A semi-microscopic calculation of the potential in heavy ion collisions

A Dissertation Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg for the degree of Master of Science. Johannesburg March 197

Implantation of 3D-Printed Patient-Specific Aneurysm Models into Cadaveric Specimens: A New Training Paradigm to Allow for Improvements in Cerebrovascular Surgery and Research.

AimTo evaluate the feasibility of implanting 3D-printed brain aneurysm model in human cadavers and to assess their utility in neurosurgical research, complex case management/planning, and operative training.MethodsTwo 3D-printed aneurysm models, basilar apex and middle cerebral artery, were generated and implanted in four cadaveric specimens. The aneurysms were implanted at the same anatomical region as the modeled patient. Pterional and orbitozygomatic approaches were done on each specimen. The aneurysm implant, manipulation capabilities, and surgical clipping were evaluated.ResultsThe 3D aneurysm models were successfully implanted to the cadaveric specimens' arterial circulation in all cases. The features of the neck in terms of flexibility and its relationship with other arterial branches allowed for the practice of surgical maneuvering characteristic to aneurysm clipping. Furthermore, the relationship of the aneurysm dome with the surrounding structures allowed for better understanding of the aneurysmal local mass effect. Noticeably, all of these observations were done in a realistic environment provided by our customized embalming model for neurosurgical simulation.Conclusion3D aneurysms models implanted in cadaveric specimens may represent an untapped training method for replicating clip technique; for practicing certain approaches to aneurysms specific to a particular patient; and for improving neurosurgical research

Contrast material–enhanced MRA overestimates severity of carotid stenosis, compared with 3D time-of-flight MRA

AbstractObjectiveNon–contrast-enhanced magnetic resonance angiography (MRA) carotid imaging with the time-of-flight (TOF) technique compares favorably with angiography, ultrasound, and excised plaques. However, gadolinium contrast-enhanced MRA (CE-MRA) has almost universally replaced TOF-MRA, because it reduces imaging time (25 seconds vs 10 minutes) and improves signal-to-noise ratio. In our practice we found alarming discrepancies between CE-MRA and TOF-MRA, which was the impetus for this study.Study designTo compare the two techniques, we measured stenosis, demonstrated on three-dimensional images obtained at TOF and CE-MRA, in 107 carotid arteries in 58 male patients. The measurements were made on a Cemax workstation equipped with enlargement and measurement tools. Measurements to 0.1 mm were made at 90 degrees to the flow channel at the area of maximal stenosis and distal to the bulb where the borders of the internal carotid artery lumen were judged to be parallel (North American Symptomatic Carotid Endarterectomy Trial criteria). Experiments with carotid phantoms were done to test the comtribution of imaging software to image quality.ResultsTwelve arteries were occluded. In the remaining 95 arteries, compared with TOF-MRA, CE-MRA demonstrated a greater degree of stenosis in 42 arteries, a lesser degree of stenosis in 14 arteries, and similar (±5%) stenosis in 39 arteries (P = .02, χ2 analysis). The largest discrepancies were arteries with 0% to 70% stenosis. In those arteries in which CE-MRA identified a greater degree of stenosis than shown with TOF-MRA, mean increase was 21% for 0% to 29% stenosis, 36% for 30% to 49% stenosis, and 38% for of 50% to 69% stenosis. The carotid phantom experiments showed that the imaging parameters of CE-MRA, particularly the plane on which frequency encoding gradients were applied, reduced signal acquisition at the area of stenosis.ConclusionsCollectively these data demonstrate that CE-MRA parameters must be retooled if the method is to be considered reliable for determination of severity of carotid artery stenosis. CE-MRA is an excellent screening technique, but only TOF-MRA should be used to determine degree of carotid artery stenosis

Short term doxycycline treatment induces sustained improvement in myocardial infarction border zone contractility.

Decreased contractility in the non-ischemic border zone surrounding a MI is in part due to degradation of cardiomyocyte sarcomeric components by intracellular matrix metalloproteinase-2 (MMP-2). We recently reported that MMP-2 levels were increased in the border zone after a MI and that treatment with doxycycline for two weeks after MI was associated with normalization of MMP-2 levels and improvement in ex-vivo contractile protein developed force in the myocardial border zone. The purpose of the current study was to determine if there is a sustained effect of short term treatment with doxycycline (Dox) on border zone function in a large animal model of antero-apical myocardial infarction (MI). Antero-apical MI was created in 14 sheep. Seven sheep received doxycycline 0.8 mg/kg/hr IV for two weeks. Cardiac MRI was performed two weeks before, and then two and six weeks after MI. Two sheep died prior to MRI at six weeks from surgical/anesthesia-related causes. The remaining 12 sheep completed the protocol. Doxycycline induced a sustained reduction in intracellular MMP-2 by Western blot (3649±643 MI+Dox vs 9236±114 MI relative intensity; p = 0.0009), an improvement in ex-vivo contractility (65.3±2.0 MI+Dox vs 39.7±0.8 MI mN/mm2; p<0.0001) and an increase in ventricular wall thickness at end-systole 1.0 cm from the infarct edge (12.4±0.6 MI+Dox vs 10.0±0.5 MI mm; p = 0.0095). Administration of doxycycline for a limited two week period is associated with a sustained improvement in ex-vivo contractility and an increase in wall thickness at end-systole in the border zone six weeks after MI. These findings were associated with a reduction in intracellular MMP-2 activity

Double-lumen carotid plaque: A morbid configuration

AbstractDuring analysis of carotid plaque anatomy for a multicenter carotid imaging trial, we examined plaque specimens from 5 patients with double internal carotid artery lumina. Four of the 5 patients had symptoms referable to the lesion. The second lumen was noted when the plaque specimens were examined ex vivo with high-resolution (200 μm3) magnetic resonance imaging. Plaque structure was correctly identified in only 1 patient preoperatively. However, during retrospective review of the preoperative imaging studies, the second internal carotid artery lumen was identified in 3 patients

Implantation of 3D-Printed Patient-Specific Aneurysm Models into Cadaveric Specimens: A New Training Paradigm to Allow for Improvements in Cerebrovascular Surgery and Research

Aim. To evaluate the feasibility of implanting 3D-printed brain aneurysm model in human cadavers and to assess their utility in neurosurgical research, complex case management/planning, and operative training. Methods. Two 3D-printed aneurysm models, basilar apex and middle cerebral artery, were generated and implanted in four cadaveric specimens. The aneurysms were implanted at the same anatomical region as the modeled patient. Pterional and orbitozygomatic approaches were done on each specimen. The aneurysm implant, manipulation capabilities, and surgical clipping were evaluated. Results. The 3D aneurysm models were successfully implanted to the cadaveric specimens’ arterial circulation in all cases. The features of the neck in terms of flexibility and its relationship with other arterial branches allowed for the practice of surgical maneuvering characteristic to aneurysm clipping. Furthermore, the relationship of the aneurysm dome with the surrounding structures allowed for better understanding of the aneurysmal local mass effect. Noticeably, all of these observations were done in a realistic environment provided by our customized embalming model for neurosurgical simulation. Conclusion. 3D aneurysms models implanted in cadaveric specimens may represent an untapped training method for replicating clip technique; for practicing certain approaches to aneurysms specific to a particular patient; and for improving neurosurgical research

Carotid Atheroma Rupture Observed In Vivo and FSI-Predicted Stress Distribution Based on Pre-rupture Imaging

Atherosclerosis at the carotid bifurcation is a major risk factor for stroke. As mechanical forces may impact lesion stability, finite element studies have been conducted on models of diseased vessels to elucidate the effects of lesion characteristics on the stresses within plaque materials. It is hoped that patient-specific biomechanical analyses may serve clinically to assess the rupture potential for any particular lesion, allowing better stratification of patients into the most appropriate treatments. Due to a sparsity of in vivo plaque rupture data, the relationship between various mechanical descriptors such as stresses or strains and rupture vulnerability is incompletely known, and the patient-specific utility of biomechanical analyses is unclear. In this article, we present a comparison between carotid atheroma rupture observed in vivo and the plaque stress distribution from fluid–structure interaction analysis based on pre-rupture medical imaging. The effects of image resolution are explored and the calculated stress fields are shown to vary by as much as 50% with sub-pixel geometric uncertainty. Within these bounds, we find a region of pronounced elevation in stress within the fibrous plaque layer of the lesion with a location and extent corresponding to that of the observed site of plaque rupture