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1.
Magn Reson Med ; 2024 Sep 25.
Article in English | MEDLINE | ID: mdl-39322985

ABSTRACT

PURPOSE: To study if adaptive image receive (AIR) receiver coil elements can be configured into a 2D array with high (>45% by diameter) element-to-element overlap, allowing improved SNR at depth (0.7-1.5× element diameter) versus conventional (20%) overlap. METHODS: An anterior array composed of twenty 10-cm diameter elements with 45% overlap arranged into a 4 × 5 grid and a similar 3 × 7 twenty-one-element posterior array were constructed. SNR and g-factor were measured in a pelvic phantom using the new high-density (HD) arrays (41 total elements) and compared to vendor AIR-based arrays (30 total elements) with conventional overlap. T2-weighted fast-spin-echo (T2SE) images acquired using both arrays were compared in 20 subjects. SNR was estimated in vivo. Results were compared blindly by three uroradiologists using a five-point scale. Images using the HD arrays were also compared to a set of images acquired over a range of acceleration factors (R = 2.0, 2.5, 3.0) with the conventional arrays. RESULTS: SNR within the phantom was on average 15% higher for R = 1.0, 1.5, and 2.0 using the HD arrays. Across the 20 subjects SNR within the prostate was 11% higher and assessed radiologically as significantly higher (p < 0.001) for the HD versus conventional arrays. At all acceleration factors the new HD arrays outperformed the conventional arrays (p ≤ 0.01), allowing increased R for similar SNR. CONCLUSION: AIR elements can be configured into 2D arrays with high (45%) element-to-element overlap, consistently providing increased SNR at depth versus arrays with conventional (20%) overlap. The SNR improvement allows increased acceleration in T2SE prostate MRI.

2.
Magn Reson Med ; 89(1): 454-468, 2023 Jan.
Article in English | MEDLINE | ID: mdl-36093998

ABSTRACT

PURPOSE: The purpose is to develop a model-based image-reconstruction method using wavelet sparsity regularization for maintaining restoration of through-plane resolution but with improved retention of SNR versus linear reconstruction using Tikhonov (TK) regularization in high through-plane resolution (1 mm) T2 -weighted spin-echo (T2SE) images of the prostate. METHODS: A wavelet sparsity (WS)-regularized image reconstruction was developed that takes as input a set of ≈80 overlapped 3-mm-thick slices acquired using a T2SE multislice scan and typically 30 coil elements. After testing in contrast and resolution phantoms and calibration in 6 subjects, the WS reconstruction was evaluated in 16 consecutive prostate T2SE MRI exams. Results reconstructed with nominal 1-mm thickness were compared with those from the TK reconstruction with the same raw data. Results were evaluated radiologically. The ratio of magnitude of prostate signal to periprostatic muscle signal was used to assess the presence of noise reduction. Technical performance was also compared with a commercial 3D-T2SE sequence. RESULTS: The new WS reconstruction was assessed as superior statistically to TK for overall SNR, contrast, and multiple evaluation criteria related to sharpness while retaining the high (1 mm) through-plane resolution. Wavelet sparsity tended to provide improved overall diagnostic quality versus TK, but not significantly so. In all 16 studies, the prostate-to-muscle signal ratio increased. CONCLUSIONS: Model-based WS-regularized reconstruction consistently provides improved SNR in high (1 mm) through-plane resolution images of prostate T2SE MRI versus linear reconstruction using TK regularization.


Subject(s)
Magnetic Resonance Imaging , Prostate , Male , Humans , Prostate/diagnostic imaging , Magnetic Resonance Imaging/methods , Phantoms, Imaging , Pelvis , Image Processing, Computer-Assisted/methods
3.
Magn Reson Med ; 85(3): 1350-1363, 2021 03.
Article in English | MEDLINE | ID: mdl-32970892

ABSTRACT

PURPOSE: The purpose is to develop a retrospective correction for subtle slice-to-slice positional inconsistencies that can occur when overlapped slices are acquired for super resolution in T2 -weighted spin-echo multislice imaging. METHODS: Spin-echo acquisition of overlapped slices is typically done using multiple passes. After the passes are assembled into the final slice set, consecutive slices are correlated due to their overlap. Cross correlation was used to measure slice-to-slice displacement. After Z-dependent filtering to preserve true object shape, the displacements were used to correct slice position. The method was tested in a phantom moved slowly (0.16-0.63 mm/pass) under computer control and in vivo in 16 patients having prostate MRI. RESULTS: Over the motion range, the correlation method had an accuracy within 0.03 mm/pass and precision ± 0.20 mm (ie, subpixel). Corrected images visually resemble the true object. Over the patient studies, the mean range of motion in the anterior-posterior direction was 1.63 mm. Motion-corrected axial images and the sagittal reformats were evaluated as significantly superior over those formed without motion correction. CONCLUSION: The retrospective correlation-based motion-correction method provides significant improvement in the slice-to-slice registration necessary for effective super resolution using overlapped slices.


Subject(s)
Magnetic Resonance Imaging , Prostate , Humans , Male , Motion , Phantoms, Imaging , Prostate/diagnostic imaging , Retrospective Studies
4.
Magn Reson Med ; 84(5): 2537-2550, 2020 11.
Article in English | MEDLINE | ID: mdl-32419197

ABSTRACT

PURPOSE: To reduce slice-to-slice motion effects in multislice T2 -weighted fast-spin-echo ( T2 FSE) imaging, manifest as "scalloping" in reformats, by modification of the acquisition strategy and to show applicability in prostate MRI. METHODS: T2 FSE images of contiguous or overlapping slices are typically acquired using multiple passes in which each pass is comprised of multiple slices with slice-to-slice gaps. Combination of slices from all passes provides the desired sampling. For enhancement of through-plane resolution with super resolution or for reformatting into other orientations, subtle ≈1 mm motion between passes can cause objectionable "scalloping" artifact. Here we address this by subdivision of each pass into multiple segments. Interleaving of segments from the multiple passes causes all slices to be acquired over substantially the same time, reducing pass-to-pass motion effects. This was implemented in acquiring 78 overlapped T2 FSE axial slices and studied in phantoms and in 14 prostate MRI patients. Super-resolution axial images and sagittal reformats from the original and new segmented acquisitions were evaluated by 3 uroradiologists. RESULTS: For all criteria of sagittal reformats, the segmented acquisition was statistically superior to the original. For all sharpness criteria of axial images, although the trend preferred the original acquisition, the difference was not significant. For artifact in axial images, the segmented acquisition was significantly superior. CONCLUSIONS: For prostate MRI the new segmented acquisition significantly reduces the scalloping motion artifact that can be present in reformats due to long time lags between the acquisition of adjacent or overlapped slices while retaining image sharpness in the acquired axial slices.


Subject(s)
Artifacts , Prostate , Humans , Magnetic Resonance Imaging , Male , Motion , Phantoms, Imaging , Prostate/diagnostic imaging
5.
Magn Reson Med ; 81(6): 3691-3704, 2019 06.
Article in English | MEDLINE | ID: mdl-30844092

ABSTRACT

PURPOSE: The goal of this work is to demonstrate 1 mm through-plane resolution in multislice T2SE MRI using k Z -space processing of overlapping slices and show applicability in prostate MRI. METHODS: Multiple overlapped slices are acquired and Fourier transformed in the slice-select direction. The slice profile is incorporated into a Tikhonov-regularized reconstruction. Through-plane resolution is tested in a resolution phantom. An anthropomorphic prostate phantom is used to study the SNR, and results are compared with theoretical prediction. The proposed method is tested in 16 patients indicated for clinical prostate MRI who gave written informed consent as overseen by our IRB. The "proposed" vs. "reference" multislice images are compared using multiple evaluation criteria for through-plane resolution. RESULTS: The modulation transfer function (MTF) plots of the resolution phantom show good modulation at frequency 0.5 lp/mm, demonstrating 1 mm through-plane resolution restoration. The SNR measurements experimentally match the theoretically predicted values. The radiological evaluation shows that the proposed method is superior to the reference method for five criteria of sharpness but inferior with respect to artifacts. CONCLUSIONS: In conjunction with overlapped slices a k Z -space-based reconstruction approach can be used to improve through-plane resolution in multislice T2SE MRI. 1 mm resolution is demonstrated from 3.2 mm thick slices. The in vivo results from prostate MRI show improved sharpness when compared to the standard multislice method.


Subject(s)
Image Interpretation, Computer-Assisted/methods , Magnetic Resonance Imaging/methods , Prostate/diagnostic imaging , Aged , Humans , Male , Middle Aged , Phantoms, Imaging , Prostatic Neoplasms/diagnostic imaging
6.
Magn Reson Med ; 73(6): 2234-42, 2015 Jun.
Article in English | MEDLINE | ID: mdl-25046590

ABSTRACT

PURPOSE: To develop and validate a method for choosing the optimal two-dimensional CAIPIRINHA kernel for subtraction contrast-enhanced MR angiography (CE-MRA) and estimate the degree of image quality improvement versus that of some reference acceleration parameter set at R ≥ 8. METHODS: A metric based on patient-specific coil calibration information was defined for evaluating optimality of CAIPIRINHA kernels as applied to subtraction CE-MRA. Evaluation in retrospective studies using archived coil calibration data from abdomen, calf, foot, and hand CE-MRA exams was accomplished with an evaluation metric comparing the geometry factor (g-factor) histograms. Prospective calf, foot, and hand CE-MRA studies were evaluated with vessel signal-to-noise ratio (SNR). RESULTS: Retrospective studies show g-factor improvement for the selected CAIPIRINHA kernels was significant in the feet, moderate in the abdomen, and modest in the calves and hands. Prospective CE-MRA studies using optimal CAIPIRINHA show reduced noise amplification with identical acquisition time in studies of the feet, with minor improvements in the hands and calves. CONCLUSION: A method for selection of the optimal CAIPIRINHA kernel for high (R ≥ 8) acceleration CE-MRA exams given a specific patient and receiver array was demonstrated. CAIPIRINHA optimization appears valuable in accelerated CE-MRA of the feet and to a lesser extent in the abdomen.


Subject(s)
Foot/blood supply , Hand/blood supply , Image Enhancement/methods , Image Processing, Computer-Assisted/methods , Leg/blood supply , Magnetic Resonance Angiography/methods , Angiography, Digital Subtraction , Calibration , Contrast Media , Humans , Prospective Studies , Retrospective Studies
7.
J Magn Reson Imaging ; 42(1): 3-22, 2015 Jul.
Article in English | MEDLINE | ID: mdl-26032598

ABSTRACT

Contrast-enhanced magnetic resonance angiography (CE-MRA) was first introduced for clinical studies approximately 20 years ago. Early work provided 3-4 mm spatial resolution with acquisition times in the 30-second range. Since that time there has been continuing effort to provide improved spatial resolution with reduced acquisition time, allowing high resolution 3D time-resolved studies. The purpose of this work is to describe how this has been accomplished. Specific technical enablers have been: improved gradients allowing reduced repetition times, improved k-space sampling and reconstruction methods, parallel acquisition, particularly in two directions, and improved and higher count receiver coil arrays. These have collectively made high-resolution time-resolved studies readily available for many anatomic regions. Depending on the application, ∼1 mm isotropic resolution is now possible with frame times of several seconds. Clinical applications of time-resolved CE-MRA are briefly reviewed.


Subject(s)
Contrast Media , Data Compression/methods , Image Enhancement/methods , Image Interpretation, Computer-Assisted/methods , Imaging, Three-Dimensional/methods , Magnetic Resonance Angiography/methods , Algorithms , Animals , Humans , Pattern Recognition, Automated/methods , Reproducibility of Results , Sensitivity and Specificity , Signal Processing, Computer-Assisted
8.
Radiology ; 272(1): 241-51, 2014 Jul.
Article in English | MEDLINE | ID: mdl-24635676

ABSTRACT

PURPOSE: To determine the feasibility of using real-time fluoroscopic tracking for bolus-chase magnetic resonance (MR) angiography of peripheral vasculature to image three stations from the aortoiliac bifurcation to the pedal arteries. MATERIALS AND METHODS: This prospective study was institutional review board approved and HIPAA compliant. Eight healthy volunteers (three men; mean age, 48 years; age range, 30-81 years) and 13 patients suspected of having peripheral arterial disease (five men; mean age, 67 years; age range, 47-81 years) were enrolled and provided informed consent. All subjects were imaged with the fluoroscopic tracking MR angiographic protocol. Ten patients also underwent a clinical computed tomographic (CT) angiographic runoff examination. Two readers scored the MR angiographic studies for vessel signal intensity and sharpness and presence of confounding artifacts and venous contamination at 35 arterial segments. Mean aggregate scores were assessed. The paired MR angiographic and CT angiographic studies also were scored for visualization of disease, reader confidence, and overall diagnostic quality and were compared by using a Wilcoxon signed rank test. RESULTS: Real-time fluoroscopic tracking performed well technically in all studies. Vessel segments were scored good to excellent in all but the following categories: For vessel signal intensity and sharpness, the abdominal aorta, iliac arteries, distal plantar arteries, and plantar arch were scored as fair to good; and for presence of confounding artifacts, the abdominal aorta and iliac arteries were scored as fair. The MR angiograms and CT angiograms did not differ significantly in any scoring category (reader 1: P = .50, .39, and .39; reader 2: P = .41, .61, and .33, respectively). CT scores were substantially better in 20% (four of 20) and 25% (five of 20) of the pooled evaluations for the visualization of disease and overall image quality categories, respectively, versus 5% (one of 20) for MR scores in both categories. CONCLUSION: Three-station bolus-chase MR angiography with real-time fluoroscopic tracking provided high-spatial-resolution arteriograms of the peripheral vasculature, enabled precise triggering of table motion, and compared well with CT angiograms.


Subject(s)
Abdomen/blood supply , Contrast Media , Imaging, Three-Dimensional , Leg/blood supply , Magnetic Resonance Angiography/methods , Peripheral Vascular Diseases/diagnosis , Adult , Aged , Feasibility Studies , Female , Fluoroscopy , Humans , Image Interpretation, Computer-Assisted , Male , Meglumine/analogs & derivatives , Middle Aged , Organometallic Compounds , Peripheral Vascular Diseases/diagnostic imaging , Tomography, X-Ray Computed
9.
Magn Reson Med ; 71(2): 672-80, 2014 Feb.
Article in English | MEDLINE | ID: mdl-23450817

ABSTRACT

PURPOSE: In 2D SENSE-accelerated 3D Cartesian acquisition, the net acceleration factor R is the product of the two individual accelerations, R = RY × RZ. Acceleration Apportionment tailors acceleration parameters (RY, RZ) to improve parallel imaging performance on a patient- and coil-specific basis and is demonstrated in contrast-enhanced MR angiography. METHODS: A performance metric is defined based on coil sensitivity information which identifies the (RY, RZ) pair that optimally trades off image quality with scan time reduction on a patient-specific basis. Acceleration Apportionment is evaluated using retrospective analysis of contrast-enhanced MR angiography studies, and prospective studies in which optimally apportioned parameters are compared with standard acceleration parameters. RESULTS: The retrospective studies show strong variability in optimal acceleration parameters between anatomic regions and between patients. Prospective application of apportionment to foot contrast-enhanced MR angiography with an 8-channel receiver array provides a 20% increase in net acceleration with improved contrast-to-noise ratio. Application to 16-channel contrast-enhanced MR angiography of the feet and calves suggests 10% acceleration increase to R > 13 and no contrast-to-noise ratio loss. The specific implementation allows the optimum (RY, RZ) pair to be determined within one minute. CONCLUSION: Optimum 2D SENSE acceleration parameters can be automatically chosen on a per-exam basis to allow improved performance without disrupting the clinical workflow.


Subject(s)
Arteries/anatomy & histology , Image Enhancement/methods , Imaging, Three-Dimensional/methods , Magnetic Resonance Angiography/methods , Magnetic Resonance Imaging/methods , Meglumine/analogs & derivatives , Organometallic Compounds , Algorithms , Contrast Media , Humans , Image Interpretation, Computer-Assisted/methods , Reproducibility of Results , Sensitivity and Specificity , Signal Processing, Computer-Assisted
10.
J Magn Reson Imaging ; 39(5): 1161-70, 2014 May.
Article in English | MEDLINE | ID: mdl-23897776

ABSTRACT

PURPOSE: To describe and evaluate the method we refer to as "vascular masking" for improving signal-to-noise ratio (SNR) retention in sensitivity encoding (SENSE)-accelerated contrast-enhanced magnetic resonance angiography (CE-MRA). MATERIALS AND METHODS: Vascular masking is a technique that restricts the SENSE unfolding of an accelerated subtraction angiogram to the voxels within the field of view known to have enhancing signal. This is a more restricted voxel set than that identified with conventional masking, which excludes only voxels in the air around the object. Thus, improved retention of SNR is expected. Evaluation was done in phantom and in vivo studies by comparing SNR and the g-factor in results reconstructed using vascular versus conventional masking. A radiological evaluation was also performed comparing conventional and vascular masking in R = 8 accelerated CE-MRA studies of the thighs (n = 21) and calves (n = 13). RESULTS: Images reconstructed with vascular masking showed a significant reduction in g-factor and improved retention of SNR versus those reconstructed with conventional masking. In the radiological evaluation, vascular masking consistently provided reduced background noise, improved luminal signal smoothness, and better small vessel conspicuity. CONCLUSION: Vascular masking provides improved SNR retention and improved depiction of the vasculature in accelerated, subtraction 3D CE-MRA of the thighs and calves.


Subject(s)
Femoral Artery/anatomy & histology , Gadolinium , Image Enhancement/methods , Imaging, Three-Dimensional/methods , Magnetic Resonance Angiography/methods , Subtraction Technique , Tibial Arteries/anatomy & histology , Algorithms , Contrast Media , Female , Humans , Image Interpretation, Computer-Assisted/methods , Male , Middle Aged , Observer Variation , Reproducibility of Results , Sensitivity and Specificity
11.
Abdom Radiol (NY) ; 49(8): 2921-2931, 2024 Aug.
Article in English | MEDLINE | ID: mdl-38520510

ABSTRACT

PURPOSE: To compare a previous model-based image reconstruction (MBIR) with a newly developed deep learning (DL)-based image reconstruction for providing improved signal-to-noise ratio (SNR) in high through-plane resolution (1 mm) T2-weighted spin-echo (T2SE) prostate MRI. METHODS: Large-area contrast and high-contrast spatial resolution of the reconstruction methods were assessed quantitatively in experimental phantom studies. The methods were next evaluated radiologically in 17 subjects at 3.0 Tesla for whom prostate MRI was clinically indicated. For each subject, the axial T2SE raw data were directed to MBIR and to the DL reconstruction at three vendor-provided levels: (L)ow, (M)edium, and (H)igh. Thin-slice images from the four reconstructions were compared using evaluation criteria related to SNR, sharpness, contrast fidelity, and reviewer preference. Results were compared using the Wilcoxon signed-rank test using Bonferroni correction, and inter-reader comparisons were done using the Cohen and Krippendorf tests. RESULTS: Baseline contrast and resolution in phantom studies were equivalent for all four reconstruction pathways as desired. In vivo, all three DL levels (L, M, H) provided improved SNR versus MBIR. For virtually, all other evaluation criteria DL L and M were superior to MBIR. DL L and M were evaluated as superior to DL H in fidelity of contrast. For 44 of the 51 evaluations, the DL M reconstruction was preferred. CONCLUSION: The deep learning reconstruction method provides significant SNR improvement in thin-slice (1 mm) T2SE images of the prostate while retaining image contrast. However, if taken to too high a level (DL High), both radiological sharpness and fidelity of contrast diminish.


Subject(s)
Deep Learning , Magnetic Resonance Imaging , Phantoms, Imaging , Prostatic Neoplasms , Signal-To-Noise Ratio , Humans , Male , Magnetic Resonance Imaging/methods , Prostatic Neoplasms/diagnostic imaging , Image Interpretation, Computer-Assisted/methods , Image Processing, Computer-Assisted/methods , Prostate/diagnostic imaging , Middle Aged , Aged
12.
J Magn Reson Imaging ; 36(5): 1168-78, 2012 Nov.
Article in English | MEDLINE | ID: mdl-22753021

ABSTRACT

PURPOSE: To refine, adapt, and evaluate the technical aspects of fluoroscopic tracking for generating dual-station high-spatial-resolution MR angiograms of the calves and feet using a single injection of contrast material. MATERIALS AND METHODS: Nine subjects (seven healthy volunteers followed by two patients) were imaged using a two-station calf-foot three-dimensional time-resolved bolus chase MR angiography protocol which provided <1.0 mm(3) spatial resolution throughout and 2.5- and 6.6-s frame times at the calf and foot stations, respectively. Real-time reconstruction of calf station time frames allowed visually guided triggering of table advance to the foot station. The studies were independently read and scored by two radiologists in six image quality categories. RESULTS: On average, overall diagnostic quality at the calf and foot stations was good-to-excellent, the calf arteries and all but the smallest foot arteries had good-to-excellent signal and sharpness, artifact and venous contamination were minor, and signal continuity across the inter-station interface was good. CONCLUSION: The feasibility of fluoroscopic tracking has been demonstrated as an efficient approach for high spatiotemporal imaging of the arteries of the calves and feet with good-to-excellent diagnostic quality and low degrading venous contamination.


Subject(s)
Algorithms , Arteries/anatomy & histology , Imaging, Three-Dimensional/methods , Leg/anatomy & histology , Leg/blood supply , Magnetic Resonance Angiography/methods , Tomography, X-Ray Computed/methods , Adult , Female , Humans , Male , Middle Aged , Reproducibility of Results , Sensitivity and Specificity
13.
Magn Reson Med ; 66(4): 1019-32, 2011 Oct.
Article in English | MEDLINE | ID: mdl-21608028

ABSTRACT

Cartesian Acquisition with Projection-Reconstruction-like sampling is a SENSE-type parallel 3DFT acquisition paradigm for 4D contrast-enhanced magnetic resonance angiography that has been demonstrated capable of providing high spatial and temporal resolution, diagnostic-quality images at very high acceleration rates. However, Cartesian Acquisition with Projection-Reconstruction-like sampling images are typically reconstructed online using Tikhonov regularization and partial Fourier methods, which are prone to exhibit noise amplification and undersampling artifacts when operating at very high acceleration rates. In this work, a sparsity-driven offline reconstruction framework for Cartesian Acquisition with Projection-Reconstruction-like sampling is developed and demonstrated to consistently provide improvements over the currently-employed reconstruction strategy against these ill-effects. Moreover, the proposed reconstruction strategy requires no changes to the existing Cartesian Acquisition with Projection-Reconstruction-like sampling acquisition protocol, and an efficient numerical optimization and hardware system are described that allow for a 256 × 160 × 80 volume contrast-enhanced magnetic resonance angiography volume to be reconstructed from an eight-channel data set in less than 2 min.


Subject(s)
Cerebrovascular Circulation , Foot/blood supply , Hand/blood supply , Magnetic Resonance Angiography/methods , Algorithms , Artifacts , Child , Contrast Media , Humans , Image Enhancement/methods , Image Processing, Computer-Assisted/methods , Meglumine/analogs & derivatives , Organometallic Compounds
14.
J Magn Reson Imaging ; 34(1): 2-12, 2011 Jul.
Article in English | MEDLINE | ID: mdl-21698702

ABSTRACT

Methods are described for generating 3D time-resolved contrast-enhanced magnetic resonance (MR) angiograms of the hands and feet. Given targeted spatial resolution and frame times, it is shown that acceleration of about one order of magnitude or more is necessary. This is obtained by a combination of 2D sensitivity encoding (SENSE) and homodyne (HD) acceleration methods. Image update times from 3.4-6.8 seconds are provided in conjunction with view sharing. Modular receiver coil arrays are described which can be designed to the targeted vascular region. Images representative of the technique are generated in the vasculature of the hands and feet in volunteers and in patient studies.


Subject(s)
Angiography/methods , Contrast Media/pharmacology , Foot/pathology , Hand/pathology , Imaging, Three-Dimensional/methods , Magnetic Resonance Imaging/methods , Acceleration , Algorithms , Foot/diagnostic imaging , Hand/diagnostic imaging , Humans , Image Processing, Computer-Assisted/methods , Raynaud Disease/pathology , Time Factors
15.
Magn Reson Med ; 64(3): 629-37, 2010 Sep.
Article in English | MEDLINE | ID: mdl-20597121

ABSTRACT

Time-resolved bolus-chase contrast-enhanced MR angiography with real-time station switching is demonstrated. The Cartesian acquisition with projection reconstruction-like sampling (CAPR) technique and high 2D sensitivity encoding (SENSE) (6x or 8x) and 2D homodyne (1.8x) accelerations were used to acquire 3D volumes with 1.0-mm isotropic spatial resolution and frame times as low as 2.5 sec in two imaging stations covering the thighs and calves. A custom real-time system was developed to reconstruct and display CAPR frames for visually guided triggering of table motion upon passage of contrast through the proximal station. The method was evaluated in seven volunteers. High-spatial-resolution arteriograms with minimal venous contamination were consistently acquired in both stations. Real-time stepping table contrast-enhanced MR angiography is a method for providing time-resolved images with high spatial resolution over an extended field-of-view.


Subject(s)
Algorithms , Contrast Media/administration & dosage , Examination Tables , Image Enhancement/methods , Image Interpretation, Computer-Assisted/methods , Magnetic Resonance Angiography/instrumentation , Magnetic Resonance Angiography/methods , Adult , Aged , Computer Systems , Female , Humans , Image Enhancement/instrumentation , Male , Middle Aged , Motion , Reproducibility of Results , Sensitivity and Specificity
16.
Magn Reson Med ; 64(4): 1171-81, 2010 Oct.
Article in English | MEDLINE | ID: mdl-20715291

ABSTRACT

High temporal and spatial resolution is desired in imaging of vascular abnormalities having short arterial-to-venous transit times. Methods that exploit temporal correlation to reduce the observed frame time demonstrate temporal blurring, obfuscating bolus dynamics. Previously, a Cartesian acquisition with projection reconstruction-like (CAPR) sampling method has been demonstrated for three-dimensional contrast-enhanced angiographic imaging of the lower legs using two-dimensional sensitivity-encoding acceleration and partial Fourier acceleration, providing 1mm isotropic resolution of the calves, with 4.9-sec frame time and 17.6-sec temporal footprint. In this work, the CAPR acquisition is further undersampled to provide a net acceleration approaching 40 by eliminating all view sharing. The tradeoff of frame time and temporal footprint in view sharing is presented and characterized in phantom experiments. It is shown that the resultant 4.9-sec acquisition time, three-dimensional images sets have sufficient spatial and temporal resolution to clearly portray arterial and venous phases of contrast passage. It is further hypothesized that these short temporal footprint sequences provide diagnostic quality images. This is tested and shown in a series of nine contrast-enhanced MR angiography patient studies performed with the new method.


Subject(s)
Arteries/physiology , Image Enhancement/methods , Image Interpretation, Computer-Assisted/methods , Imaging, Three-Dimensional/methods , Leg/physiology , Magnetic Resonance Angiography/methods , Meglumine/analogs & derivatives , Organometallic Compounds , Algorithms , Arteries/anatomy & histology , Contrast Media , Humans , Leg/blood supply , Reproducibility of Results , Sensitivity and Specificity
17.
Ultrasonics ; 107: 106163, 2020 Sep.
Article in English | MEDLINE | ID: mdl-32353739

ABSTRACT

Singular value decomposition (SVD)-based clutter filters can robustly reject the tissue clutter as compared with the conventional high pass filter-based clutter filters. However, the computational burden of SVD makes real time SVD-based clutter filtering challenging (e.g. frame rate at least 10-15 Hz with region of interest of about 4 × 4 cm2). Recently, we proposed an acceleration method based on randomized SVD (rSVD) clutter filtering and randomized spatial downsampling, which can significantly reduce the computational complexity without compromising the clutter rejection capability. However, this method has not been implemented on an ultrasound scanner and tested for its performance. In this study, we implement this acceleration method on a Verasonics scanner using a multi-core CPU architecture, and evaluate the selections of the imaging and processing parameters to enable real time micro-vessel imaging. The Blood-to-Clutter Ratio (BCR) performance was evaluated on a Verasonics machine with different settings of parameters such as block size and ensemble size. The demonstration of real time process was implemented on a 12-core CPU (downsampling factor of 12, 12-threads in this study) host computer. The processing time of the rSVD-based clutter filter was less than 30 ms and BCRs were higher than 20 dB as the block size, ensemble size and the rank of tissue clutter subspace were set as 30 × 30, 45 and 26 respectively. We also demonstrate that the micro-vessel imaging frame rate of the proposed architecture can reach approximately 22 Hz when the block size, ensemble size and the rank of tissue clutter subspace were set as 20 × 20 pixels, 45 and 26 respectively (using both images and supplementary videos). The proposed method may be important for real time 2D scanning of tumor microvessels in 3D to select and store the most representative 2D view with most abnormal micro-vessels for better diagnosis.


Subject(s)
Blood Vessels/diagnostic imaging , Image Processing, Computer-Assisted/methods , Ultrasonography, Doppler/methods , Blood Flow Velocity , Computer Simulation , Phantoms, Imaging , Ultrasonography, Doppler/instrumentation
18.
Radiology ; 253(2): 532-42, 2009 Nov.
Article in English | MEDLINE | ID: mdl-19789236

ABSTRACT

This study was HIPAA compliant and institutional review board approved, and informed consent was obtained from all volunteers. The authors describe a method for generating a time-of-arrival (TOA) map of intravenously administered contrast material, as observed in a time series of three-dimensional (3D) contrast material-enhanced magnetic resonance (MR) angiograms. The method may enable visualization and interpretation, on one 3D image, of the temporal enhancement patterns that occur in the vasculature. Colorization of TOA values may further aid interpretation. The quality of the results depends not only on the adequacy of the frame rate, spatial resolution, and signal-to-noise ratio of the MR image acquisition method but also on the accuracy and clarity with which the leading edge of the contrast material bolus is depicted. The criteria for optimizing these parameters are described. The TOA mapping technique is demonstrated by using vascular studies of the hands, brain, and lower leg regions.


Subject(s)
Contrast Media/administration & dosage , Image Processing, Computer-Assisted , Imaging, Three-Dimensional , Magnetic Resonance Angiography/methods , Algorithms , Brain/blood supply , Hand/blood supply , Humans , Injections, Intravenous , Leg/blood supply
19.
Magn Reson Med ; 62(1): 85-95, 2009 Jul.
Article in English | MEDLINE | ID: mdl-19319897

ABSTRACT

Various methods have been used for time-resolved contrast-enhanced magnetic resonance angiography (CE-MRA), many involving view sharing. However, the extent to which the resultant image time series represents the actual dynamic behavior of the contrast bolus is not always clear. Although numerical simulations can be used to estimate performance, an experimental study can allow more realistic characterization. The purpose of this work was to use a computer-controlled motion phantom for study of the temporal fidelity of three-dimensional (3D) time-resolved sequences in depicting a contrast bolus. It is hypothesized that the view order of the acquisition and the selection of views in the reconstruction can affect the positional accuracy and sharpness of the leading edge of the bolus and artifactual signal preceding the edge. Phantom studies were performed using dilute gadolinium-filled vials that were moved along tabletop tracks by a computer-controlled motor. Several view orders were tested using view-sharing and Cartesian sampling. Compactness of measuring the k-space center, consistency of view ordering within each reconstruction frame, and sampling the k-space center near the end of the temporal footprint were shown to be important in accurate portrayal of the leading edge of the bolus. A number of findings were confirmed in an in vivo CE-MRA study.


Subject(s)
Algorithms , Arteries/physiology , Blood Flow Velocity/physiology , Image Enhancement/methods , Image Interpretation, Computer-Assisted/methods , Imaging, Three-Dimensional/methods , Magnetic Resonance Angiography/methods , Arteries/anatomy & histology , Contrast Media , Humans , Magnetic Resonance Angiography/instrumentation , Motion , Phantoms, Imaging , Reproducibility of Results , Rheology/methods , Sensitivity and Specificity
20.
Magn Reson Imaging ; 47: 67-76, 2018 04.
Article in English | MEDLINE | ID: mdl-29103977

ABSTRACT

PURPOSE: To evaluate if Field of view Optimized and Constrained Undistorted Single shot (FOCUS) (GE Healthcare, Waukesha, WI) diffusion weighted images (DWI) provide more reliable imaging than conventional DWI, with non-inferior quantitative apparent diffusion coefficient (ADC) results. MATERIAL AND METHODS: IRB approval was obtained for this study of 43 patients (44 exams, one patient with two visits) that underwent multiparametric prostate MRI with two DWI sequences and subsequent radical prostatectomy with histology as the gold standard. Randomized DWI sequence images were graded independently by two blinded experienced prostate MRI radiologists with a period of memory extinction between the two separate reading sessions. Blinded images were also reviewed head to head in a later session for direct comparison. Multiple parameters were measured from a region of interest in a dominant lesion as well as two control areas. Patient characteristics were collected by chart review. RESULTS: There was good correlation between the mean ADC value for lesions obtained by conventional and FOCUS DWI (ρ=0.85), with no trend toward any systematic difference, and equivalent correlation between ADC measurements and Gleason score. Agreement between the two readers was significantly higher for lesion ROI analysis with the FOCUS DWI derived ADC values (CCC 0.839) compared with the conventional ADC values (CCC 0.618; difference 0.221, 95% CI 0.01-0.46). FOCUS showed significantly better image quality scores (separate review: mean 2.17±0.6, p<0.001) compared to the conventional sequence (mean 2.65±0.6, p<0.001). In 13 cases the image quality was improved from grade of 3+ with conventional DWI to <3 with FOCUS DWI, a clinically meaningful improvement. Head-to-head blinded review found 61 ratings showed strong to slight preference for FOCUS, 13 no preference, and 14 slight preference for the conventional sequence. There was also a strong and equivalent correlation between both sequences and PIRADS version 2 grading (ρ=-0.56 and -0.58 for FOCUS and conventional, respectively, p<0.001 for both). CONCLUSION: FOCUS DWI of the prostate shows significant improvement in inter-reader agreement and image quality. As opposed to previous conflicting smaller studies, we found equivalent ADC metrics compared with the conventional DWI sequence, and preserved correlation with Gleason score. In 52% of patients the improved image quality with FOCUS had the potential to salvage exams with otherwise limited to non-diagnostic DWI.


Subject(s)
Diffusion Magnetic Resonance Imaging , Prostatic Neoplasms/diagnostic imaging , Aged , Humans , Magnetic Resonance Imaging , Male , Middle Aged , Neoplasm Grading , Observer Variation , Prostatectomy , Prostatic Neoplasms/pathology , Reproducibility of Results , Retrospective Studies
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