the single loop technique is capable of clamping the sternum sufficiently, assuming that the wires are prestressed. For asymmetric loading conditions, such as leaning on one side of the chest, the figure-of-eight loop can substantially reduce the relative longitudinal displacement between the two parts compared with the single loop. CONCLUSIONS: The application of numerical simulation techniques using complex computer models enabled the determination of structural behavior of the chest regarding the influence of different closure techniques. They allowed easy and fast modifications and therefore, in contrast to a real physical model, in-depth parameter studies.

Correlation of early dynamic CT perfusion imaging with whole-brain MR diffusion and perfusion imaging in acute hemispheric stroke.

BACKGROUND AND PURPOSE: Compared with MR imaging, dynamic CT perfusion imaging covers only a fraction of the whole brain. An important assumption is that CT perfusion abnormalities correlate with total ischemic volume. The purpose of our study was to measure the degree of correlation between abnormalities seen on CT perfusion scans and the volumes of abnormality seen on MR diffusion and perfusion images in patients with acute large-vessel stroke. METHODS: Fourteen patients with acute hemispheric stroke symptoms less than 12 hours in duration were studied with single-slice CT perfusion imaging and multislice MR diffusion and perfusion imaging. CT and MR perfusion studies were completed within 2.5 hours of one another (mean, 77 minutes) and were reviewed independently by two neuroradiologists. Hemodynamic parameters included cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). Extents of abnormality on images were compared by using Kendall correlation. RESULTS: Statistically significant correlation was found between CT-CBF and MR-CBF abnormalities (tau = 0.60, P =.003) and CT-MTT and MR-MTT abnormalities (tau = 0.65, P =.001). Correlation of CT-CBV with MR-CBV approached significance (tau = 0.39, P =.06). Extent of initial hyperintensity on diffusion-weighted images correlated best with extent of MR-CBV abnormality (tau = 0.69, P =.001), extent of MR-MTT abnormality (tau = 0.67, P =.002), and extent of CT-CBV abnormality (tau = 0.47, P =.02). CONCLUSION: Good correlation was seen between CT and MR for CBF and MTT abnormalities. It remains uncertain whether CT perfusion CBV abnormalities correspond well to whole-brain abnormalities.

A manipulator system for 14-gauge large core breast biopsies inside a high-field whole-body MR scanner.

PURPOSE: To investigate a robotic manipulator system for MR-guided breast biopsies inside a 1.5 T whole-body magnet. MATERIALS AND METHODS: Fourteen patients with suspicious breast lesions (diameter 18.6 +/- 12 mm) underwent biopsy. Patients with malignant findings underwent surgery afterwards and the histologic findings between biopsy and surgery were correlated. RESULTS: In five patients biopsy findings were histopathologically confirmed following open surgery. One tubular carcinoma was missed; one invasive cancer was underestimated. Seven patients with benign findings are still in the follow-up period. CONCLUSION: The study demonstrates the feasibility to perform breast biopsies inside the magnet of a whole-body MR scanner by using a manipulator system.

Dedicated double breast coil for magnetic resonance mammography imaging, biopsy, and preoperative localization.

RATIONALE AND OBJECTIVES: The aim of this study was to compare the performance of a dedicated double breast coil for MR imaging and intervention with a standard diagnostic double breast coil. MATERIALS AND METHODS: Signal-to-noise ratios (SNRs) were determined for both coils by using a water phantom. Fourteen patients were examined, 11 underwent preoperative hookwire localization, two were biopsied, and one received diagnostic imaging. Breast images were acquired in three patients with both coils and were visually compared. Harvested specimen from the biopsies and surgeries following hookwire localization were histopathologically evaluated. RESULTS: SNR was superior with the interventional coil in the posterior (axillary) part of the imaging volume and inferior in the anterior part compared with the standard coil. Anatomic MR breast images were of similar diagnostic quality. For the two biopsy procedures the trocar was correctly placed in front of the suspicious lesion. Hookwires were correctly located inside the lesion in nine patients and in contact with the lesion in one patient. In one patient a 2 mm distance between the lesion and the wire was observed. CONCLUSIONS: Diagnostic imaging followed by subsequent MR-guided intervention is possible within a single session by using the dedicated interventional coil. The correct final position of the hookwires demonstrates the precision of the MR guided localization procedure.

CT perfusion scanning with deconvolution analysis: pilot study in patients with acute middle cerebral artery stroke.

PURPOSE: To measure mean cerebral blood flow (CBF) in ischemic and nonischemic territories and in low-attenuation regions in patients with acute stroke by using deconvolution-derived hemodynamic imaging. MATERIALS AND METHODS: Twelve patients with acute middle cerebral artery stroke and 12 control patients were examined by using single-section computed tomography (CT) perfusion scanning. Analysis was performed with a deconvolution-based algorithm. Comparisons of mean CBF, cerebral blood volume (CBV), and mean transit time (MTT) were determined between hemispheres in all patients and between low- and normal-attenuation regions in patients with acute stroke. Two independent readers examined the images for extent of visually apparent regional perfusion abnormalities. The data were compared with extent of final infarct in seven patients with acute stroke who underwent follow-up CT or magnetic resonance imaging. RESULTS: Significant decreases in CBF (-50%, P =.001) were found in the affected hemispheres of patients with acute stroke. Significant changes in CBV (-26%, P =.03) and MTT (+111%, P =.004) were also seen. Significant alterations in perfusion were also seen in low- compared with normal-attenuation areas. Pearson correlation between readers for extent of CBF abnormality was 0.94 (P =.001). Intraobserver variation was 8.9% for CBF abnormalities. CONCLUSION: Deconvolution analysis of CT perfusion data is a promising method for evaluation of cerebral hemodynamics in patients with acute stroke.