Senthil Ramamurthy

Hemodynamic predictors of aortic dilatation in bicuspid aortic valve by velocity-encoded cardiovascular magnetic resonance

BackgroundCongenital Bicuspid Aortic Valve (BAV) is a significant risk factor for serious complications including valve dysfunction, aortic dilatation, dissection, and sudden death. Clinical tools for identification and monitoring of BAV patients at high risk for development of aortic dilatation, an early complication, are not available.MethodsThis paper reports an investigation in 18 pediatric BAV patients and 10 normal controls of links between abnormal blood flow patterns in the ascending aorta and aortic dilatation using velocity-encoded cardiovascular magnetic resonance. Blood flow patterns were quantitatively expressed in the angle between systolic left ventricular outflow and the aortic root channel axis, and also correlated with known biochemical markers of vessel wall disease.ResultsThe data confirm larger ascending aortas in BAV patients than in controls, and show more angled LV outflow in BAV (17.54 ± 0.87 degrees) than controls (10.01 ± 1.29) (p = 0.01). Significant correlation of systolic LV outflow jet angles with dilatation was found at different levels of the aorta in BAV patients STJ: r = 0.386 (N = 18, p = 0.048), AAO: r = 0.536 (N = 18, p = 0.022), and stronger correlation was found with patients and controls combined into one population: SOV: r = 0.405 (N = 28, p = 0.033), STJ: r = 0.562 (N = 28, p = 0.002), and AAO r = 0.645 (N = 28, p < 0.001). Dilatation and the flow jet angle were also found to correlate with plasma levels of matrix metallo-proteinase 2.ConclusionsThe results of this study provide new insights into the pathophysiological processes underlying aortic dilatation in BAV patients. These results show a possible path towards the development of clinical risk stratification protocols in order to reduce morbidity and mortality for this common congenital heart defect.

Integrating Patient Digital Photographs with Medical Imaging Examinations

We introduce the concept, benefits, and general architecture for acquiring, storing, and displaying digital photographs along with medical imaging examinations. We also discuss a specific implementation built around an Android-based system for simultaneously acquiring digital photographs along with portable radiographs. By an innovative application of radiofrequency identification technology to radiographic cassettes, the system is able to maintain a tight relationship between these photographs and the radiographs within the picture archiving and communications system (PACS) environment. We provide a cost analysis demonstrating the economic feasibility of this technology. Since our architecture naturally integrates with patient identification methods, we also address patient privacy issues.

“PINOT”: Time-resolved parallel magnetic resonance imaging with a reduced dynamic field of view

This article introduces a novel method named “Parallel Imaging and Noquist in Tandem” (PINOT) for accelerated image acquisition of cine cardiac magnetic resonance imaging. This method combines two prior information formalisms, the SPACE‐RIP implementation of parallel imaging and the Noquist method for reduced‐data image reconstruction with prior knowledge of static and dynamic regions in the field of view. The general theory is presented, and supported by results from experiments using time‐resolved two‐dimensional simulation data and retrospectively sub‐sampled magnetic resonance imaging data with acceleration factors around 4. A signal‐to‐noise ratio analysis and a comparison study with TSENSE and k‐t SENSE show that PINOT performs favorably in preserving edge detail, at a cost in signal‐to‐noise ratio and computational complexity. Magn Reson Med, 2010.

Sampling strategies for super-resolution in multi-slice MRI

A comparison study is presented of two methods for MRI reconstruction using super-resolution techniques which combine multiple multi-slice stacks into a single high- resolution 3-D image volume. Sampling configurations are compared involving stacks with parallel orientations at different sub-pixel offset locations, and stacks with regularly distributed slice orientations. Results from experiments with simulated and real MRI data suggest that different stack orientations perform better than parallel stacks.

Quantification and origin of differential pulmonary blood flow in patients with a Fontan circulation

Methods Patients with a Fontan circulation were prospectively consented to undergo three dimensional phase contrast (4Dflow) imaging during a clinical cardiac MRI evaluation which also included standard two dimensional phase contrast (2D-PC) imaging of all pertinent vessels. Differential pulmonary blood flow was calculated using standard 2D-PC imaging of the right and left pulmonary arteries (RPA and LPA). On the 4Dflow datasets, an expert reader defined cross sections of the RPA, LPA, and the superior and inferior venae cavae (SVC and IVC) within the Fontan circuit using prototype 4Dflow software (Siemens Healthcare, Erlangen, Germany). These defined the analysis and seed planes respectively. Particles were emitted from either the SVC or IVC plane, and quantification was performed at the outlets using the 4Dflow software. The 3D pathlines were then exported for further analysis. Custom software was written in MATLAB (Mathworks, Natick, MA) for flow quantification. The terminal spatial position of each particle was determined. The number of particles that crossed into the RPA and LPA were counted. The differential pulmonary blood flow was calculated for each simulation as the ratio of particles in the RPA to LPA. Internal consistency of the 4Dflow measurements was validated using conservation of mass analysis. Systemic venous flow by origin (IVC or SVC) and total systemic venous flow into each branch PA were calculated. Preferential flow was defined as flow > 70% into one of the branch PAs.

Background phase correction in congenital heart disease: does reliability vary based on underlying disease type?

Background Phase-contrast magnetic resonance (PC-MR) allows non-invasive calculation of vascular flow, peak velocities and shunts. The technique, however, has inherent limitations, one of which is background phase errors. Various background phase correction (BPC) algorithms have been developed. The aim of this study is to apply various commercially available BPC algorithms in pediatric patients with a variety of disease types.

TU-F-18C-03: X-Ray Scatter Correction in Breast CT: Advances and Patient Testing

PURPOSE To further develop and perform patient testing of an x-ray scatter correction algorithm for dedicated breast computed tomography (BCT). METHODS A previously proposed algorithm for x-ray scatter signal reduction in BCT imaging was modified and tested with a phantom and on patients. A wireless electronic positioner system was designed and added to the BCT system that positions a tungsten plate in and out of the x-ray beam. The interpolation used by the algorithm was replaced with a radial basis function-based algorithm, with automated exclusion of non-valid sampled points due to patient motion or other factors. A 3D adaptive noise reduction filter was also introduced to reduce the impact of scatter quantum noise post-reconstruction. The impact on image quality of the improved algorithm was evaluated using a breast phantom and seven patient breasts, using quantitative metrics such signal difference (SD) and signal difference-to-noise ratios (SDNR) and qualitatively using image profiles. RESULTS The improvements in the algorithm resulted in a more robust interpolation step, with no introduction of image artifacts, especially at the imaged object boundaries, which was an issue in the previous implementation. Qualitative evaluation of the reconstructed slices and corresponding profiles show excellent homogeneity of both the background and the higher density features throughout the whole imaged object, as well as increased accuracy in the Hounsfield Units (HU) values of the tissues. Profiles also demonstrate substantial increase in both SD and SDNR between glandular and adipose regions compared to both the uncorrected and system-corrected images. CONCLUSION The improved scatter correction algorithm can be reliably used during patient BCT acquisitions with no introduction of artifacts, resulting in substantial improvement in image quality. Its impact on actual clinical performance needs to be evaluated in the future. Research Agreement, Koning Corp., Hologic Inc., Barco Corp Consultant Agreement, Fujifilm Medical Systems.

Time-resolved parallel imaging with a reduced dynamic field of view

This paper introduces a novel method for accelerated dynamic image acquisition for cardiac MRI. This method combines two different formalisms for reconstruction from sparse data by incorporation of prior information. Parallel imaging uses information about coil geometry in imaging systems with multiple receiver coils. Reduced field of view (rFOV) imaging exploits knowledge about static regions in a dynamic image scene. The novel method combines the SPACE-RIP implementation of parallel imaging with the Noquist rFOV imaging method, which both use a direct inversion model for image reconstruction. The theory is presented for integrated application of these methods, and results are presented of supporting experiments with simulated and real MRI data, retrospectively subsampled to generate sparse data sets. Successful application of the method confirms multiplicative combined acceleration.