Computed Tomography Scanner For Dynamic Vascular Imaging In Vitro

A dynamic computed-tomography (CT) scanner has been developed for imaging objects undergoing periodic motion. The scanner has high spatial resolution and sufficiently high temporal resolution to produce quantitative tomographic images of objects, such as excised arterial samples perfused under physiological pressure conditions.;The dynamic CT scanner is comprised of a modified x-ray image intensifier (XRII) coupled to a 1024-element linear photo-diode-array detector. The XRII was modified to allow continuous electro-optical magnification of the field-of-view, thereby increasing the system\u27s limiting resolution. High-resolution gated projection radiographs of a single slice are acquired at the rate of 60 Hz, as the object undergoes periodic motion. If the moving object is rotated through 180{dollar}\sp\circ{dollar}, and projections are obtained at many view angles, tomographic images at different phases of the object\u27s motion cycle can be reconstructed. Performance evaluation of the scanner showed that tomographic images can be obtained with resolution as high as 3.2 mm{dollar}\sp{lcub}-1{rcub}{dollar}, with only a 9% decrease in the resolution limit for objects moving at 1 cm s{dollar}\sp{lcub}-1{rcub}{dollar}. Quantitative measurements of attenuation coefficient are obtained with an accuracy of {dollar}\pm{dollar}0.02 cm{dollar}\sp{lcub}-1{rcub}{dollar}, and the accuracy in geometrical measurements of perimeter is {dollar}\pm{dollar}0.3 mm.;To evaluate the application of the system for imaging of intact excised vascular specimens under simulated physiological conditions, a computer-controlled flow simulator was built and used in the measurement of dynamic arterial distensibility. The flow simulator can reproduce physiological flow waveforms (including waveforms with reverse components) with a precision of {dollar}\pm{dollar}0.1 ml s{dollar}\sp{lcub}-1{rcub}{dollar}.;Existing techniques for the measurement of the static and dynamic elastic properties of excised vessels were adapted to take advantage of the additional data from the CT images and were used to demonstrate the utility of the CT scanner for applications in vascular research. Using these techniques, the local static and dynamic circumferential modulus of elasticity can be measured in intact arterial samples. Since the imaging technique is non-destructive, the mechanical properties of these vessels can be correlated directly with the composition of the vascular wail. This new system, together with the described techniques, offers a unique opportunity for studying dynamic events in vitro

A magnetic-resonance-imaging-compatible remote catheter navigation system.

A remote catheter navigation system compatible with magnetic resonance imaging (MRI) has been developed to facilitate MRI-guided catheterization procedures. The interventionalist\u27s conventional motions (axial motion and rotation) on an input catheter - acting as the master - are measured by a pair of optical encoders, and a custom embedded system relays the motions to a pair of ultrasonic motors. The ultrasonic motors drive the patient catheter (slave) within the MRI scanner, replicating the motion of the input catheter. The performance of the remote catheter navigation system was evaluated in terms of accuracy and delay of motion replication outside and within the bore of the magnet. While inside the scanner bore, motion accuracy was characterized during the acquisition of frequently used imaging sequences, including real-time gradient echo. The effect of the catheter navigation system on image signal-to-noise ratio (SNR) was also evaluated. The results show that the master-slave system has a maximum time delay of 41 ± 21 ms in replicating motion; an absolute value error of 2 ± 2° was measured for radial catheter motion replication over 360° and 1.0 ± 0.8 mm in axial catheter motion replication over 100 mm of travel. The worst-case SNR drop was observed to be 2.5%

Design and evaluation of an MRI-compatible linear motion stage.

PURPOSE: To develop and evaluate a tool for accurate, reproducible, and programmable motion control of imaging phantoms for use in motion sensitive magnetic resonance imaging (MRI) appli cations. METHODS: In this paper, the authors introduce a compact linear motion stage that is made of nonmagnetic material and is actuated with an ultrasonic motor. The stage can be positioned at arbitrary positions and orientations inside the scanner bore to move, push, or pull arbitrary phantoms. Using optical trackers, measuring microscopes, and navigators, the accuracy of the stage in motion control was evaluated. Also, the effect of the stage on image signal-to-noise ratio (SNR), artifacts, and B0 field homogeneity was evaluated. RESULTS: The error of the stage in reaching fixed positions was 0.025 ± 0.021 mm. In execution of dynamic motion profiles, the worst-case normalized root mean squared error was below 7% (for frequencies below 0.33 Hz). Experiments demonstrated that the stage did not introduce artifacts nor did it degrade the image SNR. The effect of the stage on the B0 field was less than 2 ppm. CONCLUSIONS: The results of the experiments indicate that the proposed system is MRI-compatible and can create reliable and reproducible motion that may be used for validation and assessment of motion related MRI applications

Effect of Left Atrial Wall Thickness on Radiofrequency Ablation Success.

INTRODUCTION: Radiofrequency (RF) ablation in thicker regions of the left atrium (LA) may require increased ablation energy in order to achieve effective transmural lesions. Consequently, many cases of recurrent atrial fibrillation (AF) postablation may be due to thicker-than-normal atrial tissue. The aim of this study was to test the hypotheses that patients with recurrent AF have thicker tissue overall and that electrical reconnection is more likely in regions of thicker tissue. METHODS AND RESULTS: Retrospective analysis was performed on 86 CT images acquired preoperatively from a cohort of 119 patients who had undergone RF ablation for AF. Of these, 33 patients experienced recurrence of AF within 1 year of initial treatment and 29 returned for a repeat ablation. For each patient, LA wall thickness (LAWT) was measured from the images in 12 anatomical regions using custom software. Patients with recurrent AF had larger LAWT compared to successfully treated patients (1.6 ± 0.6 mm vs. 1.5 ± 0.5 mm, P \u3c 0.001) and reconnection was found to be at regions of thicker tissue (1.6 ± 0.6 mm, P = 0.038) compared to nonreconnected regions (1.5 ± 0.5 mm). The superior right posterior wall of the LA was significantly related to both recurrence (P = 0.048) and reconnection (P = 0.014). CONCLUSION: Increased LAWT has a small but significant effect on postablation recurrence and reconnection. Measures of LAWT may facilitate appropriate dosing of RF energy, but other factors will be critical in transmural lesion formation and ablation success

Design and Evaluation of a Catheter Contact-Force Controller for Cardiac Ablation Therapy.

GOAL: Maintaining a constant contact force (CF) of an ablation catheter during cardiac catheter ablation therapy is clinically challenging due to inherent myocardial motion, often resulting in poor ablation of arrhythmogenic substrates. To enable a prescribed contact force to be applied during ablation, a catheter contact force controller (CCFC) was developed. METHODS: The system includes a hand-held device attached to a commercial catheter and steerable sheath. A compact linear motor assembly attaches to an ablation catheter and autonomously controls its relative position within the shaft of the steerable sheath. A closed-loop control system is implemented within embedded electronics to enable real-time catheter-tissue contact force control. To evaluate the performance of the CCFC, a linear motion phantom was used to impose a series of physiological CF profiles; lesion CF was controlled at prescribed levels ranging from 15 to 40 g. RESULTS: For a prescribed CF of 25 g, the CCFC was able to regulate the CF with a root mean squared error of 3.7 ± 0.7 g. The ability of the CCFC to retract the catheter upon sudden changes in tissue motion, which may have caused tissue damage, was also demonstrated. Finally, the device was able to regulate the CF for a predetermined amount of time according to a force-time integral model. CONCLUSION: The developed CCFC is capable of regulating catheter-tissue CF in a laboratory setting that mimics clinical ablation therapy. SIGNIFICANCE: Catheter-tissue CF control promises to improve the precision and success of ablation lesion delivery

Influence of phase correction of late gadolinium enhancement images on scar signal quantification in patients with ischemic and non-ischemic cardiomyopathy

© 2015 Stirrat et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License. Background: Myocardial fibrosis imaging using late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) has been validated as a quantitative predictive marker for response to medical, surgical, and device therapy. To date, all such studies have examined conventional, non-phase corrected magnitude images. However, contemporary practice has rapdily adopted phase-corrected image reconstruction. We sought to investigate the existence of any systematic bias between threshold-based scar quantification performed on conventional magnitude inversion recovery (MIR) and matched phase sensitive inversion recovery (PSIR) images. Methods: In 80 patients with confirmed ischemic (N=40), or non-ischemic (n=40) myocardial fibrosis, and also in a healthy control cohort (N=40) without fibrosis, myocardial late enhancement was quantified using a Signal Threshold Versus Reference Myocardium technique (STRM) at ≥2, ≥3, and ≥5 SD threshold, and also using the Full Width at Half Maximal (FWHM) technique. This was performed on both MIR and PSIR images and values compared using linear regression and Bland-Altman analyses. Results: Linear regression analysis demonstrated excellent correlation for scar volumes between MIR and PSIR images at all three STRM signal thresholds for the ischemic (N=40, r=0.96, 0.95, 0.88 at 2, 3, and 5 SD, p\u3c0.0001 for all regressions), and non ischemic (N=40, r=0.86, 0.89, 0.90 at 2, 3, and 5 SD, p\u3c0.0001 for all regressions) cohorts. FWHM analysis demonstrated good correlation in the ischemic population (N=40, r=0.83, p\u3c0.0001). Bland-Altman analysis demonstrated a systematic bias with MIR images showing higher values than PSIR for ischemic (3.3 %, 3.9 % and 4.9 % at 2, 3, and 5 SD, respectively), and non-ischemic (9.7 %, 7.4 % and 4.1 % at ≥2, ≥3, and ≥5 SD thresholds, respectively) cohorts. Background myocardial signal measured in the control population demonstrated a similar bias of 4.4 %, 2.6 % and 0.7 % of the LV volume at 2, 3 and 5 SD thresholds, respectively. The bias observed using FWHM analysis was -6.9 %. Conclusions: Scar quantification using phase corrected (PSIR) images achieves values highly correlated to those obtained on non-corrected (MIR) images. However, a systematic bias exists that appears exaggerated in non-ischemic cohorts. Such bias should be considered when comparing or translating knowledge between MIR- and PSIR-based imaging

Shape complexes: the intersection of label orderings and star convexity constraints in continuous max-flow medical image segmentation.

Optimization-based segmentation approaches deriving from discrete graph-cuts and continuous max-flow have become increasingly nuanced, allowing for topological and geometric constraints on the resulting segmentation while retaining global optimality. However, these two considerations, topological and geometric, have yet to be combined in a unified manner. The concept of shape complexes, which combine geodesic star convexity with extendable continuous max-flow solvers, is presented. These shape complexes allow more complicated shapes to be created through the use of multiple labels and super-labels, with geodesic star convexity governed by a topological ordering. These problems can be optimized using extendable continuous max-flow solvers. Previous approaches required computationally expensive coordinate system warping, which are ill-defined and ambiguous in the general case. These shape complexes are demonstrated in a set of synthetic images as well as vessel segmentation in ultrasound, valve segmentation in ultrasound, and atrial wall segmentation from contrast-enhanced CT. Shape complexes represent an extendable tool alongside other continuous max-flow methods that may be suitable for a wide range of medical image segmentation problems

Dual-energy computed tomography using a gantry-based preclinical cone-beam microcomputed tomography scanner

© The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. Dual-energy microcomputed tomography (DECT) can provide quantitative information about specific materials of interest, facilitating automated segmentation, and visualization of complex three-dimensional tissues. It is possible to implement DECT on currently available preclinical gantry-based cone-beam micro-CT scanners; however, optimal decomposition image quality requires customized spectral shaping (through added filtration), optimized acquisition protocols, and elimination of misregistration artifacts. We present a method for the fabrication of customized x-ray filters - in both shape and elemental composition - needed for spectral shaping. Fiducial markers, integrated within the sample holder, were used to ensure accurate co-registration between sequential low- and high-energy image volumes. The entire acquisition process was automated through the use of a motorized filter-exchange mechanism. We describe the design, implementation, and evaluation of a DECT system on a gantry-based-preclinical cone-beam micro-CT scanner