Evaluation of left and right ventricular systolic function by cardiac MR compressed sensing ultrafast cine sequence / 中华放射学杂志

Objective:To explore the clinical value of cardiac MR (CMR) compression sensing (CS) ultrafast cine sequence in evaluating left and right ventricular systolic function by comparing with traditional segmented acquisition cine sequence (Seg).Methods:Twenty-seven patients with various heart disease were prospectively included. Seg, breath holding CS (bhCS) and free breathing CS (fbCS) covering the left and right ventricles using multi slices in short axis were performed in random order. Friedman test was used to evaluate the overall image quality (grade 1-5 score), blood pool myocardial signal ratio (BMC) and edge sharpness under different methods. Biventricular end diastolic volume (EDV), end systolic volume (ESV), stroke volume (SV), ejection fraction (EF) and left ventricular myocardial mass (Mass) were measured for all three methods. The agreements of the functional measurements between bhCS and Seg (gold standard), and between fbCS and Seg were analyzed by Bland-Altman, and the correlation test was performed.Results:Twenty-four patients with diagnostic images(overall image quality score≥2) for all three methods were included in further analysis. The total imaging time of Seg, bhCS and fbCS decreased successively[375.0 (332.0, 405.6) vs. 50.0 (47.8, 53.7) vs. 20.0 (17.8, 23.7) s, χ 2=48.00, P<0.001]. The overall image quality of fbCS was slightly lower than that of Seg ( Z=-2.67, P=0.023), and there was no difference between Seg and bhCS ( Z=-1.44, P=0.447), bhCS and fbCS ( Z=1.23, P=0.660). There were no differences in edge sharpness (χ 2=1.08, P=0.582) and BMC (χ 2=0.58, P=0.747) for three methods. Bland-Altman polts showed good agreement for biventricular functional measurements between bhCS and Seg, and between fbCS and Seg. All functional measurements of bhCS and fbCS were highly correlated with that of seg ( r>0.96, P<0.001). Conclusions:Compared with traditional sequences, CS ultrafast cine sequences can save scanning time and provide similar image quality. No matter whether breath holding or not, the cardiac functional results of CS sequence and traditional cine sequence have good agreement and high correlation.

Clinical application of single breath-holding left ventricle artificial intelligence assisted compression sensing T 2-weighted dark blood imaging sequence / 中华放射学杂志

Objective:To explore the feasibility of cardiac T 2 weighted dark blood sequence (T 2W-DB) based on artificial intelligence assisted compression-sensing(ACS) in clinical cardiac MR examination, compared with the conventional cardiac fast spin-echo T 2W-DB sequence. Methods:A total of 38 patients referred for cardiac MR examination in Tongji Hospital were enrolled prospectively from August to December 2021. The conventional T 2W-DB scan and the single-shot ACS T 2W-DB scan were acquired at continuous short-axial slices covering the whole left ventricle in all patients, and the acquisition time of each scan was recorded. The image quality of the two sequences was evaluated by the objective quantitative parameters and the subjective scoring methods, respectively. The signal to noise ratio (SNR), the contrast to noise ratio of the interventricular septum to blood pool (CNR), and the sharpness of the images were calculated. The subjective scoring was to evaluate the overall image quality, the effect of blood pool suppression, the visibility of right ventricular free wall, left ventricular free wall, and interventricular septum with a 5-point Likert scale. The intraclass correlation coefficient and Kendall W were calculated to evaluate the interobserver agreement of the objective quantitative parameters and subjective scoring. The paired t-test or Wilcoxon test was used to compare the difference in acquisition time, objective quantitative parameters and subjective scoring between the conventional T 2W-DB and the single-shot ACS T 2W-DB. Results:The inter-observer agreement between the single-shot ACS T 2W-DB and conventional T 2W-DB was good in all the objective quantitative parameters and subjective scoring of image quality ( P<0.05 for all). Compared with conventional T 2W-DB, acquisition time of single-shot ACS T 2W-DB was remarkably shortened [(85.8±14.7) s vs. (16.9±3.0) s, t=35.42, P<0.001]. Compared with SNR (66.4±29.0) and CNR(61.8±28.6) of conventional T 2W-DB, single-shot ACS T 2W-DB had significantly higher SNR(110.8±36.8, t=-8.13, P?0.001) and CNR(88.2±31.1, t=-5.89, P?0.001). Compared with conventional T 2W-DB, single-shot ACS T 2W-DB had better blood pool inhibition effect (4.6±0.6 vs. 4.7±0.5, Z=-2.64, P=0.008). There was no significant difference in overall image quality, visibility of right ventricular free wall, left ventricular free wall, and interventricular septum between the two sequences( P>0.05 for all). Conclusions:In cardiac MR examination, compared with the conventional T 2W-DB sequence, the single-shot ACS T 2W-DB sequence can significantly shorten the acquisition time and obtain better image quality.

Three dimensional MRI based on compressed sensing technology in diagnosis of meniscal injuries / 中国医学影像技术

Objective: To investigate the feasibility of three dimensional MRI (3D-MRI) based on compressed sensing (CS) in knee joint imaging and its value in assessing meniscal injuries. Methods: Knee MRI were performed on 26 patients with suspected knee injury (injured group) and 30 healthy volunteers (control group). Conventional fat saturation proton density-weighted imaging (fsPDWI) and CS-3D-MRI were collected. The results of arthroscopy of injured group were recorded. MRI of the right knee were obtained in control group, then CS-3D-MRI were reconstructed with 3 different denosing (DS) levels (CS-DSweak, CS-DSmedium, CS-DSstrong), and the sagittal image quality was evaluated subjectively and objectively. Patients in injured group received MRI before arthroscopy. CS-3D-MRI of injured group were reconstructed with CS-DSmedium, and the consistency of CS-3D-MRI diagnostic results with those of arthroscopy was analyzed. Results: For images of control group, there was no statistical difference of the quality scores of reconstructed CS images of different DS levels and fsPDWI (Z=0.35, P=0.32), while statistically significant differences of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were found in images obtained with 4 different sequences (F=36.01, 9.62, both P0.05). CS-3D-MRI diagnosed meniscus injuries in all patients in injury group, highly consistent with results of arthroscopy (Kappa=0.94, P<0.01). Conclusion: Based on CS technique, 3D-MRI could be used for knee joint imaging, which was able to shorten scanning time on the premise of ensuring image quality, therefore had good value for evaluation on meniscus injuries.

Brain functional network reconstruction based on compressed sensing and fast iterative shrinkage-thresholding algorithm / 生物医学工程学杂志

The construction of brain functional network based on resting-state functional magnetic resonance imaging (fMRI) is an effective method to reveal the mechanism of human brain operation, but the common brain functional network generally contains a lot of noise, which leads to wrong analysis results. In this paper, the least absolute shrinkage and selection operator (LASSO) model in compressed sensing is used to reconstruct the brain functional network. This model uses the sparsity of

Advanced Methods in Dynamic Contrast Enhanced Arterial Phase Imaging of the Liver

Dynamic contrast enhanced (DCE) magnetic resonance (MR) imaging plays an important role in non-invasive detection and characterization of primary and metastatic lesions in the liver. Recently, efforts have been made to improve spatial and temporal resolution of DCE liver MRI for arterial phase imaging. Review of recent publications related to arterial phase imaging of the liver indicates that there exist primarily two approaches: breath-hold and free-breathing. For breath-hold imaging, acquiring multiple arterial phase images in a breath-hold is the preferred approach over conventional single-phase imaging. For free-breathing imaging, a combination of three-dimensional (3D) stack-of-stars golden-angle sampling and compressed sensing parallel imaging reconstruction is one of emerging techniques. Self-gating can be used to decrease respiratory motion artifact. This article introduces recent MRI technologies relevant to hepatic arterial phase imaging, including differential subsampling with Cartesian ordering (DISCO), golden-angle radial sparse parallel (GRASP), and X-D GRASP. This article also describes techniques related to dynamic 3D image reconstruction of the liver from golden-angle stack-of-stars data.

Biases in the Assessment of Left Ventricular Function by Compressed Sensing Cardiovascular Cine MRI

PURPOSE: We investigate biases in the assessments of left ventricular function (LVF), by compressed sensing (CS)-cine magnetic resonance imaging (MRI). MATERIALS AND METHODS: Cardiovascular cine images with short axis view, were obtained for 8 volunteers without CS. LVFs were assessed with subsampled data, with compression factors (CF) of 2, 3, 4, and 8. A semi-automatic segmentation program was used, for the assessment. The assessments by 3 CS methods (ITSC, FOCUSS, and view sharing (VS)), were compared to those without CS. Bland-Altman analysis and paired t-test were used, for comparison. In addition, real-time CS-cine imaging was also performed, with CF of 2, 3, 4, and 8 for the same volunteers. Assessments of LVF were similarly made, for CS data. A fixed compensation technique is suggested, to reduce the bias. RESULTS: The assessment of LVF by CS-cine, includes bias and random noise. Bias appeared much larger than random noise. Median of end-diastolic volume (EDV) with CS-cine (ITSC or FOCUSS) appeared −1.4% to −7.1% smaller, compared to that of standard cine, depending on CF from (2 to 8). End-systolic volume (ESV) appeared +1.6% to +14.3% larger, stroke volume (SV), −2.4% to −16.4% smaller, and ejection fraction (EF), −1.1% to −9.2% smaller, with P < 0.05. Bias was reduced from −5.6% to −1.8% for EF, by compensation applied to real-time CS-cine (CF = 8). CONCLUSION: Loss of temporal resolution by adopting missing data from nearby cardiac frames, causes an underestimation for EDV, and an overestimation for ESV, resulting in underestimations for SV and EF. The bias is not random. Thus it should be removed or reduced for better diagnosis. A fixed compensation is suggested, to reduce bias in the assessment of LVF.

High Acceleration Three-Dimensional T1-Weighted Dual Echo Dixon Hepatobiliary Phase Imaging Using Compressed Sensing-Sensitivity Encoding: Comparison of Image Quality and Solid Lesion Detectability with the Standard T1-Weighted Sequence

OBJECTIVE: To compare a high acceleration three-dimensional (3D) T1-weighted gradient-recalled-echo (GRE) sequence using the combined compressed sensing (CS)-sensitivity encoding (SENSE) method with a conventional 3D GRE sequence using SENSE, with respect to image quality and detectability of solid focal liver lesions (FLLs) in the hepatobiliary phase (HBP) of gadoxetic acid-enhanced liver MRI. MATERIALS AND METHODS: A total of 217 patients with gadoxetic acid-enhanced liver MRI at 3T (54 in the preliminary study and 163 in the main study) were retrospectively included. In the main study, HBP imaging was done twice using the standard mDixon-3D-GRE technique with SENSE (acceleration factor [AF]: 2.8, standard mDixon-GRE) and the high acceleration mDixon-3D GRE technique using the combined CS-SENSE technique (CS-SENSE mDixon-GRE). Two abdominal radiologists assessed the two MRI data sets for image quality in consensus. Three other abdominal radiologists independently assessed the diagnostic performance of each data set and its ability to detect solid FLLs in 117 patients with 193 solid nodules and compared them using jackknife alternative free-response receiver operating characteristics (JAFROC). RESULTS: There was no significant difference in the overall image quality. CS-SENSE mDixon-GRE showed higher image noise, but lesser motion artifact levels compared with the standard mDixon-GRE (all p < 0.05). In terms of lesion detection, reader-averaged figures-of-merit estimated with JAFROC was 0.918 for standard mDixon-GRE, and 0.953 for CS-SENSE mDixon-GRE (p = 0.142). The non-inferiority of CS-SENSE mDixon-GRE over standard mDixon-GRE was confirmed (difference: 0.064 [−0.012, 0.081]). CONCLUSION: The CS-SENSE mDixon-GRE HBP sequence provided comparable overall image quality and non-inferior solid FFL detectability compared with the standard mDixon-GRE sequence, with reduced acquisition time.

High-Resolution Magnetic Resonance Imaging Using Compressed Sensing for Intracranial and Extracranial Arteries: Comparison with Conventional Parallel Imaging

OBJECTIVE: To compare conventional sensitivity encoding (SENSE) to compressed sensing plus SENSE (CS) for high-resolution magnetic resonance imaging (HR-MRI) of intracranial and extracranial arteries. MATERIALS AND METHODS: HR-MRI was performed in 14 healthy volunteers. Three-dimensional T1-weighted imaging (T1WI) and proton density-weighted imaging (PD) were acquired using CS or SENSE under the same total acceleration factors (AF(t))-5.5, 6.8, and 9.7 for T1WI and 3.2, 4.0, and 5.8 for PD-to achieve reduced scanning times in comparison with the original imaging sequence (SENSE T1WI, AF(t) 3.5; SENSE PD, AF(t) 2.0) using the 3-tesla system. Two neuroradiologists measured signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), and used visual scoring systems to assess image quality. Acceptable imaging was defined as a visual score ≥ 2. Repeated measures analysis of variance and Cochran's Q test were performed. RESULTS: CS yielded better image quality and vessel delineation than SENSE in T1WI with AF(t) of 5.5, 6.8, and 9.7, and in PD with AF(t) of 5.8 (p 0.05). SNR and CNR in CS were higher than they were in SENSE, but lower than they were in the original images (p < 0.05). CS yielded higher proportions of acceptable imaging than SENSE (CS T1WI with AF(t) of 6.8 and PD with AF(t) of 5.8; p < 0.0167). CONCLUSION: CS is superior to SENSE, and may be a reliable acceleration method for vessel HR-MRI using AF(t) of 5.5 for T1WI, and 3.2 and 4.0 for PD.

High-quality reconstruction of four-dimensional cone beam CT from motion registration prior image / 南方医科大学学报

Four-dimensional cone beam CT (4D-CBCT) imaging can provide accurate location information of real-time breathing for imaging-guided radiotherapy. How to improve the accuracy of 4D-CBCT reconstruction image is a hot topic in current studies. PICCS algorithm performs remarkably in all 4D-CBCT reconstruction algorithms based on CS theory. The improved PICCS algorithm proposed in this paper improves the prior image on the basis of the traditional PICCS algorithm. According to the location information of each phase, the corresponding prior image is constructed, which completely eliminates the motion blur of the reconstructed image caused by the mismatch of the projection data. Meanwhile, the data fidelity model of the proposed method is consistent with the traditional PICCS algorithm. The experimental results showed that the reconstructed image using the proposed method had a clearer organization boundary compared with that of images reconstructed using the traditional PICCS algorithm. This proposed method significantly reduced the motion artifact and improved the image resolution.

High quality reconstruction algorithm for cardiac magnetic resonance images based on multiscale low rank modeling / 生物医学工程学杂志

Taking advantages of the sparsity or compressibility inherent in real world signals, compressed sensing (CS) can collect compressed data at the sampling rate much lower than that needed in Shannon's theorem. The combination of CS and low rank modeling is used to medical imaging techniques to increase the scanning speed of cardiac magnetic resonance (CMR), alleviate the patients' suffering and improve the images quality. The alternating direction method of multipliers (ADMM) algorithm is proposed for multiscale low rank matrix decomposition of CMR images. The algorithm performance is evaluated quantitatively by the peak signal to noise ratio (PSNR) and relative norm error (RLNE), with the human visual system and the local region magnification as the qualitative comparison. Compared to L + S, kt FOCUSS, k-t SPARSE SENSE algorithms, experimental results demonstrate that the proposed algorithm can achieve the best performance indices, and maintain the most detail features and edge contours. The proposed algorithm can encourage the development of fast imaging techniques, and improve the diagnoses values of CMR in clinical applications.

Rapid Imaging: Recent Advances in Abdominal MRI for Reducing Acquisition Time and Its Clinical Applications

Magnetic resonance imaging (MRI) plays an important role in abdominal imaging. The high contrast resolution offered by MRI provides better lesion detection and its capacity to provide multiparametric images facilitates lesion characterization more effectively than computed tomography. However, the relatively long acquisition time of MRI often detrimentally affects the image quality and limits its accessibility. Recent developments have addressed these drawbacks. Specifically, multiphasic acquisition of contrast-enhanced MRI, free-breathing dynamic MRI using compressed sensing technique, simultaneous multi-slice acquisition for diffusion-weighted imaging, and breath-hold three-dimensional magnetic resonance cholangiopancreatography are recent notable advances in this field. This review explores the aforementioned state-of-the-art techniques by focusing on their clinical applications and potential benefits, as well as their likely future direction.

Two-shot compressed sensing techniques accelerate cardiac cine sequence acquisition and quantitative evaluation of the diagnostic efficacy / 第二军医大学学报

Objective To perform cardiac magnetic resonance (CMR) examination with 2-shot compressed sensing (CS) cardiac cine imaging (cine) technique, so as to obtain high-quality images that can quickly and accurately assess cardiac function and are closer to the standard cine sequence. Methods The patients, who underwent CMR examination in Department of Radiology of Peking Union Medical College Hospital of Chinese Academy of Medical Sciences & Peking Union Medical College from Jul. to Sep. 2018, were continuously enrolled. All enrolled patients received the standard cine sequence, single-shot (ss) CS cine sequence and 2-shot CS cine sequence image acquisition. Quantitative analyses of image quality and cardiac function were performed on each cine image acquired from different sequences. Results Twenty-two patients completed the three types of cine sequences. The average acquisition time of standard cine sequence, ss CS cine sequence and 2-shot CS cine sequence was (102.50±18.55), (20.50±3.71) and (30.75±5.57) s, respectively. The median total image quality scores of the standard, ss CS and 2-shot CS cine sequences were 4, 3 and 4, respectively. There was significant difference in the total quality scores between the standard cine sequence and the ss CS cine sequence (Z=-2.828, P=0.005), while there was no significant difference between the standard cine sequence and the 2-shot CS cine sequence (Z=-1.000, P=0.317). In the quantitative study of cardiac function parameters, left ventricular myocardial mass was significantly different between the standard cine sequence and the ss CS cine sequence (100.25 [47.30-136.02] g vs 101.25 [48.30-135.30] g, Z=-2.484, P=0.013), but there were no significant differences in the other parameters. There were no significant differences in the cardiac function parameters between the standard cine sequence and the 2-shot cine sequence. Spearman correlation analysis showed that there were good correlations in the cardiac function parameters between the standard cine and the ss CS cine, and the standard cine and the 2-shot CS cine (all P<0.01). Conclusion The acquisition time of 2-shot CS cine and ss CS cine sequences is significantly shorter than that of standard cine sequence. However, 2-shot CS cine sequence can obtain images closer to the images obatined by standard cine sequence, which can be use d to accurately evaluate the cardiac function.

Comparison of compressed sensing and parallel imaging applied to contrastGenhanced MRI of liver / 实用放射学杂志

Objective To compare the compressed sensing (CS)and parallel imaging (PI)techniques applied to contrast-enhanced MRI (CE-MRI)scanning of liver and to determine their clinical applicability.Methods Thirty patients with liver mass who underwent the CE-MRI scanning with both CS and PI techniques were recruited in the current study.The SNR of the liver,acquisition time and subjective image quality scores were compared between CS (CE-MRI with CS)and PI (CE-MRI with PI)groups respectively.Results The SNR values of pre-enhancement T1 WI in CS group were lower than those in PI group (1 97.82±32.5 3 vs 204.94±35.28,P＜0.05).However,there was no significant difference in the SNR values of images in equilibrium phase between the two groups (CS vs PI:392.38±72.93 vs 405.03±82.09,P＞0.05).The acquisition time in CS group was significantly shorter than that in PI group [(11.71±0.23)s vs (17.85±0.42)s, P＜0.01].Significantly higher subjective image quality scores were found in CS group than those in PI group (3.54±0.57 vs 2.91±0.80,P＜0.01). Conclusion CS technique may benefit the patients who cannot hold breath well and improve the CE-MRI image quality.

Compressed sensing magnetic resonance image reconstruction based on double sparse model / 生物医学工程学杂志

The medical magnetic resonance (MR) image reconstruction is one of the key technologies in the field of magnetic resonance imaging (MRI). The compressed sensing (CS) theory indicates that the image can be reconstructed accurately from highly undersampled measurements by using the sparsity of the MR image. However, how to improve the image reconstruction quality by employing more sparse priors of the image becomes a crucial issue for MRI. In this paper, an adaptive image reconstruction model fusing the double dictionary learning is proposed by exploiting sparse priors of the MR image in the image domain and transform domain. The double sparse model which combines synthesis sparse model with sparse transform model is applied to the CS MR image reconstruction according to the complementarity of synthesis sparse and sparse transform model. Making full use of the two sparse priors of the image under the synthesis dictionary and transform dictionary learning, the proposed model is tackled in stages by the iterative alternating minimization algorithm. The solution procedure needs to utilize the synthesis and transform K-singular value decomposition (K-SVD) algorithms. Compared with the existing MRI models, the experimental results show that the proposed model can more efficiently improve the quality of the image reconstruction, and has faster convergence speed and better robustness to noise.

Increasing the quality of reconstructed signal in compressive sensing utilizing Kronecker technique

Quality of reconstruction of signals sampled using compressive sensing (CS) algorithm depends on the compression factor and the length of the measurement. A simple method to pre-process data before reconstruction of compressively sampled signals using Kronecker technique that improves the quality of recovery is proposed. This technique reduces the mutual coherence between the projection matrix and the sparsifying basis, leading to improved reconstruction of the compressed signal. This pre-processing method changes the dimension of the sensing matrix via the Kronecker product and sparsity basis accordingly. A theoretical proof for decrease in mutual coherence using the proposed technique is also presented. The decrease of mutual coherence has been tested with different projection matrices and the proposed recovery technique has been tested on an ECG signal from MIT Arrhythmia database. Traditional CS recovery algorithms has been applied with and without the proposed technique on the ECG signal to demonstrate increase in quality of reconstruction technique using the new recovery technique. In order to reduce the computational burden for devices with limited capabilities, sensing is carried out with limited samples to obtain a measurement vector. As recovery is generally outsourced, limitations due to computations do not exist and recovery can be done using multiple measurement vectors, thereby increasing the dimension of the projection matrix via the Kronecker product. The proposed technique can be used with any CS recovery algorithm and be regarded as simple pre-processing technique during reconstruction process.

Two-dimensional Reconstruction and Three-dimensional Visualization of MRI Images Based on Compressed Sensing / 中国医学影像学杂志

Compressed sensing (CS) is a novel theoretical framework for information acquisition and processing. Taking advantages of the sparsity or compressibility of the signals inherent in the real world, compressed sensing can collect compressed data at the sampling rate much lower than that needed in Shannon's theorem based on random measurement matrix. This technique is used in medical imaging to accelerate MRI's scanning speed, reduce radiation dosage and alleviate patients' suffering. The whole process of the proposed algorithm was as follows: firstly, the wavelet transform was applied to achieve sparse representation of medical images and reserve certain parts with maximal coefficients; secondly, the reconstruction based on CS theory were achieved according to the improved optimized orthogonal matching pursuit (OOMP) algorithm;finally, maximum intensity projection algorithm was used to achieve three-dimensional volume reconstruction. The experimental results demonstrated that our proposed two-dimensional reconstruction method was accurate and effective, which was verified qualitatively by the local detail magnification of images and quantitatively by peak signal-to-noise ratio and sectional comparison. Therefore, the three-dimensional reconstruction can be rather helpful in clinic diagnosis and treatment.

Fast Cardiac CINE MRI by Iterative Truncation of Small Transformed Coefficients

PURPOSE: A new compressed sensing technique by iterative truncation of small transformed coefficients (ITSC) is proposed for fast cardiac CINE MRI. MATERIALS AND METHODS: The proposed reconstruction is composed of two processes: truncation of the small transformed coefficients in the r-f domain, and restoration of the measured data in the k-t domain. The two processes are sequentially applied iteratively until the reconstructed images converge, with the assumption that the cardiac CINE images are inherently sparse in the r-f domain. A novel sampling strategy to reduce the normalized mean square error of the reconstructed images is proposed. RESULTS: The technique shows the least normalized mean square error among the four methods under comparison (zero filling, view sharing, k-t FOCUSS, and ITSC). Application of ITSC for multi-slice cardiac CINE imaging was tested with the number of slices of 2 to 8 in a single breath-hold, to demonstrate the clinical usefulness of the technique. CONCLUSIONS: Reconstructed images with the compression factors of 3-4 appear very close to the images without compression. Furthermore the proposed algorithm is computationally efficient and is stable without using matrix inversion during the reconstruction.

High Resolution Time Resolved Contrast Enhanced MR Angiography Using k-t FOCUSS

PURPOSE: Recently, the Recon Challenge at the 2009 ISMRM workshop on Data Sampling and Image Reconstruction at Sedona, Arizona was held to evaluate feasibility of highly accelerated acquisition of time resolved contrast enhanced MR angiography. This paper provides the step-by-step description of the winning results of k-t FOCUSS in this competition. MATERIALS AND METHODS: In previous works, we proved that k-t FOCUSS algorithm successfully solves the compressed sensing problem even for less sparse cardiac cine applications. Therefore, using k-t FOCUSS, very accurate time resolved contrast enhanced MR angiography can be reconstructed. Accelerated radial trajectory data were synthetized from X-ray cerebral angiography images and provided by the organizing committee, and radiologists double blindly evaluated each reconstruction result with respect to the ground-truth data. RESULTS: The reconstructed results at various acceleration factors demonstrate that each components of compressed sensing, such as sparsifying transform and incoherent sampling patterns, etc can have profound effects on the final reconstruction results. CONCLUSION: From reconstructed results, we see that the compressed sensing dynamic MR imaging algorithm, k-t FOCUSS enables high resolution time resolved contrast enhanced MR angiography.

High Resolution Time Resolved Contrast Enhanced MR Angiography Using k-t FOCUSS

PURPOSE: Recently, the Recon Challenge at the 2009 ISMRM workshop on Data Sampling and Image Reconstruction at Sedona, Arizona was held to evaluate feasibility of highly accelerated acquisition of time resolved contrast enhanced MR angiography. This paper provides the step-by-step description of the winning results of k-t FOCUSS in this competition. MATERIALS AND METHODS: In previous works, we proved that k-t FOCUSS algorithm successfully solves the compressed sensing problem even for less sparse cardiac cine applications. Therefore, using k-t FOCUSS, very accurate time resolved contrast enhanced MR angiography can be reconstructed. Accelerated radial trajectory data were synthetized from X-ray cerebral angiography images and provided by the organizing committee, and radiologists double blindly evaluated each reconstruction result with respect to the ground-truth data. RESULTS: The reconstructed results at various acceleration factors demonstrate that each components of compressed sensing, such as sparsifying transform and incoherent sampling patterns, etc can have profound effects on the final reconstruction results. CONCLUSION: From reconstructed results, we see that the compressed sensing dynamic MR imaging algorithm, k-t FOCUSS enables high resolution time resolved contrast enhanced MR angiography.

Reducción de los tiempos de adquisición de imágenes por resonancia magnética utilizando técnicas de compressed sensing / Reduction of the acquisition time in magnetic resonance imaging using compressed sensing

Introduction: The acquisition process in magnetic resonance images (MRI) is slow. One approach to reduce the acquisition times is the reconstruction of undersampled data. i.e. to acquire less samples that those needed for standard application, and to reconstruct the unknown samples using mathematical algorithms. We propose to used reconstruction techniques for undersampled data based on Compressed Sensing (CS) to decrease the acquisition times, obtaining identical MRI as those obtained with all samples. Methods: We performed reconstructions of undersampled data obtained from phantoms and MRI with 60 percent, 55 percent and 50 percent of the samples. Results: When the number of samples was more that the double of pixels with non cero intensity, the reconstructions where identical to the original ones. For the MRI experiment, this was achieved with 60 percent of the samples, therefore obtaining a 40 percent of reduction in the acquisition time. Discussion: Our reconstruction technique based on CS is an effective way for reducing the acquisition times in MRI.

Introducción: El proceso de adquisición de imágenes por resonancia magnética (IRM) es lento. Una forma para disminuir los tiempos de adquisición es a través de reconstrucciones de datos submuestreados, es decir tomar menos muestras que las necesarias en aplicaciones estándares, y reconstruir las muestras faltantes a través de algoritmos matemáticos. Proponemos utilizar técnicas de reconstrucción de datos submuestreados basadas en técnicas de Compressed Sensing (CS) para disminuir los tiempos de adquisición, obteniendo imágenes idénticas a las obtenidas con todas las muestras. Métodos: Realizamos reconstrucciones de datos submuestreados de fantomas y IRM con 60 por ciento, 55 por ciento y 50 por ciento de las muestras. Resultados: Cuando el número de muestras fue mayor al doble del número de pixeles con intensidad cero, las reconstrucciones obtenidas fueron idénticas a las originales. Para las IRM esto se logró con 60 por ciento de las muestras, logrando reducciones del 40 por ciento en los tiempos de adquisición. Discusión: Nuestra técnica de reconstrucción basada en CS es una forma efectiva para reducir los tiempos de adquisición de IRM.