Ultrafast Intracranial Vessel Imaging With Non-Cartesian Spiral 3-Dimensional Time-of-Flight Magnetic Resonance Angiography at 1.5 T: An In Vitro and Clinical Study in Healthy Volunteers

Deep learning constrained compressed sensing reconstruction improves high-resolution three-dimensional (3D) T2-weighted turbo spin echo magnetic resonance imaging (MRI) of the lumbar spine

AIM

We sought to assess the image quality of three-dimensional (3D) T2-weighted (T2w) turbo spin echo (TSE) sequences with deep learning (DL)-constrained compressed sensing (CS) reconstruction relative to a reference two-dimensional (2D) T2w TSE sequence for routine clinical lumbar spine MRI.

MATERIALS AND METHODS

Fifty-three patients underwent imaging of the lumbar spine with a sagittal 2D T2w TSE sequence and with two CS-accelerated 3D T2w TSE sequences (voxel size of 0.4 × 0.4 × 0.5 mm) with CS factors of 7 and 11. The CS-accelerated sequences were reconstructed with iterative reconstruction with wavelet transformation (conventional CS) and secondly with a DL-constrained CS reconstruction (named CS-AI). Two readers graded image quality, based on 8 metrics (overall image quality, presence of image noise, presence of motion artifacts, delineation/conspicuity and clarity of anatomical structures such as the spinal cord, cauda equine nerve roots, cerebrospinal fluid (CSF), intervertebral disc, and bone marrow and intervertebral foramen) using Likert scales.

RESULTS

Overall inter-readout agreement was substantial (Krippendorff's α = 0.724, 95% confidence interval [CI]: 0.692-0.755). The CS7-AI and CS11-AI sequences were comparable or better than the 2D sequence in all 8 metrics (p < 0.001-p > 0.99). The CS7 and CS11 sequences were comparable or better than the 2D sequence in only 5 and 3 of the 8 metrics, respectively (p < 0.001-p > 0.99).

CONCLUSION

A DL-constrained CS reconstruction significantly improves the quality of accelerated high-resolution 3D T2w TSE imaging of the lumbar spine. Thus, high-quality imaging in a submillimeter resolution in all three imaging planes can be achieved without compromising the image quality as compared with standard 2D T2w TSE imaging.

Accelerating TOF-MRA: The impact of the combined use of compressed sensitivity encoding and spiral imaging

PURPOSE

To evaluate the image quality of the combined technique of compressed sensitivity encoding (CS) and spiral imaging in time-of-flight magnetic resonance angiography (TOF-MRA), which is approximately 2.5 times faster than conventional methods.

METHODS

Twenty volunteers underwent four TOF-MRA sequences: sensitivity encoding (SENSE) with acceleration factor of 4 (acquisition time: 4:55 min), CS with acceleration factor of 10.9, and spiral and CS-spiral (both 1:55 min). A quantitative image analysis (signal-to-noise ratio [SNR], contrast, and full width at half maximum [FWHM] edge criterion measurements) was performed on four TOF sequences. For qualitative image analysis, two board-certified radiologists evaluated the overall depiction of the proximal, intermediate, and distal branches in CS, spiral, and CS-spiral images using SENSE as a reference.

RESULTS

The SNR of BA in spiral and CS-spiral imaging was significantly lower than that in SENSE (p = 0.009). The contrasts of ACA and BA in CS-spiral were significantly higher and those in spiral were significantly lower than those in SENSE (p < 0.001). The FWHM in the CS image was significantly higher than that of SENSE; however, no significant differences were observed between the spiral or CS-spiral and SENSE. In qualitative analysis, the depiction of proximal vascular branches was significantly impaired in spiral than in others and that of distal vascular branches was significantly impaired in CS than in others (p < 0.001).

CONCLUSIONS

In TOF-MRA, which is approximately 2.5 times faster than conventional methods, the combined use of CS and spiral imaging demonstrated an improvement in image quality compared to either CS or spiral imaging alone.

SUMMARY STATEMENT

The image quality of Compressed SENSE and spiral imaging is particularly poor in the proximal and distal vascular branches, respectively at an extremely high acceleration factor; however, CS-spiral provided stable image quality in all regions as compared with the SENSE technique.

Clinical feasibility of CS-VIBE accelerates MRI techniques in diagnosing intracranial metastasis

Our objective was to evaluate and compare the diagnostic performance of post-contrast 3D compressed-sensing volume-interpolated breath-hold examination (CS-VIBE) and 3D T1 magnetization-prepared rapid-acquisition gradient-echo (MPRAGE) in detecting intracranial metastasis. Additionally, we analyzed and compared the image quality between the two. We enrolled 164 cancer patients who underwent contrast-enhanced brain MRI. Two neuroradiologists independently reviewed all the images. The signal-to-noise ratio (SNR), contrast-to noise ratio (CNR) were compared between two sequences. For patients with intracranial metastasis, we measured enhancement degree and CNR_{lesion/parenchyma} of the lesion. The overall image quality, motion artifact, gray-white matter discrimination and enhancing lesion conspicuity were analyzed. Both MPRAGE and CS-VIBE showed similar performance in diagnosing intracranial metastasis. Overall image quality of CS-VIBE was better with less motion artifact; however conventional MPRAGE was superior in enhancing lesion conspicuity. Overall, the SNR and CNR of conventional MPRAGE were higher than those of CS-VIBE. For 30 enhancing intracranial metastatic lesions, MPRAGE showed a lower CNR (p = 0.02) and contrast ratio (p = 0.03). MPRAGE and CS-VIBE were preferred in 11.6 and 13.4% of cases, respectively. In comparison with conventional MPRAGE, CS-VIBE achieved comparable image quality and visualization, with the scan time being half of that of MPRAGE.

Photon-counting detector coronary CT angiography: impact of virtual monoenergetic imaging and iterative reconstruction on image quality

OBJECTIVES

To assess the impact of low kilo-electronvolt (keV) virtual monoenergetic image (VMI) energies and iterative reconstruction on image quality of clinical photon-counting detector coronary CT angiography (CCTA).

METHODS

CCTA with PCD-CT (prospective ECG-triggering, 120 kVp, automatic tube current modulation) was performed in a high-end cardiovascular phantom with dynamic flow, pulsatile heart motion, and including different calcified plaques with various stenosis grades and in 10 consecutive patients. VMI at 40,50,60 and 70 keV were reconstructed without (QIR-off) and with all quantum iterative reconstruction (QIR) levels (QIR-1 to 4). In the phantom, noise power spectrum, vessel attenuation, contrast-to-noise-ratio (CNR), and vessel sharpness were measured. Two readers graded stenoses in the phantom and graded overall image quality, subjective noise, vessel sharpness, vascular contrast, and coronary artery plaque delineation on 5-point Likert scales in patients.

RESULTS

In the phantom, noise texture was only slightly affected by keV and QIR while noise increased by 69% from 70 keV QIR-4 to 40 keV QIR-off. Reconstructions at 40 keV QIR-4 exhibited the highest CNR (46.1 ± 1.8), vessel sharpness (425 ± 42 ∆HU/mm), and vessel attenuation (1098 ± 14 HU). Stenosis measurements were not affected by keV or QIR level (p > 0.12) with an average error of 3%/6% for reader 1/reader 2, respectively. In patients, across all subjective categories and both readers, 40 keV QIR-3 and QIR-4 images received the best scores (p < 0.001).

CONCLUSION

Forty keV VMI with QIR-4 significantly improved image quality of CCTA with PCD-CT.

ADVANCES IN KNOWLEDGE

PCD-CT at 40 keV and QIR-4 improves image quality of CCTA.

Time-of-Flight Intracranial MRA at 3 T versus 5 T versus 7 T: Visualization of Distal Small Cerebral Arteries

Background Three-dimensional (3D) time-of-flight (TOF) MR angiography (MRA) at 7 T has been reported to have high image quality for visualizing small perforating vessels. However, B₁ inhomogeneity and more physiologic considerations limit its applications. Angiography at 5 T may provide another choice for intracranial vascular imaging. Purpose To evaluate the image quality and cerebrovascular visualization of 5-T 3D TOF MRA for visualizing intracranial small branch arteries. Materials and Methods Participants (healthy volunteers or participants with a history of ischemic stroke undergoing intracranial CT angiography or MRA for identifying steno-occlusive disease) were prospectively included from September 2021 to November 2021. Each participant underwent 3-T, 5-T, and 7-T 3D TOF MRA with use of customized MR protocols within 48 hours. Radiologist scoring from 0 (invisible) to 3 (excellent) and quantitative assessment were obtained to evaluate the image quality. The Friedman test was used for comparison of characteristics derived from 3 T, 5 T, and 7 T. Results A total of 12 participants (mean age ± SD, 38 years ± 9; nine men) were included. Visualizations of the distal arteries and small vessels at 5-T TOF MRA were significantly higher than those at 3 T (median score: 3.0 vs 2.0, all P < .001 for distal segments and lenticulostriate artery; median score: 2.0 vs 0, P < .001 for pontine artery). The total length of small vessel branches detected at 5 T was larger than that at 3 T (5.1 m ± 0.7 vs 1.9 m ± 0.4; P < .001). However, there was no evidence of a significant difference compared with 7 T in either the depiction of distal segments and small vessel branches (average median score, 2.5; all P > .05) or the quantitative measurements (total length, 5.6 m ± 0.5; P = .41). Conclusion Three-dimensional time-of-flight MR angiography at 5 T presented the capability to provide superior visualization of distal large arteries and small vessel branches (in terms of subjective and quantitative assessment) to 3 T and had image quality similar to 7 T. © RSNA, 2022 Online supplemental material is available for this article. An earlier incorrect version appeared online. This article was corrected on September 14, 2022.

Contrast-Enhanced Abdominal CT with Clinical Photon-Counting Detector CT: Assessment of Image Quality and Comparison with Energy-Integrating Detector CT

RATIONALE AND OBJECTIVES

To determine quantitative and qualitative image quality of contrast-enhanced abdominal photon-counting detector CT (PCD-CT) compared to energy-integrating detector CT (EID-CT) in the same patients.

MATERIAL AND METHODS

Thirty-nine patients (mean age 63 ± 10 years, 10 females, mean BMI 26.0 ± 5.7 kg/m²) were retrospectively included who underwent clinically indicated, contrast-enhanced abdominal CT in portal-venous phase with first-generation dual-source PCD-CT and who underwent previous abdominal CT with EID-CT. For both scan, same contrast media protocol was used. PCD-CT was performed in QuantumPlus mode (obtaining full spectral information) at 120kVp. EID-CT was performed using automated tube voltage selection (reference tube voltage 100kVp). In PCD-CT, virtual monoenergetic images (VMI) were reconstructed in 10keV intervals (40-90 keV). Tube current-time product in PCD-CT was modified in each patient to obtain same volume CT-dose-index (CTDI_vol) as with EID-CT. Attenuation of organs and vascular structures were measured, noise quantified, and contrast-to-noise ratio (CNR) calculated. Two independent, blinded radiologists assessed subjective image quality using a 5-point Likert scale (overall image quality, image noise, contrast, and liver lesion conspicuity).

RESULTS

Median time interval between the scan was 12 months. BMI (p = 0.905) and CTDI_vol (p = 0.984) were similar between scans. CNR_parenchymal and CNR_vascular of VMI from PCD-CT at 40 and 50keV were significantly higher than EID-CT (all, p < 0.05). Overall, inter-reader agreement for all subjective image quality readings was substantial (Krippendorff's alpha = 0.773). Overall image quality of VMI was rated similar at 50 and 60 keV compared to EID-CT (all, p > 0.05). Subjective image noise was significantly higher at 40-50 keV, contrast significantly higher at 40-60 keV (all, p < 0.05). Lesion conspicuity was rated similar on all images.

CONCLUSION

Our intra-individual analysis of abdominal PCD-CT indicates that VMI at 50 keV shows significantly higher CNR at similar subjective image quality as compared to EID-CT at identical radiation dose.

Evaluation of an Ultra-Short MRI Protocol for Cerebral Staging Examinations in Melanoma Patients

PURPOSE

 Due to its high sensitivity and lack of radiation, MRI is often used to stage cerebral tumors in patients. In contrast, the relatively long examination times and the limited availability of MRI slots at the clinic might delay these examinations. The aim of this study was to compare an ultra-short MRI protocol with the routinely used standard protocol.

MATERIALS AND METHODS

 Cerebral MRI of 147 patients with malignant melanoma were evaluated retrospectively, whereby only two sequences (FLAIR images and contrast-enhanced T1 MPR images) were evaluated in one group and images from the whole examination were available for the second group, including five sequences (DWI, T2 TSE, FLAIR, native and contrast-enhanced T1 TSE, and contrast-enhanced T1 MPR). The results of the two groups were compared and tested to determine whether the ultra-short approach was inferior to the full examination.

RESULTS

 13.6 % of the patients had cerebral metastases. Overall, 73 metastases were detected: 60 were located supratentorially and 13 infratentorially. Concerning the detection of cerebral metastases, the ultra-short MRI examination, involving only a FLAIR and a contrast-enhanced T1 MPR sequence, was not inferior to the full MRI protocol in general (p = 0.017) and separated by location for supratentorial (p = 0.026) and infratentorial (p = 0.001) metastases.

CONCLUSION

 For staging purposes, a focused, ultra-short MRI protocol is not inferior to a standard MRI examination. This might open up opportunities for faster staging processes and a more efficient use of the often-restricted MRI capacities.

KEY POINTS

  · Short MRI protocols for cerebral staging are not inferior to standard examinations.. · Contrast-enhanced images represent the centerpiece of an ultra-short MRI protocol.. · Short MRI protocols might enable a more efficient use of restricted resources..

CITATION FORMAT

· Peters S, Gärtner F, Austein F et al. Evaluation of an Ultra-Short MRI Protocol for Cerebral Staging Examinations in Melanoma Patients. Fortschr Röntgenstr 2021; DOI: 10.1055/a-1669-9408.

Contrast-Enhanced T1-Weighted Head and Neck MRI: Prospective Intraindividual Image Quality Comparison of Spiral GRE, Cartesian GRE, and Cartesian TSE Sequences

BACKGROUND. Sequences with noncartesian k-space sampling may improve image quality of head and neck MRI. OBJECTIVE. The purpose of this study was to compare intraindividually the image quality of a spiral gradient-recalled echo (GRE) sequence and conventional cartesian GRE and cartesian turbo spin-echo (TSE) sequences for contrast-enhanced T1-weighted head and neck MRI. METHODS. This prospective study included patients referred for contrast-enhanced head and neck MRI from August 2020 to May 2021. Patients underwent 1.5-T MRI including contrast-enhanced spiral GRE (2 minutes 28 seconds), cartesian GRE (4 minutes 27 seconds), and cartesian TSE (3 minutes 41 seconds) sequences, acquired in rotating order across patients. Three radiologists independently assessed image quality measures, including conspicuity of prespecified lesions, using 5-point Likert scales. One reader measured maximal extent of dental material artifact and contrast-to-noise ratio (CNR). RESULTS. Thirty-one patients (13 men, 18 women; mean age, 63.8 years) were enrolled. Nineteen patients had a focal lesion; 22 had dental material. Interreader agreement for image quality measures was substantial to excellent (Krippendorff alpha, 0.681-1.000). Scores for overall image quality (whole head and neck, neck only, and head only), pulsation artifact, muscular contour delineation, vessel contour delineation, motion artifact, and differentiation between mucosa and pharyngeal muscles were significantly better for spiral GRE than for cartesian GRE and cartesian TSE for all readers (p < .05). Scores for lesion conspicuity (whole head and neck, neck only, and head only), quality of fat suppression, flow artifact, and foldover artifact were not significantly different between spiral GRE and the cartesian sequences for any reader (p > .05). Dental material artifact scores were significantly worse for spiral GRE than the other sequences for all readers (p < .05). The mean maximum extent of dental material artifact was 39.6 ± 25.5 (SD) mm for spiral GRE, 35.6 ± 24.3 mm for cartesian GRE, and 29.6 ± 21.4 mm for cartesian TSE; the mean CNR was 221.1 ± 94.5 for spiral GRE, 151.8 ± 85.7 for cartesian GRE, and 153.0 ± 63.2 for cartesian TSE (p < .001 between spiral GRE and other sequences for both measures). CONCLUSION. Three-dimensional spiral GRE improves subjective image quality and CNR of head and neck MRI with shorter scan time versus cartesian sequences, though it exhibits larger dental material artifact. CLINICAL IMPACT. A spiral sequence may help overcome certain challenges of conventional cartesian sequences for head and neck MRI.

Spiral 2D T2-Weighted TSE Brain MR Imaging: Initial Clinical Experience

BACKGROUND AND PURPOSE

Spiral MR imaging may enable improved image quality and higher scan speeds than Cartesian trajectories. We sought to compare a novel spiral 2D T2-weighted TSE sequence with a conventional Cartesian and an artifact-robust, non-Cartesian sequence named MultiVane for routine clinical brain MR imaging.

MATERIALS AND METHODS

Thirty-one patients were scanned with all 3 sequences (Cartesian, 4 minutes 14 seconds; MultiVane, 2 minutes 49 seconds; spiral, 2 minutes 12 seconds) on a standard clinical 1.5T MR scanner. Three readers described the presence and location of abnormalities and lesions and graded images qualitatively in terms of overall image quality, the presence of motion and pulsation artifacts, gray-white matter differentiation, lesion conspicuity, and subjective preference. Image quality was objectivized by measuring the SNR and the coefficients of variation for CSF, GM, and WM.

RESULTS

Spiral achieved a scan time reduction of 51.9% and 21.9% compared with Cartesian and MultiVane, respectively. The number and location of lesions were identical among all sequences. As for the qualitative analysis, interreader agreement was high (Krippendorff α > .75). Spiral and MultiVane both outperformed the Cartesian sequence in terms of overall image quality, the presence of motion artifacts, and subjective preference (P < .001). In terms of the presence of pulsation artifacts, gray-white matter differentiation, and lesion conspicuity, all 3 sequences performed similarly well (P > .15). Spiral and MultiVane outperformed the Cartesian sequence in coefficient of variation WM and SNR (P < .01).

CONCLUSIONS

Spiral 2D T2WI TSE is feasible for routine structural brain MR imaging and offers high-quality, artifact-robust brain imaging in short scan times.

Qualitative and Quantitative Analysis of a Spiral Gradient Echo Sequence for Contrast-Enhanced Fat-Suppressed T1-Weighted Spine Magnetic Resonance Imaging

OBJECTIVES

Pulse sequences with non-Cartesian k-space sampling enable improved imaging in anatomical areas with high degrees of motion artifacts. We analyzed a novel spiral 3-dimensional (3D) gradient echo (GRE) magnetic resonance imaging (MRI) sequence ("spiral," 114.7 ± 11 seconds) and compared it with a radial 3D GRE ("vane," 216.7 ± 2 seconds) and a conventional Cartesian 2D turbo spin echo (TSE) sequence ("TSE," 266.7 ± 82 seconds) for contrast-enhanced fat-suppressed T1-weighted spine imaging.

MATERIALS AND METHODS

Forty consecutive patients referred for contrast-enhanced MRI were prospectively scanned with all 3 sequences. A qualitative analysis was performed by 3 readers using 4- or 5-point Likert scales to independently grade images in terms of overall image quality, occurrence of artifacts, lesion conspicuity, and conspicuity of nerve roots. The numbers of visible nerve roots per sequence and patient were counted in consensus. Coefficient of variation measurements were performed for the paravertebral musculature (CVPM) and the spinal cord (CVSC).

RESULTS

Spiral (median [interquartile range], 5 [4-5]) exhibited improved overall image quality in comparison to TSE (3 [3-4]) and vane (4 [4-5]; both P < 0.001). Vane surpassed TSE in terms of overall image quality (P < 0.001). Spiral (4 [3.75-4]) and vane (3.5 [3-4]) presented with less artifacts than TSE (3 [2.75-3.25]; both P < 0.001). Spiral (4 [4-5]) outperformed vane (4 [3-5]; P = 0.01) and TSE (4 [3-4]; P = 0.04) in terms of lesion conspicuity. Conspicuity of nerve roots was superior on spiral (3 [3-4]) and vane (4 [3-4]) when compared with TSE (1.5 [1-2]; both P < 0.001). Readers discerned significantly more nerve roots on spiral (4 [2.75-8]) and vane (4 [3.75-7.25]) images when compared with TSE (2 [0-4]; both P < 0.001). Interreader agreement ranged from moderate (α = 0.639) to almost perfect (α = 0.967). CVPM and CVSC were significantly lower on spiral as compared with vane and TSE (P < 0.001, P = 0.04). Vane exhibited lower CVPM and CVSC than TSE (P < 0.001, P = 0.01).

CONCLUSIONS

A novel spiral 3D GRE sequence improves contrast-enhanced fat-suppressed T1-weighted spinal imaging qualitatively and quantitatively in comparison with a conventional Cartesian 2D TSE sequence and to a lesser extent with a radial 3D GRE sequence at shorter scan times.

Wave-controlled aliasing in parallel imaging magnetization-prepared gradient echo (wave-CAIPI MPRAGE) accelerates speed for pediatric brain MRI with comparable diagnostic performance

We aimed to compare accelerated post-contrast magnetization-prepared rapid gradient-echo (MPRAGE) using wave-controlled aliasing in parallel imaging (wave-CAIPI) with conventional MPRAGE as a reliable method to diagnose intracranial lesions in pediatric patients. A total of 23 consecutive pediatric patients who underwent post-contrast wave-CAIPI and conventional MPRAGE (scan time: 2 min 39 s vs. 5 min 46 s) were retrospectively evaluated. Two radiologists independently assessed each image for the presence of intracranial lesions. Quantitative [contrast-to-noise ratio (CNR), contrast rate (CR), and signal-to-noise ratio (SNR)] and qualitative parameters (overall image quality, gray-white matter differentiation, demarcation of basal ganglia and sulci, and motion artifacts) were also surveyed. Wave-CAIPI MPRAGE and conventional MPRAGE detected enhancing and non-enhancing intracranial lesions with 100% agreement. Although wave-CAIPI MPRAGE had a lower SNR (all p < 0.05) and overall image quality (overall analysis, p = 0.02) compared to conventional MPRAGE, other quantitative (CNR and CR) and qualitative parameters (gray-white differentiation, demarcation of basal ganglia and sulci, and motion artifacts) were comparable in the pooled analysis and between both observers (all p > 0.05). Wave-CAIPI MPRAGE was a reliable method for diagnosing intracranial lesions in pediatric patients as conventional MPRAGE at half the scan time.

Spiral 3-Dimensional T1-Weighted Turbo Field Echo: Increased Speed for Magnetization-Prepared Gradient Echo Brain Magnetic Resonance Imaging

OBJECTIVES

Spiral magnetic resonance imaging acquisition may enable improved image quality and higher scan speeds than Cartesian trajectories. We tested the performance of four 3D T1-weighted (T1w) TFE sequences (magnetization-prepared gradient echo magnetic resonance sequence) with isotropic spatial resolution for brain imaging at 1.5 T in a clinical patient cohort based on qualitative and quantitative image quality metrics. Two prototypical spiral TFE sequences (spiral 1.0 and spiral 0.85) and a Cartesian compressed sensing technology accelerated TFE sequence (CS 2.5; acceleration factor of 2.5) were compared with a conventional (reference standard) Cartesian parallel imaging accelerated TFE sequence (SENSE; acceleration factor of 1.8).

MATERIALS AND METHODS

The SENSE (5:52 minutes), CS 2.5 (3:17 minutes), and spiral 1.0 (2:16 minutes) sequences all had identical spatial resolutions (1.0 mm). The spiral 0.85 (3:47 minutes) had a higher spatial resolution (0.85 mm). The 4 TFE sequences were acquired in 41 patients (20 with and 21 without contrast media). Three readers rated qualitative image quality (12 categories) and selected their preferred sequence for each patient. Two readers performed quantitative analysis whereby 6 metrics were derived: contrast-to-noise ratio for white and gray matter (CNRWM/GM), contrast ratio for gray matter-CSF (CRGM/CSF), and white matter-CSF (CRWM/CSF); and coefficient of variations for gray matter (CVGM), white matter (CVWM), and CSF (CVCSF). Friedman tests with post hoc Nemenyi tests, exact binomial tests, analysis of variance with post hoc Dunnett tests, and Krippendorff alphas were computed.

RESULTS

Concerning qualitative analysis, the CS 2.5 sequence significantly outperformed the SENSE in 4/1 (with/without contrast) categories, whereas the spiral 1.0 and spiral 0.85 showed significantly improved scores in 10/9and 7/7 categories, respectively (P's < 0.001-0.039). The spiral 1.0 was most frequently selected as the preferred sequence (reader 1, 10/15 times; reader 2, 9/12 times; reader 3, 11/13times [with/without contrast]). Interreader agreement ranged from substantial to almost perfect (alpha = 0.615-0.997). Concerning quantitative analysis, compared with the SENSE, the CS 2.5 had significantly better scores in 2 categories (CVWM, CVCSF) and worse scores in 2 categories (CRGM/CSF, CRWM/CSF), the spiral 1.0 had significantly improved scores in 4 categories (CNRWM/GM, CRGM/CSF, CRWM/CSF, CVWM), and the spiral 0.85 had significantly better scores in 2 categories (CRGM/CSF, CRWM/CSF).

CONCLUSIONS

Spiral T1w TFE sequences may deliver high-quality clinical brain imaging, thus matching the performance of conventional parallel imaging accelerated T1w TFEs. Imaging can be performed at scan times as short as 2:16 minutes per sequence (61.4% scan time reduction compared with SENSE). Optionally, spiral imaging enables increased spatial resolution while maintaining the scan time of a Cartesian-based acquisition schema.

Diffusion-weighted MRI of ischemic stroke at 3T: Value of synthetic b-values

OBJECTIVES

Diffusion-weighted imaging (DWI) plays a crucial role in the diagnosis of ischemic stroke. We assessed the value of computed and acquired high b-value DWI in comparison with conventional b = 1000 s mm^-2 DWI for ischemic stroke at 3T.

METHODS

We included 36 patients with acute ischemic stroke who presented with diffusion abnormalities on DWI performed within 24 h of symptom onset. B-values of 0, 500, 1000 and 2000 s mm^-2 were acquired. Synthetic images with b-values of 1000, 1500, 2000 and 2500 s mm^-2 were computed. Two readers compared synthetic (syn) and acquired (acq) b = 2000 s mm^-2 images with acquired b = 1000 s mm^-2 images in terms of lesion detection rate, image quality, presence of uncertain hyperintensities and lesion conspicuity. Readers also selected their preferred b-value. Contrast ratio (CR) measurements were performed. Non-parametrical statistical tests and weighted Cohens' κ tests were computed.

RESULTS

Syn1000 and syn1500 matched acq1000 images in terms of lesion detection rate, image quality and presence of uncertain hyperintensities but presented with significantly improved lesion conspicuity (p < 0.01) and were frequently selected as preferred b-values. Acq2000 images exhibited a similar lesion detection rate and improved lesion conspicuity (p < 0.01) but worse image quality (p < 0.01) than acq1000 images. Syn2000 and syn2500 images performed significantly worse (p < 0.01) than acq1000 images in most or all categories. CR significantly increased with increasing b-values.

CONCLUSION

Synthetic images at b = 1000 and 1500 s mm^-2 and acquired DWI images at b = 2000 s mm^-2 may be of clinical value due to improved lesion conspicuity.

ADVANCES IN KNOWLEDGE

Synthetic b-values enable improved lesion conspicuity for DWI of ischemic stroke.

Acceleration of Brain TOF-MRA with Compressed Sensitivity Encoding: A Multicenter Clinical Study

BACKGROUND AND PURPOSE

The clinical practice of three-dimensional TOF-MRA, despite its capability in brain artery assessment, has been hampered by the relatively long scan time, while recent developments in fast imaging techniques with random undersampling has shed light on an improved balance between image quality and imaging speed. Our aim was to evaluate the effectiveness of TOF-MRA accelerated by compressed sensitivity encoding and to identify the optimal acceleration factors for routine clinical use.

MATERIALS AND METHODS

One hundred subjects, enrolled at 5 centers, underwent 8 brain TOF-MRA sequences: 5 sequences using compressed sensitivity encoding with acceleration factors of 2, 4, 6, 8, and 10 (CS2, CS4, CS6, CS8, and CS10), 2 using sensitivity encoding with factors of 2 and 4 (SF2 and SF4), and 1 without acceleration as a reference sequence (RS). Five large arteries, 6 medium arteries, and 6 small arteries were evaluated quantitatively (reconstructed signal intensity, structural similarity, contrast ratio) and qualitatively (scores on arteries, artifacts, overall image quality, and diagnostic confidence for aneurysm and stenosis). Comparisons were performed among the 8 sequences.

RESULTS

The quantitative measurements showed that the reconstructed signal intensities of the assessed arteries and the structural similarity consistently decreased as the compressed sensitivity encoding acceleration factor increased, and no significant difference was found for the contrast ratios in pair-wise comparisons among SF2, CS2, and CS4. Qualitative evaluations showed no significant difference in pair-wise comparisons among RS, SF2, and CS2 (P > .05). The visualization of all the assessed arteries was acceptable for CS2 and CS4, while 2 small arteries in images of CS6 were not reliably displayed, and the visualization of large arteries was acceptable in images of CS8 and CS10.

CONCLUSIONS

CS4 is recommended for routine brain TOF-MRA with balanced image quality and acquisition time; CS6, for examinations when small arteries are not evaluated; and CS10, for fast visualization of large arteries.

Novel Ultrafast Spiral Head MR Angiography Compared to Standard MR and CT Angiography

BACKGROUND AND PURPOSE

Intracranial vessel imaging by time-of-flight MR angiography (TOF-MRA) is one of the most frequently performed investigations in clinical neuroradiology. Particularly in the acute setting, fast imaging is needed for diagnostics, with a sequence ideally depicting even small vessels. The purpose of this study was to compare image and diagnostic quality of a novel ultrashort TOF-MRA sequence accelerated by spiral imaging (TOF-Spiral-short) to a standard TOF-MRA sequence accelerated by compressed sensing (TOF-CS) and to CT angiography (CTA).

METHODS

Forty-one patients (36.6% showing vessel pathologies) who had undergone TOF-CS (acquisition duration: 4 minutes 8 seconds), TOF-Spiral-short (acquisition duration: 51 seconds; spiral imaging [accelerating factor 1.3], decreased field of view [accelerating factor 1.2], and increased voxel size [accelerating factor 3.3]), and CTA were retrospectively evaluated. Assessment of image quality, diagnostic confidence, and quantification of stenosis or aneurysm diameter were performed by two readers.

RESULTS

Image quality at the skull base was slightly reduced with TOF-Spiral-short compared to CTA and TOF-CS (P < .05). Delineation of small intracranial vessels was improved by TOF-Spiral-short compared to CTA (P < .0001). In TOF-Spiral-short, diagnostic confidence was not reduced compared to TOF-CS in patients with vessel pathologies. We observed no significant difference in quantitative pathology assessment between TOF-Spiral-short and the other two modalities. TOF-Spiral-short enabled the correct identification of all vessel pathologies.

CONCLUSIONS

Accelerating TOF-MRA of brain-feeding arteries by a novel ultrashort spiral imaging sequence shows adequate image quality and sufficient diagnostic performance. Thus, TOF-Spiral-short holds potential for fast and reliable diagnostics of vessel pathologies, particularly in the acute setting.

Clinical feasibility of ultrafast intracranial vessel imaging with non-Cartesian spiral 3D time-of-flight MR angiography at 1.5T: An intra-individual comparison study

Objectives

Non-Cartesian Spiral readout can be implemented in 3D Time-of-flight (TOF) MR angiography (MRA) with short acquisition times. In this intra-individual comparison study we evaluated the clinical feasibility of Spiral TOF MRA in comparison with compressed sensing accelerated TOF MRA at 1.5T for intracranial vessel imaging as it has yet to be determined.

Materials and methods

Forty-four consecutive patients with suspected intracranial vascular disease were imaged with two Spiral 3D TOFs (Spiral, 0.82x0.82x1.2 mm³, 01:32 min; Spiral 0.8, 0.8x0.8x0.8 mm^3, 02:12 min) and a Compressed SENSE accelerated 3D TOF (CS 3.5, 0.82x0.82x1.2 mm³, 03:06 min) at 1.5T. Two neuroradiologists assessed qualitative (visualization of central and peripheral vessels) and quantitative image quality (Contrast Ratio, CR) and performed lesion and variation assessment for all three TOFs in each patient. After the rating process, the readers were questioned and representative cases were reinspected in a non-blinded fashion. For statistical analysis, the Friedman and Nemenyi post-hoc test, Kendall W tests, repeated measure ANOVA and weighted Cohen's Kappa tests were used.

Results

The Spiral and Spiral 0.8 outperformed the CS 3.5 in terms of peripheral image quality (p<0.001) and performed equally well in terms of central image quality (p>0.05). The readers noted slight differences in the appearance of maximum intensity projection images. A good to high degree of interstudy agreement between the three TOFs was observed for lesion and variation assessment (W = 0.638, p<0.001 –W = 1, p<0.001). CR values did not differ significantly between the three TOFs (p = 0.534). Interreader agreement ranged from good (K = 0.638) to excellent (K = 1).

Conclusions

Compared to the CS 3.5, both the Spiral and Spiral 0.8 exhibited comparable or better image quality and comparable diagnostic performance at much shorter acquisition times.