Parallel Acquisition Technique Research Articles

Single-shot frequency offset measurement with HASTE using the selective parity approach.

Measurements of frequency offset are commonly required in MRI. The standard method measures the signal phase as a function of evolution time. Here we use a single shot turbo-spin-echo acquisition method to measure frequency offset at a single evolution time. After excitation the transverse magnetisation evolves during the evolution time, and is then repeatedly refocused. The phase is conjugated between alternate echoes. Using partial parallel acquisition techniques we obtain separate odd- and even- echo images. An iterative procedure ensures self-consistency between them. The difference in phase between the two images yields frequency offset maps. The technique was implemented at 3 Tesla and tested on a healthy human volunteer for a range of evolution times between 6 and 42ms. A standard method using a similar readout train and multiple evolution times was used as a gold-standard measure. In a statistical comparison with the gold standard no evidence for bias or offset was found. There was no systematic variation in precision or accuracy as a function of evolution time. We conclude that the presented approach represents a viable method for the rapid generation of frequency offset maps with a high image quality and minimal distortion.

Deep Learning-reconstructed Parallel Accelerated Imaging for Knee MRI

Deep learning (DL) can improve image quality by removing noise from accelerated MRI. To compare the quality of various accelerated imaging applications in knee MRI with and without DL. We analyzed 44 knee MRI scans from 38 adult patients using the DL-reconstructed parallel acquisition technique (PAT) between May 2021 and April 2022. The participants underwent sagittal fat-saturated T2-weighted turbo-spin-echo accelerated imaging without DL (PAT-2 [2-fold parallel accelerated imaging], PAT-3, and PAT-4) and with DL (DL with PAT-3 [PAT-3DL] and PAT-4 [PAT-4DL]). Two readers independently evaluated subjective image quality (diagnostic confidence of knee joint abnormalities, subjective noise and sharpness, and overall image quality) using a 4-point grading system (1-4, 4=best). Objective image quality was assessed based on noise (noise power) and sharpness (edge rise distance). The mean acquisition times for PAT-2, PAT-3, PAT-4, PAT-3DL, and PAT-4DL sequences were 2:55, 2:04, 1:33, 2:04, and 1:33 min, respectively. Regarding subjective image quality, PAT-3DL and PAT-4DL scored higher than PAT-2. Objectively, DL-reconstructed imaging had significantly lower noise than PAT-3 and PAT-4 (P <0.001), but the results were not significantly different from those for PAT-2 (P >0.988). Objective image sharpness did not differ significantly among the imaging combinations (P =0.470). The inter-reader reliability ranged from good to excellent (κ = 0.761–0.832). PAT-4DL imaging in knee MRI exhibits similar subjective image quality, objective noise, and sharpness levels compared with conventional PAT-2 imaging, with an acquisition time reduction of 47%.

Multi-mode metasurface as a receive coil for magnetic resonance imaging

Sensitivity and diagnostic capabilities of magnetic resonance imaging (MRI) are dictated by the design of radio frequency (RF) receive coils. They must possess several key characteristics, such as a high signal-to-noise ratio (SNR), for image quality enhancement and multiple channels for scan time reduction. Artificial materials with tailored properties, such as metasurfaces, when used as RF coils, have been shown to deliver increased image quality or scan safety. Here, we suggest and describe a multi-mode metasurface-based coil with two independent receive channels. We experimentally show that such a coil provided a higher SNR than a state-of-the-art dedicated coil. We also demonstrate the feasibility of two intrinsic independent receive channels coexisting on the same frequency, enabling parallel signal acquisition techniques.

Simultaneous Multislice Accelerated TSE for Improved Spatiotemporal Resolution and Diagnostic Accuracy in Magnetic Resonance Neurography: A Feasibility Study.

This study aims to evaluate the utility of simultaneous multislice (SMS) acceleration for routine magnetic resonance neurography (MRN) at 3 T. Patients with multiple sclerosis underwent MRN of the sciatic nerve consisting of a standard fat-saturated T2-weighted turbo spin echo (TSE) sequence using integrated parallel acquisition technique (PAT2) acceleration and 2 T2 TSE sequences using a combination of PAT-SMS acceleration (1) to reduce scan time (PAT2-SMS2; SMS-TSE FAST ) and (2) for time neutral increase of in-plane resolution (PAT1-SMS2; SMS-TSE HR ). Acquisition times were 5:29 minutes for the standard T2 TSE, 3:12 minutes for the SMS-TSE FAST , and 5:24 minutes for the SMS-TSE HR . Six qualitative imaging parameters were analyzed by 2 blinded readers using a 5-point Likert scale and T2 nerve lesions were quantified, respectively. Qualitative and quantitative image parameters were compared, and both interrater and intrarater reproducibility were statistically assessed. In addition, signal-to-noise ratio/contrast-to-noise ratio (CNR) was obtained in healthy controls using the exact same imaging protocol. A total of 15 patients with MS (mean age ± standard deviation, 38.1 ± 11 years) and 10 healthy controls (mean age, 29.1 ± 7 years) were enrolled in this study. CNR analysis was highly reliable (intraclass correlation coefficient, 0.755-0.948) and revealed a significant CNR decrease for the sciatic nerve for both SMS protocols compared with standard T2 TSE (SMS-TSE FAST /SMS-TSE HR , -39%/-55%; P ≤ 0.01). Intrarater and interrater reliability of qualitative image review was good to excellent (κ: 0.672-0.971/0.617-0.883). Compared with the standard T2 TSE sequence, both SMS methods were shown to be superior in reducing pulsatile flow artifacts ( P < 0.01). Ratings for muscle border sharpness, detailed muscle structures, nerve border sharpness, and nerve fascicular structure did not differ significantly between the standard T2 TSE and the SMS-TSE FAST ( P > 0.05) and were significantly better for the SMS-TSE HR than for standard T2 TSE ( P < 0.001). Muscle signal homogeneity was mildly inferior for both SMS-TSE FAST ( P > 0.05) and SMS-TSE HR ( P < 0.001). A significantly higher number of T2 nerve lesions were detected by SMS-TSE HR ( P ≤ 0.01) compared with the standard T2 TSE and SMS-TSE FAST , whereas no significant difference was observed between the standard T2 TSE and SMS-TSE FAST . Implementation of SMS offers either to substantially reduce acquisition time by over 40% without significantly impeding image quality compared with the standard T2 TSE or to increase in-plane resolution for a high-resolution approach and improved depiction of T2 nerve lesions while keeping acquisition times constant. This addresses the specific needs of MRN by providing different imaging approaches for 2D clinical MRN.

Study on Memory Function of Stroke Patients under Exercise Relearning Based on DWI Image Analysis Based on Optimized Registration Algorithm

Objective. This paper uses an optimized registration algorithm to analyze the diffusion-weighted imaging (DWI) scan parameters of acute ischemic stroke (AIS) in the memory function of stroke patients under exercise relearning (MRP). Methods. This study used a random case-control study. 65 patients with stroke and hemiplegia were randomly divided into a control group: conventional rehabilitation intervention (32 cases), and a treatment group: MRP (33 cases). Each patient uses 4 parameters for DWI examination and obtains 4 sets of images, group 1 is the control sequence, group 2 uses parallel acquisition technology, group 3 uses parallel acquisition technology and reduces the number of excitations, group 4 uses parallel acquisition technology to reduce repetition time (TR) and echo time (TE) and enlarge the field of view, and the scan time of each group is 177, 81, 23, and 18 s in sequence. At the time of enrollment and after 12 weeks of treatment, patients in each group were evaluated with Fugl-Meyer motor function score (FMA) and modified Pap index (MBI) for hand and wrist motor function and ADL. Results. After treatment, the FMA and MBI values of the treatment group were significantly higher than those of the control group ( P &lt; 0.05 ). Conclusion. By adopting a parallel acquisition technique and reducing the number of excitations (group 3) scanning scheme, not only the scanning time is significantly shortened, but also the image quality can meet the diagnostic requirements, which has great application value for AIS patients who need emergency treatment. MRP can obviously promote the hand and wrist motor function and daily living ability of stroke hemiplegic patients.

Clinical feasibility of simultaneous multislice acceleration in knee MRI

PurposeTo find the best simultaneous multislice (SMS) accelerated setting for clinical application in knee MRI. Material and methodsThirty-three patients (mean age, 54 years; 21 women) who underwent knee MRI (conventional/SMS sequences) between June and October 2020 were enrolled. Two radiologists retrospectively evaluated sagittal T1- and T2-weighted conventional (2-fold parallel acquisition technique [PAT-2]) and SMS (SMS-2 [PAT-2 with 2-fold SMS], SMS-3, and SMS-4) images. For qualitative analysis, artifacts (zebra/residual aliasing) and diagnostic confidence for internal derangement of knee (bone marrow, cartilage, meniscus, anterior cruciate ligament, and synovium abnormalities) were evaluated. For quantitative analysis, contrast-to-noise ratios of bone marrow, meniscus, joint effusion, and ligament were evaluated. ResultsCompared to PAT-2 (2 min 32 s), mean acquisition time was reduced by 47% in SMS-2; 64%, SMS-3; and 70%, SMS-4. In qualitative analysis, zebra artifacts were only seen on T2-weighted SMS images. The more SMS was applied, the more zebra and residual aliasing artifacts were seen and the lower diagnostic confidence was for internal derangement. However, qualitative analysis showed acceptable image quality in SMS-2 and SMS-3 images, but not in SMS-4 images. In quantitative analysis, SMS-4 images showed the lowest contrast-to-noise ratios and there were no significant differences among PAT-2, SMS-2, and SMS-3 images. ConclusionApplying SMS-3 to knee MRI reduced scan time and showed acceptable image quality compared to conventional (PAT-2). However, when evaluating SMS images, radiologists should know that when more SMS is applied, more zebra and residual aliasing artifacts appear.

Compressed sensing regularized calibrationless parallel magnetic resonance imaging via deep learning

The longer scanning time requirement in Magnetic Resonance Imaging (MRI) can one way be overcome through parallel data acquisition technique. The scanning time in pMRI systems can further be reduced through calibrationless data acquisition process that eliminates the need of extra k-space data. Compressed Sensing (CS) or Compressive Sampling in data acquisition again reduces this scanning time as image reconstruction is done from the undersampled k-space measurements. To this aim, the present work proposes a calibrationless CS regularized pMRI approach. A Stacked Convolutional Denoising Autoencoder (SCDAE) is used for accurate estimation of the coil-wise sensitivity maps. The present work also uses an interferometry modulated Radio Frequency (RF) coil that not only enhances the resolution in the Field of View (FoV), but also reduces the interference on the adjacent FoVs. Extensive simulation results show that the proposed method enables reconstruction of an MR image with size 256 × 256 from 25% measurements in approximately 0.57 s and offers a performance improvement in Peak-Signal-to-Noise Ratio (PSNR) by 2 ± 0.18 dB and Structural SIMilarity (SSIM) by 0.2 ± 0.06 over the state-of-the-art methods.

Estimation error bound for GRAPPA diffusion-weighted MRI

In recent years, diffusion weight magnetic resonance imaging (DW-MRI) has become one of the most important MRI imaging modalities. The importance of the DW-MRI grew thanks to the combination of parallel magnetic resonance imaging (pMRI) techniques with the echo-planar imaging (EPI), which minimize scan time and lead to reduced distortion, allowing the DW-MRI to become a routine clinical exam. Additionally, this has brought various new parameters that influence image quality and biomarkers used in DW-MRI. This work aims to investigate the effects of these parameters on the estimation quality, by using the Cramér-Rao bound tool, which gives analytical expressions of the lower limit on the estimation error variance of different DW-MRI variables when using the pMRI technique. In particular, these bounds will be used to study and optimize the impact of different factors of generalized autocalibrating partially parallel acquisition (GRAPPA) technique and system parameters on the estimation quality of the desired clinical metrics. Moreover, the obtained results of this study can be exploited and adapted in all human body DW-MRI clinical routines, further improving disease diagnosis, and tractography studies.

Evaluation of left ventricular strain in patients with arrhythmia based on the 3T MR temporal parallel acquisition technique

Most of the current studies on myocardial strain are mainly applied in patients with sinus rhythm because the image quality of arrhythmias obtained with conventional scanning sequences does not meet diagnostic needs. Here, we intend to assess left ventricular (LV) global myocardial strain in patients with arrhythmias with 3 Tesla magnetic resonance (MR) and a new cine sequence. Thirty-three patients with arrhythmia and forty-eight subjects with sinus rhythm were enrolled in the study. LV myocardial thickness, cardiac function, myocardial strain and the apparent contrast-to-noise ratio (CNR) were all measured and compared using images generated by the real-time temporal parallel acquisition technique (TPAT) and the conventional cine sequence. In the arrhythmia group, the image quality of real-time TPAT was significantly better than that of the conventional cine sequence. In the arrhythmia group, the LV global peak radial strain and global peak circumferential strain values of real-time TPAT were significantly different from those of the conventional technique (radial strain, conventional: 20.27 ± 15.39 vs. TPAT: 24.14 ± 15.85, p = 0.007; circumferential strain, conventional:−12.06 ± 6.60 vs. TPAT: −13.71 ± 6.31, p = 0.015). There was no significant difference in global peak longitudinal strain between real-time TPAT and the conventional technique (−10.94 ± 4.66 vs. −10.70 ± 5.96, p = 0.771). There was no significant difference in the cardiac function parameters between the two techniques (p > 0.05), but there was a significant difference in 12 segments of the LV wall thickness between the two sequences (p < 0.05). In the sinus rhythm group, image quality using real-time TPAT was comparable to that using the conventional technique, and there was no significant difference in any of the indices (p > 0.05). Real-time TPAT is an effective method for detection of left ventricular myocardial deformation in patients with arrhythmia.

Image quality of the CAIPIRINHA-Dixon-TWIST-VIBE technique for ultra-fast breast DCE-MRI: Comparison with the conventional GRE technique

PurposeThe aim of this study was to evaluate image quality of the CAIPIRINHA-Dixon-TWIST-Volume-Interpolated Breath-hold Examination (CDT-VIBE) technique for ultra-fast breast dynamic contrast enhanced (DCE) MRI with respect to conventional Gradient-Recalled Echo (GRE) technique. MethodsA total of 58 patients underwent a DCE-MRI based on CDT-VIBE sequence (temporal resolution: 11.9 s), immediately followed by 1 phase of a conventional T1 weighted GRE sequence (acquisition time: 68 s). The Signal-to-Noise Ratio (SNR) on phantom images, lesion/parenchyma signal ratio (LPSR), image quality, and morphological characterization were compared between the last phase of CDT-VIBE and conventional GRE images. The image quality was assessed by visual grading analysis (VGA). Reader agreement was assessed using Kappa analysis. ResultsThere was no significant difference in SNR (phantom) or LPSR (patient) between CDT-VIBE and conventional GRE images (P > 0.05). Significant parallel acquisition technique (PAT) noise and mild blurriness was observed on CDT-VIBE images. Visual grading analysis (VGA) confirmed significantly worse ratings for CDT-VIBE compared to the conventional GRE sequence in terms of PAT noise, lesion’s internal feature clarity, and therefore overall image quality (area under contrast curve [AUC] values: 0.578 ‒ 0.764, P < 0.05), but edge sharpness and lesion conspicuity were equivalent (P > 0.05). Kappa analysis revealed good agreement on image quality scores (к = 0.725 ‒ 0.908) and on morphologic terms (к = 0.745–1.000). ConclusionThe CDT-VIBE sequence provides excellent spatial resolution and adequate image quality in ultra-fast breast DCE-MRI. Further improvement in PAT noise and internal structure blurriness may be necessary.

High-resolution MRI using compressed sensing-sensitivity encoding (CS-SENSE) for patients with suspected neurovascular compression syndrome: comparison with the conventional SENSE parallel acquisition technique

To retrospectively compare sensitivity encoding (SENSE) and compressed sensing-sensitivity encoding (CS-SENSE) for high resolution (HR) cranial nerve magnetic resonance imaging (MRI) in a clinical population. Twenty consecutive patients who were clinically suspected of neurovascular compression syndrome (NVCS) were enrolled in this study. HR three-dimensional isotropic T2-weighted fast spin-echo (T2 VISTA) sequences with SENSE or CS-SENSE, and contrast-enhanced three-dimensional T1-turbo field-echo (CE 3D T1 TFE) with SENSE or CS-SENSE, were compared using quantitative and qualitative methods by two board-certified neuroradiologists. For the T2 VISTA, CS-SENSE was significantly superior to SENSE in terms of cerebrospinal fluid homogeneity. For CE 3D T1 TFE, CS-SENSE was significantly superior to SENSE in terms of the existence of ghost artefact and the signal-to-noise ratio (SNR) of the pontine parenchyma. There was no significant difference in overall image quality between the two techniques. Compared with SENSE, CS-SENSE reduced the scan time to 44.2% of that with SENSE on T2 VISTA, and to 66.1% of that with SENSE of the CE 3D T1 TFE, with the differences being statistically significant (p<0.01, both). For T2 VISTA and CE 3D T1 TFE imaging of patients with suspected NVCS, CS-SENSE appears to offer superior reductions in motion artefact and scan time relative to SENSE, without a loss of overall image quality.

Energy saving and emission reduction of fossil energy based on low carbon economy and its consumption structure optimization

Abstract Energy saving and emission reduction have been not only a slogan but also a policy in this modern society where the phenomenon of greenhouse is exacerbated. In this study, calculation method of carbon emission and integrated parallel acquisition technique (IPAT) scenario prediction model were combined to predict the changes of total carbon emissions, energy structure distribution, and carbon emission intensity under three measures of energy saving and emission reduction in the next ten years in Shandong, China. The results showed that the total carbon emission increased year by year, and the coal ratio and carbon emission intensity decreased under the natural scenario; the total carbon emission in the weakly constrained scenario would increase annually until 2029, the amplitude was smaller than that of the natural scenario, while the coal ratio and carbon emission intensity would decrease, and the amplitude was larger than that of the natural scenario. Under the strongly constrained scenario, the total carbon emission would increase annually before 2025, and the amplitude was smaller than the weakly constrained scenario, while the coal ratio and carbon emission intensity would decrease, and the amplitude was larger than the weakly constrained scenario.

Compressed Sensing Radial Sampling MRI of Prostate Perfusion: Utility for Detection of Prostate Cancer.

Purpose To investigate the diagnostic performance of a dual-parameter approach by combining either volumetric interpolated breath-hold examination (VIBE)- or golden-angle radial sparse parallel (GRASP)-derived dynamic contrast agent-enhanced (DCE) MRI with established diffusion-weighted imaging (DWI) compared with traditional single-parameter evaluations on the basis of DWI alone. Materials and Methods Ninety-four male participants (66 years ± 7 [standard deviation]) were prospectively evaluated at 3.0-T MRI for clinical suspicion of prostate cancer. Included were 101 peripheral zone prostate cancer lesions. Histopathologic confirmation at MRI transrectal US fusion biopsy was matched with normal contralateral prostate parenchyma. MRI was performed with diffusion weighting and DCE by using GRASP (temporal resolution, 2.5 seconds) or VIBE (temporal resolution, 10 seconds). Perfusion (influx forward volume transfer constant [Ktrans] and rate constant [Kep]) and apparent diffusion coefficient (ADC) parameters were determined by tumor volume analysis. Areas under the receiver operating characteristic curve were compared for both sequences. Results Evaluated were 101 prostate cancer lesions (GRASP, 61 lesions; VIBE, 40 lesions). In a combined analysis, diffusion and perfusion parameters ADC with Ktrans or Kep acquired with GRASP had higher diagnostic performance compared with diffusion characteristics alone (area under the curve, 0.97 ± 0.02 [standard error] vs 0.93 ± 0.03; P < .006 and .021, respectively), whereas ADC with perfusion parameters acquired with VIBE had no additional benefit (area under the curve, 0.94 ± 0.03 vs 0.93 ± 0.04; P = .18and .50, respectively, for combination of ADC with Ktrans and Kep). Conclusion If used in a dual-parameter model, incorporating diffusion and perfusion characteristics, the golden-angle radial sparse parallel acquisition technique improves the diagnostic performance of multiparametric MRI examinations of the prostate. This effect could not be observed combining diffusing with perfusion parameters acquired with volumetric interpolated breath-hold examination. © RSNA, 2018.

Simultaneous multi-slice accelerated turbo spin echo of the knee in pediatric patients.

To compare knee MRI performed with the integrated parallel acquisition technique (PAT) and simultaneous multislice (SMS) turbo spin echo (TSE) T2-weighted (T2w) sequences with conventional TSE sequences in pediatric patients. This was a retrospective IRB-approved study. Seventy-four subjects (26 male, 48 female, mean age 15.3years, range 8-20) underwent 3-T MRI of the knee with a T2w TSE pulse sequence prototype with four-fold PAT and SMS acceleration as well as the standard PAT-only accelerated sequences. Images were anonymized and two study folders were created: one examination with only T2w PAT2 images (conventional examination) and one examination with only T2w SMS2/PAT2 sequences (SMS examination). Two readers rated examinations for 15 specific imaging findings and 5 quality metrics. Interreader agreement was measured. Signal to noise (SNR) and contrast to noise (CNR) were measured for SMS and conventional T2w sequences. Consensus review demonstrated diagnostic quality performance of SMS examinations with respect to all 15 structures. Average area under the curve (AROC) was 0.95 and 0.97 for readers 1 and 2, respectively. The conventional sequence was favored over SMS for four out of five quality metrics (p < 0.001). SNR and CNR were higher for the conventional sequences compared to SMS. SMS accelerated T2w TSE sequences offer a faster alternative for knee imaging in pediatric patients without compromise in diagnostic performance despite diminished SNR. The four-fold acceleration of SMS is beneficial to pediatric patients who often have difficulty staying still for long MRI examinations.

Afterglow Solid-State NMR Spectroscopy.

Biomolecular solid-state NMR experiments have traditionally been collected through detection of 13C or 15N nuclei. Since these nuclei have relatively low sensitivity stemming from their smaller gyromagnetic ratios relative to 1H, the time required to collect multi-dimensional datasets serves as a limitation to resonance assignment and structure determination. One improvement in the field has been to employ simultaneous or parallel acquisition techniques with the goal of acquiring more than one dataset at a time and therefore speeding up the overall data collection process. Central to these experiments is the cross-polarization (CP) element, which serves as a way to transfer magnetization between nuclei via magnetic dipolar couplings. In this chapter, we show how residual signal remaining after CP is a polarization source that can be used to acquire additional datasets. The setup of this class of experiments, referred to as Afterglow spectroscopy, is described and demonstrated using a membrane protein transporter involved in multidrug resistance.

Further considerations on hepatic lesion discrimination using diffusion MR imaging.

With great interest, we read the article "Differential diagnosis between hepatic metastases and benign focal lesions using DWI with parallel acquisition technique: a meta-analysis" (by Wei CG et al.). This article suggests that diffusion-weighted imaging was useful for differentiation between hepatic metastases and benign focal lesions. The result is encouraging. We would like to contribute regarding the value of DWI with parallel acquisition technique in the differentiation of metastases and benign hepatic lesions.

Analisis Informasi Anatomi Dengan dan Tanpa Parallel Acquisition Technique Menggunakan Sekuen 2D Thick Slab Single Shot Fast Spin Echo pada Pemeriksaan Magnetic Resonance Cholangiopancreatography (MRCP)

Backgroud: 2D thick slab single shot fast spin echo (SSFSE) sequence in MRCP examination is a sequence of fast spin echo (FSE) which has a long turbo factor so that the time of acquisition in this sequence is longer than usual that will potentially cause image blurring. Parallel acquisition or SENSE technique is a technique used to reduce acquisition time and improve spatial resolution. The purpose of this study was to determine differences in anatomical information with and without parallel acquisition technique in 2D thick slab SSFSE sequences on MRCP examination.Methods: This research was an experimental study. This research was conducted by Philips 1.5 T MRI unit in dr. S Hardjolukito Yogyakarta Hospital. Data were 20 MRCP images from 10 normal volunteers with and without parallel acquisition technique on sequences of 2D thick slab SSFSE. Assessment of the images was conducted qualitatively in the form of respondents's assessment of the clearance of anatomical information includes the gallbladder, right hepatic duct, left hepatic duct, common bile duct, common hepatic duct, cystic duct, and the main pancreatic duct. Quantitative data analyzed by Cohen's Kappa test, cross tabulation, and Wilcoxon tests.Results: The result showed that there was a difference between the clearance of the overall anatomical information between 2D thick slab SSFSE sequences with and without parallel acquisition technique in MRCP with p = 0.000 (p-value 0.05), based on the mean rank obtained sequences of 2D thick slab SSFSE SENSE (14.50) better than the 2D thick slab SSFSE (0.00). Analysis of each anatomy showed significant differences in all organs except the gallbladder p = 0.059, p = left hepatic duct and the common bile duct 0.059 with p = 0.08.Conclusion: Parallel acquisition technique (SENSE) was well used because it has a faster acquisition time without decreasing image resolution.

Usefulness of metal artifact reduction with WARP technique at 1.5 and 3T MRI in imaging metal-on-metal hip resurfacings.

To evaluate the usefulness of the metal artifact reduction technique "WARP" in the assessment of metal-on-metal hip resurfacings at 1.5 and 3T in the context of image quality and imaging speed. Nineteen patients (25 hip resurfacings) were randomized for 1.5 and 3T MRI, both including T1 and T2 turbo spin-echo as well as turbo inversion recovery magnitude sequences with and without view angle tilting and high bandwidth. Additional 3T sequences were acquired with a reduced number of averages and using the parallel acquisition technique for accelerating imaging speed. Artifact size (diameter, area), image quality (5-point scale) and delineation of anatomical structures were compared among the techniques, sequences and field strengths using the Wilcoxon sign-rank and paired t-test with Bonferroni correction. At both field strengths, WARP showed significant superiority over standard sequences regarding image quality, artifact size and delineation of anatomical structures. At 3T, artifacts were larger compared to 1.5T without affecting diagnostic quality, and scanning time could be reduced by up to 64% without quality degradation. WARP proved useful in imaging metal-on-metal hip resurfacings at 1.5T as well as 3T with better image quality surrounding the implants. At 3T imaging could be considerably accelerated without losing diagnostic quality.

Fast Inner-Volume Imaging of the Lumbar Spine with a Spatially Focused Excitation Using a 3D-TSE Sequence

The purpose of this study was to evaluate the feasibility and technical quality of a zoomed three-dimensional (3D) turbo spin-echo (TSE) sampling perfection with application optimized contrasts using different flip-angle evolutions (SPACE) sequence of the lumbar spine. In this prospective feasibility study, nine volunteers underwent a 3-T magnetic resonance examination of the lumbar spine including 1) a conventional 3D T2-weighted (T2w) SPACE sequence with generalized autocalibrating partially parallel acquisition technique acceleration factor 2 and 2) a zoomed 3D T2w SPACE sequence with a reduced field of view (reduction factor 2). Images were evaluated with regard to image sharpness, signal homogeneity, and the presence of artifacts by two experienced radiologists. For quantitative analysis, signal-to-noise ratio (SNR) values were calculated. Image sharpness of anatomic structures was statistically significantly greater with zoomed SPACE (P < .0001), whereas the signal homogeneity was statistically significantly greater with conventional SPACE (cSPACE; P = .0003). There were no statistically significant differences in extent of artifacts. Acquisition times were 8:20 minutes for cSPACE and 6:30 minutes for zoomed SPACE. Readers 1 and 2 selected zSPACE as the preferred sequence in five of nine cases. In two of nine cases, both sequences were rated as equally preferred by both the readers. SNR values were statistically significantly greater with cSPACE. In comparison to a cSPACE sequences, zoomed SPACE imaging of the lumbar spine provides sharper images in conjunction with a 25% reduction in acquisition time.

Differential diagnosis between hepatic metastases and benign focal lesions using DWI with parallel acquisition technique: a meta-analysis.

We aim to investigate the diagnostic capability of diffusion-weighted imaging using parallel acquisition technique for the differentiation between hepatic metastases and benign focal lesions with a meta-analysis. The meta-analysis included a total of 858 hepatic metastases and 440 benign liver lesions from nine studies. The pooled sensitivity and specificity of diffusion-weighted imaging (DWI) were 0.87 (95% CI, 0.84-0.89) and 0.90 (95% CI, 0.87-0.93), respectively. The positive likelihood ratio (PLR) and negative likelihood ratio (NLR) were 8.50 (95% CI, 4.97-14.52) and 0.17 (95% CI, 0.11-0.26), respectively. The P value for χ (2) heterogeneity for all pooled estimates was <0.05. From the fitted summary receiver operating characteristics (SROC), the area under the curve (AUC) and Q* index were 0.95 and 0.88, respectively. Publication bias is not present (t = -0.76, P = 0.471). The meta-regression analysis indicated that evaluated covariates included patient number, patient population, mean age, maximum of b factor, number of cysts, number of hemangiomas, and field were not sources of heterogeneity (all P value >0.05). Diffusion-weighted imaging was useful for differentiation between hepatic metastases and benign focal lesions. The diffusion characteristics of the benign hepatocellular lesions, including cases of focal nodular hyperplasia (FNH) and adenoma, have rarely been reported and need further studies. The diagnostic capability of DWI with parallel acquisition technique for differentiation between metastases and benign hepatic focal lesions might be overestimated.