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1.
Phys Med ; 53: 17-24, 2018 Sep.
Article in English | MEDLINE | ID: mdl-30241750

ABSTRACT

The impact of several physical quantities on the spatial resolution of an X-ray scintillating pixel detector for a micro cone beam CT (µCBCT) is investigated and discussed. The XtremeCT from SCANCO Medical AG was simulated using the EGSnrc/EGS++ Monte Carlo (MC) framework and extensively benchmarked in a previous work. The resolution of the detector was determined by simulating a titanium knife-edge to obtain the edge spread function (ESF) and the modulation transfer function (MTF). Propagation of the scintillation light through the scintillator and its coupling into the fiber optics system was taken into account. The contribution of particles scattered in the main scanner components to the detector signal is very low and does not affect the spatial resolution of the detector. The resolution obtained from the energy deposition in the scintillator without any blurring due to the propagation of the scintillation light into the fiber optics array was 31 µm. By assuming isotropic light propagation in the scintillator, the resolution degraded to 360 µm. A simple light propagation model taking into account the impact of the scintillator's columnar microstructures was developed and compared with the MANTIS Monte Carlo simulation package. By reducing the width of the model's light propagation kernel by a factor of 2 compared to the isotropic case, the detector resolution can be improved to 83 µm, which corresponds well to the measured resolution of 86 µm. The resolution of the detector is limited mainly by the propagation of the scintillation light through the scintillator layer. It offers the greatest potential to improve the resolution of the µCBCT imaging system.


Subject(s)
Cone-Beam Computed Tomography/instrumentation , Monte Carlo Method , Scintillation Counting/instrumentation , Light
2.
J Clin Densitom ; 20(2): 226-232, 2017.
Article in English | MEDLINE | ID: mdl-27956336

ABSTRACT

High-resolution peripheral quantitative computed tomography (HR-pQCT) quantifies bone microstructure and density at the distal tibia where there is also a sizable amount of myotendinous (muscle and tendon) tissue (MT); however, there is no method for the quantification of MT. This study aimed (1) to assess the feasibility of using HR-pQCT distal tibia scans to estimate MT properties using a custom algorithm, and (2) to determine the relationship between MT properties at the distal tibia and mid-leg muscle density (MD) obtained from pQCT. Postmenopausal women from the Hamilton cohort of the Canadian Multicenter Osteoporosis Study had a single-slice (2.3 ± 0.5 mm) 66% site pQCT scan measuring muscle cross-sectional area (MCSA) and MD. A standard HR-pQCT scan was acquired at the distal tibia. HR-pQCT-derived MT cross-sectional area (MTCSA) and MT density (MTD) were calculated using a custom algorithm in which thresholds (34.22-194.32 mg HA/cm3) identified muscle seed volumes and were iteratively expanded. Pearson and Bland-Altman plots were used to assess correlations and systematic differences between pQCT- and HR-pQCT-derived muscle properties. Among 45 women (mean age: 74.6 ± 8.5 years, body mass index: 25.9 ± 4.3 kg/m2), MTD was moderately correlated with mid-leg MD across the 2 modalities (r = 0.69-0.70, p < 0.01). Bland-Altman analyses revealed no evidence of directional bias for MTD-MD. HR-pQCT and pQCT measures of MTCSA and MCSA were moderately correlated (r = 0.44, p < 0.01). Bland-Altman plots for MTCSA revealed that larger MCSAs related to larger discrepancy between the distal and the mid-leg locations. This is the first study to assess the ability of HR-pQCT to measure MT size, density, and morphometry. HR-pQCT-derived MTD was moderately correlated with mid-leg MD from pQCT. This relationship suggests that distal MT may share common properties with muscle throughout the length of the leg. Future studies will assess the value of HR-pQCT-derived MT properties in the context of falls, mobility, and balance.


Subject(s)
Algorithms , Muscle, Skeletal/anatomy & histology , Muscle, Skeletal/diagnostic imaging , Tendons/anatomy & histology , Tendons/diagnostic imaging , Tomography, X-Ray Computed/methods , Aged , Aged, 80 and over , Ankle , Female , Humans , Leg , Middle Aged , Organ Size , Tibia/diagnostic imaging
3.
Med Phys ; 39(6Part4): 3625, 2012 Jun.
Article in English | MEDLINE | ID: mdl-28519505

ABSTRACT

PURPOSE: Micro CBCT scanners have a broad spectrum of applications in medicine and material science. However, CBCT suffers from scatter radiation and spectral effects such as beam hardening (BH). In this work an iterative BH- and scatter-correction algorithm was developed using Monte Carlo (MC) methods. METHODS: Two µCBCT scanner models (XtremeCT and µCT100 from SCANCO Medical AG) were simulated using EGSnrc/EGS++. The scanner measures the attenuation of X-rays passing through the phantom and interacting in a scintillating detector. The MC method is used to characterize the influence of the scattering and BH- effects. In addition, an analytical model is developed in order to correct for the scattering effect. For this purpose, by using MC methods, different scatter components were analyzed with respect to the number of scatter interactions within the given geometry. For the BH-effect, after assessing the detector response for an equivalent mono-energetic and scatter-free system using MC methods, an analytical correction model was developed. Both correction methods were implemented as an iterative reconstruction correction algorithm and were tested for various phantoms. RESULTS: MC simulations show that the amounts of correction for the scattering and BH- effects are in the same order of magnitude. The correction term for scattering effects is a function of the scatter to primary ratio only and is mainly due to single scattered particles. The contribution of multiple scattered particles to the total scatter signal is small and can be approximated by a constant. In all cases tested, the reconstructed linear attenuation coefficients converge to the mono-energetic reference values after 2-3 iteration steps with a deviation of about 1%. CONCLUSIONS: By using an iterative correction algorithm using single scatter approximation, BH- and scatter correction can be performed accurately for µCBCT scanners. This work was supported by CTI-10629.1 and SCANCO Medical AG.

4.
J Biomech ; 36(5): 671-80, 2003 May.
Article in English | MEDLINE | ID: mdl-12694997

ABSTRACT

Acute and long-term (up to 56 days) evolution of geometry, structural properties, vascular smooth muscle (VSM) tone and histomorphometric properties of the rat common carotid arteries under induced hypertension were investigated. Hypertension was induced in 8-week old male Wistar rats by total ligation of the aorta between the two kidneys. Rats were sacrificed 2, 4, 8 and 56 days postsurgery. The arterial wall layers thicken non-uniformly during the adaptation process, the inner layers thicken more in the acute phase of hypertension, whereas the outer layers of the wall are thicker than the inner layers at the end of the adaptation phase. Collagen content in the wall media exhibits a non-linear evolution, with a rapid increase in the acute hypertension phase followed by a slower increase at long-term. The elastin content increase is slight and steady, whereas VSM shows a steady but considerable increase which outdoes the collagen increase in long-term phase. VSM tone increases rapidly in the acute phase of remodelling (0-8 days) and this increase in tone contributes to a considerable increase in arterial compliance in the operating pressure range. At long-term (56 days) VSM tone returns to near control level, but compliance is even further increased, which suggests that at long-term the compliance increase is attributed primarily to structural remodelling.


Subject(s)
Carotid Artery, Common/pathology , Carotid Artery, Common/physiopathology , Hypertension/pathology , Hypertension/physiopathology , Adaptation, Physiological , Animals , Blood Pressure , Cell Count , Collagen/metabolism , Elasticity , Elastin/metabolism , Male , Muscle Tonus , Muscle, Smooth, Vascular/pathology , Muscle, Smooth, Vascular/physiopathology , Rats , Rats, Wistar
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