Niranjan Venugopal

Cardiorespiratory fitness and adiposity in metabolically healthy overweight and obese youth.

OBJECTIVE: Controversy exists surrounding the contribution of fitness and adiposity as determinants of the Metabolically Healthy Overweight (MHO) phenotype in youth. This study investigated the independent contribution of cardiorespiratory fitness and adiposity to the MHO phenotype among overweight and obese youth. METHODS: This cross-sectional study included 108 overweight and obese youth classified as MHO (no cardiometabolic risk factors) or non-MHO (≥1 cardiometabolic risk factor), based on age- and gender-specific cut-points for fasting glucose, triglycerides, high-density lipoprotein cholesterol, systolic and diastolic blood pressure, and hepatic steatosis. RESULTS: Twenty-five percent of overweight and obese youth were classified as MHO. This phenotype was associated with lower BMI z-score (BMI z-score: 1.8 ± 0.3 vs 2.1 ± 0.4, P = .02) and waist circumference (99.7 ± 13.2 vs 106.1 ± 13.7 cm, P = .04) compared with non-MHO youth. When matched for fitness level and stratified by BMI z-score (1.6 ± 0.3 vs 2.4 ± 0.2), the prevalence of MHO was fourfold higher in the low BMI z-score group (27% vs 7%; P = .03). Multiple logistic regression analyses revealed that the best predictor of MHO was the absence of hepatic steatosis even after adjusting for waist circumference (odds ratio 0.57, 95% confidence interval 0.40–0.80) or BMI z-score (odds ratio 0.59, 95% confidence interval 0.43–0.80). CONCLUSIONS: The MHO phenotype was present in 25% of overweight and obese youth and is strongly associated with lower levels of adiposity, and the absence of hepatic steatosis, but not with cardiorespiratory fitness.

A feasibility study to investigate the use of thin-plate splines to account for prostate deformation

Image registration is an important step in the radiotherapy treatment planning process. It provides a method of fusing different types of diagnostic imaging information. One such application is to combine magnetic resonance spectroscopic images (MRSI) of the prostate with anatomical MRI and/or computed tomography images that are routinely used in the radiation treatment planning of prostate cancer. MRSI provides in vivo information related to the underlying metabolic activity of tissues, and can be related to the presence of cancer. However, the inflated endorectal coil required during MRS imaging poses a potential problem by deforming the prostate when it is filled with approximately 100 cm3 of air during image acquisition. This pushes the prostate superiorly/anteriorly, deforming the prostate and consequently the spectroscopic imaging data in a nonlinear manner. In this application, the coil-deformed MRS images are warped back to a non-deformed state, using a single data set. A nonlinear warping algorithm is presented to achieve this. Results indicate that the algorithm attains an accuracy of 97% (4 cm3 difference) when reproducing the total prostate volume compared to a Radiation Oncologist defined prostate volume. This difference is slightly smaller than the measured intra-operator variance of +/-1.5 cm3 (deflated coil) and the measured algorithm variance of +/-1.0 cm3. Additionally, intraprostatic nodules were used to assess the accuracy of the warping algorithm in regions inside the prostate. While choosing anatomical tie points along the external prostate surface, analysis of the nodules revealed the algorithm accuracy reduced to 63-93%.

Semi automatic MRI prostate segmentation based on wavelet multiscale products

Currently, prostate cancer is the third leading cause of cancer-related deaths among men in North America. As with many others types of cancer, early detection and treatment greatly increases the patients chance of survival. MRI prostate segmentation allows clinical personnel to design an accurate treatment plan. A novel method for MRI prostate imagery segmentation is proposed in this paper. This method exploits the different behavior presented by signal singularities and noise in the wavelet domain in order to accurately detect the borders around the prostate. The prostate contour is then traced by using a set of spatially variant rules that are based on prior knowledge about the general shape of the prostate. The proposed method yielded promising results when applied to real data.

Short echo time in vivo prostate 1H-MRSI

Visualization of short echo time (TE) metabolites in prostate magnetic resonance spectroscopic imaging is difficult due to lipid contamination and pulse timing constraints. In this work, we present a modified pulse sequence to permit short echo time (TE=40ms) acquisitions with reduced lipid contamination for the detection of short TE metabolites. The modified pulse sequence employs the conformal voxel MRS (CV-MRS) technique, which automatically optimizes the placement of spatial saturation planes to adapt the excitation volume to the shape of the prostate, thus reducing lipid contamination in prostate magnetic resonance spectroscopic imaging (MRSI). Metabolites were measured and assessed using a modified version of LCModel for analysis of in vivo prostate spectra. We demonstrate the feasibility of acquiring high quality spectra at short TEs, and show the measurement of short TE metabolites, myo-inositol, scyllo-inositol, taurine and glutamine/glutamate for both single and multi-voxel acquisitions. In single voxels experiments, the reduction in TE resulted in 57% improvement in the signal-to-noise ratio (SNR). Additional 3D MRSI experiments comparing short (TE=40 ms), and long (TE=130 ms) TE acquisitions revealed a 35% improvement in the number of adequately fitted metabolite peaks (775 voxels over all subjects). This resulted in a 42 ± 24% relative improvement in the number of voxels with detectable citrate that were well-fitted using LCmodel. In this study, we demonstrate that high quality prostate spectra can be obtained by reducing the TE to 40 ms to detect short T2 metabolites, while maintaining positive signal intensity of the spin-coupled citrate multiplet and managing lipid suppression.

Automatic conformal prescription of very selective saturation bands for in vivo1H-MRSI of the prostate

An important step in the implementation of three‐dimensional in vivo proton magnetic resonance spectroscopic imaging (1H‐MRSI) of the prostate is the placement of spatial saturation pulses around the region of interest (ROI) for the removal of unwanted contaminating signals from peripheral tissue. The present study demonstrates the use of a technique called conformal voxel magnetic resonance spectroscopy (CV‐MRS). This method automates the placement, orientation, timing and flip angle of very selective saturation (VSS) pulses around an irregularly‐shaped, user‐defined ROI. The method employs a user adjustable number of automatically positioned VSS pulses (20 used in the present study) which null the signal from periprostatic lipids while closely conforming the shape of the excitation voxel to the shape of the prostate. A standard endorectal coil in combination with a torso‐phased array coil was used for all in vivo prostate studies. Three‐dimensional in vivo prostate 1H‐MRSI data were obtained using the proposed semi‐automated CV‐MRS technique, and compared with a standard point resolved spectroscopy (PRESS) technique at TE = 130 ms using manual placement of saturation pulses. The in vivo prostate 1H‐MRSI data collected from 12 healthy subjects using the CV‐MRS method showed significantly reduced lipid contamination throughout the prostate, and reduced baseline distortions. On average there was a 50 ± 17% (range 12% – 68%) reduction in lipids throughout the prostate. A voxel‐by‐voxel benchmark test of over 850 voxels showed that there were 63% more peaks fitted using the LCModel when using a Cramer‐Rao Lower Bound (CRLB) cut‐off of 40% when using the optimized conformal voxel technique in comparison to the manual placement approach. The evaluation of this CV‐MRS technique has demonstrated the potential for easy automation of the graphical prescription of saturation bands for use in 1H‐MRSI. Copyright

Real time MRI prostate segmentation based on wavelet multiscale products flow tracking

Currently, prostate cancer is the third leading cause of cancer-related deaths among men in North America. As with many others types of cancer, early detection and treatment greatly increases the patients chance of survival. Combined Magnetic Resonance Imaging and Spectroscopic Imaging (MRI/MRSI) techniques have became a reliable tool for early stage prostate cancer detection. Nevertheless, their performance is strongly affected by the determination of the region of interest (ROI) prior to data acquisition process. The process of executing prostate MRI/MRSI techniques can be significantly enhanced by segmenting the whole prostate. A novel method for segmentation of the prostate in MRI datasets is presented. This method exploits the different behavior presented by signal singularities and noise in the wavelet domain in order to accurately detect the borders around the prostate. The prostate contour is then traced by using a set of spatially variant rules that are based on prior knowledge about the general shape of the prostate. The proposed method yielded promising results when applied to clinical datasets.

TU‐C‐330A‐05: Optimization of Outer Volume Suppression for Improved Prostate MR Spectroscopic Imaging

Purpose: To adapt a new MR Spectroscopy (MRS) technique employing non‐cuboidal voxels, called conformal voxel MRS (CV‐MRS), for use in prostate spectroscopicimaging in order to reduce contamination of spectra by lipid signal surrounding the prostate. Method and Materials: CV‐MRS uses twenty or more spatial saturation (SS) pulses, placed around the prostate, to reduce the lipid signal affecting the spectra within the prostate. A water/oil phantom was designed to simulate the prostate and surrounding lipid signal. Use of the new CV‐MRS technique reduced the lipid signal contamination by 84% as compared to standard cuboidal voxel MRS. To further reduce the lipid contamination, the routinely used 90 degree flip angle used for each SS pulse was modified to take into account the regrowth of lipid signal with its short T1relaxation time.Results: Contrary to our expectations, resulting spectra from the optimized approach actually showed an increase in lipid contamination by 10%. We tracked the problem down to overlapping SS pulses. Using a simulated 3D model, we found that 68% of the volume we were trying to saturate experienced multiple overlapping SS pulses, with some regions being saturated 7 or more times. Regions of the volume experiencing an even number of SS pulses were found to increase the lipid contamination signal by 88% to 200%. Conversely, regions experiencing an odd number of SS pulses had a reduction in lipid contamination of 55%. Conclusion: Changing the ordering of the SS pulses, such that the overlapping pulses occur later in the train of 20 SS pulses reduced the problem of lipid signal from those overlapping volumes. In summary, we have developed an improved outer volume saturation technique which reduces lipid contamination problems in prostate MR spectroscopicimaging.

SU‐GG‐BRC‐10: Shape Matters: Utilization of a Conformal Voxel Technique to Acquire Robust in Vivo Prostate MRSI at Short Echo Times

Purpose: We seek to improve the quality of in vivo prostate MRSIdata acquisition by utilizing an optimized conformal voxel technique coupled with a spatial‐spectral excitation PRESS pulse sequence for short echo time acquisitions. Method and Materials: All subjects were scanned on a GE 1.5T Signa MR scanner equipped with Echospeed gradients. A standard endorectal coil in combination with a torso phased‐array coil was used. The PRESS pulse sequence was modified to include the optimized conformal voxel MR spectroscopic imaging technique (CV‐MRS). This method uses up to twenty Very Selective Saturation (VSS) pulses, automatically positioned in three dimensions, to “conform” the excitation volume to the shape of the prostate, effectively nulling signal from periprostatic lipids. Subjects were scanned using both the standard PRESS and the optimized CV‐MRS techniques at long and short echo times (TE). In vivo prostate spectra were collected and processed using a modified version of LCModel. Results: We observed an average lipid reduction of 60±18% for 17 subjects over the entire prostate when using the optimized CV‐MRS technique as compared to standard MRSI techniques. In specific regions along the peripheral zone, we observed lipid reduction greater than 95%. The effect of reducing the lipid contamination has resulted in a ∼70% improvement in peak identification of key prostate metabolites, based on goodness‐of‐fit parameters. Furthermore, short TE acquisitions have resulted in a substantial increase in the citrate signal, full visualization of the citrate multiplet and other metabolites not seen at long echo times. Conclusion: In vivo implementation of this optimized MRSI technique has confirmed the reduction in peripheral lipid contamination, and improved the quality of spectra throughout the prostate. Furthermore, this is the first demonstration of short TE in vivo prostate MRSI acquisitions, which provides significant signal increase and reveal short TE metabolites to potentially improve prostate cancer detection.

Poster - 05: Automated analysis of MR distortion using a novel anthropomorphic phantom and open source software

Purpose: MRI in stereotactic radiosurgery is the primary imaging modality, but due to inherent distorting effects MR images have significant geometric distortions. In this work we present framework to calculate, visualize, track MRI distortion using a combination of open source tools, and in-house software on a novel anthropomorphic head phantom. Methods: The phantom used in this study was an anthropomorphic skull containing a 3D orthogonal grid of rods whose intersections are used as principle points for CT and MR image comparison. High resolution CT images were taken of the phantom. MRI images of the phantom were obtained on our 3T MRI system using a three-dimensional T1 weighted sequence. MRI data was collected with and without using Siemens model based 3D distortion correction method. MRI images were automatically rigidly registered to the CT images. For comparison, images were automatically rigidly registered using the Velocity software. The same process was repeated using deformable imaging methods. A point-by-point comparison of the centroids generates a distortion map which can be applied to subsequent patient MR images. This distortion map is compared to a baseline value and monitored over time using an open source tracking software. Results and Conclusions: We have developed in-house software to identify principle points within the phantom using CT imaging to a high spacing accuracy. With the current implemented imaging optimization, this open source software framework has promise in creating accurate distortion maps, and and thus could be used in a stereotactic radiosurgery setting for routine quality assurance.

TH-C-L100J-05: In Vivo Prostate MRSI Using An Improved Outer Volume Suppression Technique

Purpose: To implement, in vivo, an optimized prostate 3D MR SpectroscopyImaging(MRSI) technique which improves outer volume suppression of peripheral lipid and reduces lipid contamination of prostate spectroscopicimaging.Method and Materials: All scans were performed on a General Electric 1.5T Signa MR scanner equipped with Echospeed gradients. A standard quadrature head coil was used for all phantom experiments and an endorectal coil (Medrad Inc.) in combination with a torso phased arraycoil was used for all human experiments. A water/oil phantom was designed to simulate the prostate and surrounding lipid signal. The product spectroscopy pulse sequence was modified to include twenty or more optimized spatial saturation pulses. 3D MRSI spectra, employing the optimized prostate spectroscopy technique, was collected from both phantom and in vivo prostate. Results: Phantom results obtained using a standard 3D MRSI technique, which uses 4 manually placed spatial saturation pulses, showed significant lipid contamination well within the object where lipid is not present. Using the optimized spectroscopic technique on the prostate phantom we observed a 80% reduction in peripheral lipid. The 3D MRSI spectra revealed that significant reduction within all parts of the phantom were observed. Consistent with our phantom experiments, initial in vivo 3D MRSI of the prostate demonstrates, in some voxels, up to 100% reduction of lipid contamination due to peripheral contamination. Conclusion: Phantom results indicate that significant lipid contamination occurs when using manually placed spatial saturation pulses. Using this novel, optimized MRSI technique has significantly reduced the problem related to lipid contamination. In vivo, implementation of the optimized MRSI technique has confirmed the decrease in peripheral lipid contamination. Thus a technique has been established which reduces the negative effect of perisprostatic lipid in prostate spectroscopy.