Magnitude Subtraction Research Articles

Highly accelerated subtractive femoral non-contrast-enhanced MRA using compressed sensing with k-space subtraction, phase and intensity correction.

To develop an improved reconstruction method, k-space subtraction with phase and intensity correction (KSPIC), for highly accelerated, subtractive, non-contrast-enhanced MRA. The KSPIC method is based on k-space subtraction of complex raw data. It applies a phase-correction procedure to restore the polarity of negative signals caused by subtraction and an intensity-correction procedure to improve background suppression and thereby sparsity. Ten retrospectively undersampled data sets and 10 groups of prospectively undersampled data sets were acquired in 12 healthy volunteers. The performance of KSPIC was compared with another improved reconstruction based on combined magnitude subtraction, as well as with conventional k-space subtraction reconstruction and magnitude subtraction reconstruction, both using quantitative metrics and using subjective quality scoring. In the quantitative evaluation, KSPIC had the best performance in terms of peak SNR, structural similarity index measure, contrast-to-noise ratio of artery-to-background and sharpness, especially at high acceleration factors. The KSPIC method also had the highest subjective scores for all acceleration factors in terms of vessel delineation, image noise and artifact, and background contamination. The acquisition can be accelerated by a factor of 20 without significant decreases of subjective scores. The optimal size of the phase-correction region was found to be 12-20 pixels in this study. Compared with combined magnitude subtraction and conventional reconstructions, KSPIC has the best performance in all of the quantitative and qualitative measurements, permitting good image quality to be maintained up to higher accelerations. The KSPIC method has the potential to further reduce the acquisition time of subtractive MRA forclinicalexaminations.

Improved volumetric myelin imaging in human brain using 3D dual echo inversion recovery-prepared UTE with complex echo subtraction.

Inversion recovery-based UTE (IR-UTE) sequences have been proposed to directly image myelin with extremely short (~0.3 ms). In this study, we demonstrate the feasibility of complex echo subtraction to improve 3D IR-UTE imaging of myelin in white matter of the brain in vivo. In IR-UTE imaging, long T2 components in white matter (i.e., water) are suppressed using an adiabatic inversion recovery preparation pulse. Dual echo UTE data acquisition and magnitude echo subtraction are used to suppress the residual white matter and gray matter signals, providing high myelin contrast. Complex echo subtraction may further improve the myelin contrast byreducing the residual long T2 water signal contamination caused by regional T1 variations. To verify the efficacy of the complex subtraction technique, in vivo experiments were performed with 5 non-symptomatic healthy volunteers and 5 multiple sclerosis patients on a 3T clinical MR system. Signal enhancement between the complex subtraction and the magnitude subtraction was introduced to evaluate the improvement. The complex subtraction improved myelin contrast over the magnitude subtraction in both healthy and patient groups, with more fine myelin structures being revealed. The foci of the demyelinated lesion were more clearly detected by complex subtraction. An average signal enhancement of up to 135.9% was achieved with the complex subtraction over the magnitude subtraction. The complex echo subtraction improves 3D IR-UTE morphologic imaging of myelin in white matter of the brain.

Accelerated noncontrast-enhanced 4-dimensional intracranial MR angiography using golden-angle stack-of-stars trajectory and compressed sensing with magnitude subtraction.

To evaluate the feasibility and performance of compressed sensing (CS) with magnitude subtraction regularization in accelerating non-contrast-enhanced dynamic intracranial MR angiography (NCE-dMRA). A CS algorithm was introduced in NCE-dMRA by exploiting the sparsity of the magnitude difference of the control and label images. The NCE-dMRA data were acquired using golden-angle stack-of-stars trajectory on six healthy volunteers and one patient with arteriovenous fistula. Images were reconstructed using (i) the proposed magnitude-subtraction CS (MS-CS); (ii) complex-subtraction CS; (iii) independent CS; and (iv) view-sharing with k-space weighted image contrast (KWIC). The dMRA image quality was compared across the four reconstruction strategies. The proposed MS-CS method was further compared with KWIC for temporal fidelity of depicting dynamic flow. The proposed MS-CS method was able to reconstruct NCE-dMRA images with detailed vascular structures and clean background. It provided better subjective image quality than the other two CS strategies (P < 0.05). Compared with KWIC, MS-CS showed similar image quality, but reduced temporal blurring in delineating the fine distal arteries. The MS-CS method is a promising CS technique for accelerating NCE-dMRA acquisition without compromising image quality and temporal fidelity. Magn Reson Med 79:867-878, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Noninvasive assessment of perfusion in virus-associated VX2 tumors using MR spin labeling technique

The purpose of this study was to evaluate an MR arterial spin-labeling technique to characterize regions of hyper- and hypovascularity in virus-associated rabbit VX2 tumors. Shope papillomavirus-associated VX2 carcinoma cells were implanted bilaterally in the thigh musculature of 17 New Zealand White rabbits. MR imaging sequences included a T2-weighted sequence and the arterial spin-labeling technique, flow-sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER). Areas of viable and non-viable tumor were estimated based on the spin echo imaging sequences. Perfusion images were obtained from a magnitude subtraction of the labeled from the unlabeled images from the FAIRER sequence. Region of interest (ROI) analysis was performed in muscle, viable tumor regions, and necrotic tumor regions. Mean ROI signal intensities for viable tumor vs. muscle and necrotic tumor vs. muscle were compared using the student t-test. Spin echo imaging demonstrated tumors in 30 of 34 thighs. Perfusion images were successfully obtained in all cases. Mean ROIs were significantly greater in regions of viable tumor compared to those in muscle (p < 0.001). Mean ROIs were significantly less in regions of necrotic tumor compared to those in muscle (p < 0.001). Virus-associated VX2 tumors serve a good model for evaluating arterial spin labeling technique. This technique may be valuable in diagnosing hypervascular areas of tumors that would be amenable to preoperative embolization, such as intracranial meningiomas.

2-D Speech Enhancement based on Curvelet Transform using Different Window Functions

In this paper, an improved method based on Curvelet Transform using different window functions is presented for the speech enhancement. The window function is used for preprocessing of speech signals. In this method, instead of using two-dimensional (2-D) discrete Fourier Transform, Curvelet transform is employed with spectral magnitude subtraction method. General terms Spectral Substraction Method, Curvlet transform.

High spatial and temporal resolution dynamic contrast-enhanced magnetic resonance angiography using compressed sensing with magnitude image subtraction

We propose a compressed-sensing (CS) technique based on magnitude image subtraction for high spatial and temporal resolution dynamic contrast-enhanced MR angiography (CE-MRA). Our technique integrates the magnitude difference image into the CS reconstruction to promote subtraction sparsity. Fully sampled Cartesian 3D CE-MRA datasets from 6 volunteers were retrospectively under-sampled and three reconstruction strategies were evaluated: k-space subtraction CS, independent CS, and magnitude subtraction CS. The techniques were compared in image quality (vessel delineation, image artifacts, and noise) and image reconstruction error. Our CS technique was further tested on seven volunteers using a prospectively under-sampled CE-MRA sequence. Compared with k-space subtraction and independent CS, our magnitude subtraction CS provides significantly better vessel delineation and less noise at 4× acceleration, and significantly less reconstruction error at 4× and 8× (P < 0.05 for all). On a 1-4 point image quality scale in vessel delineation, our technique scored 3.8 ± 0.4 at 4×, 2.8 ± 0.4 at 8×, and 2.3 ± 0.6 at 12× acceleration. Using our CS sequence at 12× acceleration, we were able to acquire dynamic CE-MRA with higher spatial and temporal resolution than current clinical TWIST protocol while maintaining comparable image quality (2.8 ± 0.5 vs. 3.0 ± 0.4, P = NS). Our technique is promising for dynamic CE-MRA.

SU‐E‐J‐31: MR Only Simulation for Radiation Therapy _ DRR Generation

Purpose: MRI only radiation therapy has been increasingly gaining research interests. Conventionally, MRIs are fused with CT to take advantage of its superior soft tissue contrast. Such an approach has drawbacks such as additional uncertainty from fusion and extra cost. To achieve MR‐based simulation for radiation therapy, bone imaging is an important challenge that needs to be overcome. The ultra‐short T2 and T1 of cortical bone Result in low signal intensity, which presents difficulty for both dose calculation and patient setup in terms of digitally reconstructed radiograph (DRR) generation. Current solutions will either require manual bone contouring or multiple MR scans. We present a technique to generate brain DRR using bone MRI with a single Ultra Short Echo Time (UTE) sequence. Methods: Healthy volunteers were scanned at 1.5 Tesla using a radial UTE sequence. The sequence acquires two images at two different echo times (0.07ms and 3.6ms). The two images were processed using in‐house software, which performs pixel‐by‐pixel magnitude subtraction of the two images. The difference image was subsequently divided pixel‐by‐pixel to the long TE (3.6ms) image. As the cortical bone has larger percentile difference between the UTE and long TE image compared with other tissues, the bone is bright in the processed image. The resultant bone images were subsequently loaded into commercial treatment planning system to generate DRRs. Results: The majority of cranial, facial and vertebral bones are well visualized in both volunteers. The fused image of the long TE image with the processed bone image demonstrates the accuracy of automatic bone identification using our technique. The generated DRR is of acceptable quality. Conclusion: This study shows the potential of DRR generation with single MR sequence. Further work will be needed on MR sequence development and post‐processing procedure to achieve MR bone image with comparable quality to CT.

Detection of image differences by Fourier transformed magnitude subtraction

We propose a method for high-speed and highly accurate detection of the image difference by using the Fourier spectrum magnitude difference. The difference can be extracted from subtraction between the Fourier spectrum magnitude images of a standard image and a target image, which are multiplied by their Fourier spectrum phase images. The size effect against the detection result of difference was also investigated.

Highly accelerated contrast-enhanced MR angiography: Improved reconstruction accuracy and reduced noise amplification with complex subtraction

Contrast-enhanced magnetic resonance angiography is routinely performed using parallel imaging to best capture the first pass of contrast material through the target vasculature, followed by digital subtraction to suppress the appearance of unwanted signal from background tissue. Both processes, however, amplify noise and can produce uninterpretable images when large acceleration factors are used. Using a phantom study of contrast-enhanced magnetic resonance angiography, we show that complex subtraction processing prior to partially parallel reconstruction improves reconstruction accuracy relative to magnitude subtraction processing for reduction factors as large as 12. Time-resolved contrast-enhanced magnetic resonance angiographic data obtained with complex subtraction in volunteers supported the results of the phantom study and when compared with magnitude subtraction processing demonstrated reduced geometry factors as well as improved image quality at large reduction factors.

3D noncontrast MR angiography of the distal lower extremities using flow‐sensitive dephasing (FSD)‐prepared balanced SSFP

While three-dimensional contrast-enhanced MR angiography (MRA) is becoming the method of choice for clinical peripheral arterial disease (PAD) examinations, safety concerns with contrast administration in patients with renal insufficiency have triggered a renaissance of noncontrast MRA. In this work, a noncontrast-MRA technique using electrocardiography-triggered three-dimensional segmented balanced steady-state free precession with flow-sensitive dephasing (FSD) magnetization preparation was developed and tested in the distal lower extremities. FSD preparation was used to induce arterial flow voids at systolic cardiac phase while having little effect on venous blood and static tissues. High-spatial-resolution MRA was obtained by means of magnitude subtraction between a dark-artery scan with FSD preparation at systole and a bright-artery scan without FSD preparation at mid-diastole. In nine healthy volunteers, FSD parameters, including the gradient waveform and the first-order gradient moment, were optimized for excellent MRA image quality. Furthermore, arterial stenosis and occlusion in two peripheral arterial disease patients were identified using the noncontrast-MRA technique, as confirmed by contrast-enhanced MRA. In conclusion, FSD-prepared balanced steady-state free precession in conjunction with electrocardiography gating and image subtraction provides a promising noncontrast-MRA strategy for the distal lower extremities.

Cerebral venography using fluid-suppressed STARFIRE

Fluid-suppressed STARFIRE (Signal Targeting Alternative Radiofrequency and Flow-Independent Relaxation Enhancement) is a noncontrast method for flow-independent MR venography (MRV). It uses magnitude subtraction of two inversion recovery-prepared segmented three-dimensional (3D) balanced steady-state free precession acquisitions to obtain isotropic cerebral venograms in which both fat and cerebrospinal fluid signals are suppressed. Unlike two-dimensional time-of-flight (2D TOF) MRV, it is insensitive to the flow velocity of the cerebral veins. The method provided excellent depiction of the dural venous sinuses and cortical veins on maximum intensity projection images. Fluid-suppressed STARFIRE and 2D TOF were compared with contrast-enhanced 3D MRV as the reference standard in seven healthy subjects at 1.5 Tesla. Fluid-suppressed STARFIRE compared favorably to 2D TOF on both quantitative and qualitative analyses. Contrast-enhanced MRV provided the highest vein-background relative contrast and best demonstrated the straight sinus, whereas STARFIRE depicted the most venous branches. Further investigation will be required to determine the accuracy for cerebral venous thrombosis.

Subtraction of in‐phase and opposed‐phase images in dynamic MR mammography

To develop and to evaluate an advanced image acquisition and analysis method for collecting T(1)-weighted dynamic 3D MR mammography data sets by using a combined in-phase (IP) and opposed-phase (OP) imaging procedure. 3D MR mammography data sets were acquired by applying an interleaved gradient-echo OP and IP imaging sequence during administration of contrast agent. A phantom data set, two volunteer breast data sets, and six patient breast data sets were recorded. Subtraction of dynamic in-phase magnitude images was performed for clinical assessment. In addition, the magnitude subtraction (SIPOP) as well as the complex subtraction (cSIPOP) of the IP and OP magnitude and phase images were considered. The detection of small lesions, lesion boundaries, and tumor offshoots in fatty tissue was improved by the subtraction of IP and OP images without the risk of signal cancellation due to partial volume effects. Dynamic MR mammography acquisition of IP and OP images in combination with appropriate data processing yields important supplementary information that can support routinely applied diagnostics of breast lesions that are fully embedded in fatty tissue by only marginally increasing acquisition time.

Selective magnitude subtraction for noise reduction

A new method of spectral subtraction is proposed in this paper. Through selective application of common spectral magnitude subtraction, distortion in the processed speech can be reduced significantly without compromising on the amount of residual noise. The decision for the selection can be obtained from the noisy speech itself. A scheme for reducing the amount of residual noise as well as its musical nature is also included. The proposed algorithm is tested on both white noise and F16 noise with highly favorable results.