Ungated nonenhanced radial quiescent interval slice-selective (QISS) magnetic resonance angiography of the neck: Evaluation of image quality

Highly compressed SENSE accelerated relaxation-enhanced angiography without contrast and triggering (REACT) for fast non-contrast enhanced magnetic resonance angiography of the neck: Clinical evaluation in patients with acute ischemic stroke at 3 tesla

BACKGROUND AND PURPOSE

Long acquisition times limit the feasibility of established non-contrast-enhanced MRA (non-CE-MRA) techniques. The purpose of this study was to evaluate a highly accelerated flow-independent sequence (Relaxation-Enhanced Angiography without Contrast and Triggering [REACT]) for imaging of the extracranial arteries in acute ischemic stroke (AIS).

MATERIALS AND METHODS

Compressed SENSE (CS) accelerated (factor 7) 3D isotropic REACT (fixed scan time: 01:22 min, reconstructed voxel size 0.625 × 0.625 × 0.75 mm3) and CE-MRA (CS factor 6, scan time: 1:08 min, reconstructed voxel size 0.5 mm3) were acquired in 76 AIS patients (69.4 ± 14.3 years, 33 females) at 3 Tesla. Two radiologists assessed scans for the presence of internal carotid artery (ICA) stenosis and stated their diagnostic confidence using a 5-point scale (5 = excellent). Vessel quality of cervical arteries as well as the impact of artifacts and image noise were scored on 5-point scales (5 = excellent/none). Apparent signal- and contrast-to-noise ratios (aSNR/aCNR) were measured for the common carotid artery (CCA) and ICA (C1-segment).

RESULTS

REACT provided a sensitivity of 88.5% and specificity of 100% for clinically relevant (≥50%) ICA stenosis with substantial concordance to CE-MRA regarding stenosis grading (Cohen's kappa 0.778) and similar diagnostic confidence (REACT: mean 4.5 ± 0.4 vs. CE-MRA: 4.5 ± 0.6; P = 0.674). Presence of artifacts (3.6 ± 0.5 vs. 3.5 ± 0.7; P = 0.985) and vessel quality (all segments: 3.6 ± 0.7 vs. 3.8 ± 0.7; P = 0.004) were comparable between both techniques with REACT showing higher scores at the CCA (4.3 ± 0.6 vs. 3.8 ± 0.9; P < 0.001) and CE-MRA at V2- (3.3 ± 0.5 vs. 3.9 ± 0.8; P < 0.001) and V3-segments (3.3 ± 0.5 vs. 4.0 ± 0.8; P < 0.001). For all vessels, REACT showed a lower impact of image noise (3.8 ± 0.6 vs. 3.6 ± 0.7; P = 0.024) while yielding higher aSNR (52.5 ± 15.1 vs. 37.9 ± 12.5; P < 0.001) and aCNR (49.4 ± 15.0 vs. 34.7 ± 12.3; P < 0.001) for all vessels combined.

CONCLUSIONS

In patients with acute ischemic stroke, highly accelerated REACT provides an accurate detection of ICA stenosis with vessel quality and scan time comparable to CE-MRA.

Imaging of the extracranial internal carotid artery in acute ischemic stroke: assessment of stenosis, plaques, and image quality using relaxation-enhanced angiography without contrast and triggering (REACT)

BACKGROUND

In stroke magnetic resonance imaging (MRI), contrast-enhanced magnetic resonance angiography (CE-MRA) is the clinical standard to depict extracranial arteries but native MRA techniques are of increased interest to facilitate clinical practice. The purpose of this study was to assess the detection of extracranial internal carotid artery (ICA) stenosis and plaques as well as the image quality of cervical carotid arteries between a novel flow-independent relaxation-enhanced angiography without contrast and triggering (REACT) sequence and CE-MRA in acute ischemic stroke (AIS).

METHODS

In this retrospective, single-center study, 105 consecutive patients (65.27±18.74 years, 63 males) were included, who received a standard stroke protocol at 3T in clinical routine including Compressed SENSE (CS) accelerated (factor 4) 3D isotropic REACT (fixed scan time: 02:46 min) and CS accelerated (factor 6) 3D isotropic CE-MRA. Three radiologists independently assessed scans for the presence of extracranial ICA stenosis and plaques (including hyper-/hypointense signal) with concomitant diagnostic confidence using 3-point scales (3= excellent). Vessel quality, artifacts, and image noise of extracranial carotid arteries were subjectively scored on 5-point scales (5= excellent/none). Wilcoxon tests were used for statistical comparison.

RESULTS

Considering CE-MRA as the standard of reference, REACT provided a sensitivity of 89.8% and specificity of 95.2% for any and of 93.5% and 95.8% for clinically relevant (≥50%) extracranial ICA stenosis and yielded a to CE-MRA comparable diagnostic confidence [mean ± standard deviation (SD), median (interquartile range): 2.8±0.5, 3 (3-3) vs. 2.7±0.5, 3 (2-3), P=0.03]. Using REACT, readers detected more plaques overall (n=57.3 vs. 47.7, P<0.001) and plaques of hyperintense signal (n=12.3 vs. 5.7, P=0.02) with higher diagnostic confidence [2.8±0.5, 3 (3-3) vs. 2.6±0.7, 3 (2-3), P<0.001] than CE-MRA. After analyzing a total of 1,260 segments, the vessel quality of all segments combined [4.61±0.66 vs. 4.58±0.68, 5 (4-5) vs. 5 (4-5), P=0.0299] and artifacts [4.51±0.70 vs. 4.44±0.73, 5 (4-5) vs. 5 (4-5), P>0.05] were comparable between the sequences with REACT showing a lower image noise [4.43±0.67 vs. 4.25±0.71, 5 (4-5) vs. 4 (4-5), P<0.001].

CONCLUSIONS

Without the use of gadolinium-based contrast agents or triggering, REACT provides a high sensitivity and specificity for extracranial ICA stenosis and a potential improved depiction of adjacent plaques while yielding to CE-MRA comparable vessel quality in a large patient cohort with AIS.

Predictability and image quality of low-dose cone-beam computed tomography in computer-guided implantology: An experimental study

OBJECTIVES

To investigate the predictability and image quality of low-dose cone-beam computed tomography (LD-CBCT) in computer-guided implantology.

METHODS

Pig cadaver mandibles were imaged using high-definition CBCT (HD-CBCT) and LD-CBCT (HD-CBCT: 85 kV, 6 mA, 14.2 s, 767 frames, 1184 mGycm², voxel size 80 µm, effective dose 231 µSv; LD-CBCT: 85 kV, 10 mA, 2.1 s, 384 frames, 84 mGycm², voxel size 160 µm, effective dose 16 µSv; Orthophos SL, Dentsply Sirona, Bensheim, Germany). Digital impressions were taken using intraoral scanning (IOS; Omnicam, Dentsply Sirona). Data of CBCT modalities and IOS were aligned. Forty-eight implants were planned virtually (24 implants per modality; Bone Level 4.1 × 10 mm; Straumann AG, Basel, Switzerland). Implants were inserted using templates by initial pilot drilling ("partially-guided implantation"). Implant positions were recorded using IOS. Geometric deviations between planned and definitive positions were assessed regarding implant apex, entry-point and angle. CBCT image quality was evaluated by raters twice on a four point scale. The results were exploratively compared (linear models, Mann-Whitney-U tests).

RESULTS

Regarding implant apex, deviations were greater for LD-CBCT (mean 3.0±1.2 mm), as compared to HD-CBCT (mean 2.3±1.1 mm). For entry-point, no distinct difference was detected with a mean deviation of 1.4±0.9 mm in LD-CBCT, and 1.7±0.6 mm in HD-CBCT. Regarding angle, deviations were greater for LD-CBCT (mean 13.2±6.3°), as compared to HD-CBCT (mean 9.2±5.3°). The image quality of HD-CBCT provided to be better (mean 2.7±0.6) than that of LD-CBCT (mean 2.5±0.6).

CONCLUSIONS

Within the partially-guided approach, the results underline the potential of LD-CBCT alternatively to HD-CBCT for computer-guided implantology. Advantages of HD-CBCT need to be balanced against the higher radiation dose.

High-resolution, non-contrast-enhanced magnetic resonance angiography of the wrist, hand and digital arteries using optimized implementation of Cartesian quiescent interval slice selective (QISS) at 1.5 T

PURPOSE

Non-contrast-enhanced (CE) magnetic resonance angiography (MRA) techniques are of considerable interest for diagnosing vascular diseases in the upper extremities owing to the possibility of repeated examinations, sufficient coverage of the measurement volume, and because possible side effects of administering iodine- or gadolinium-based contrast agents and radiation exposure can be avoided. The aim of this study was to investigate the feasibility of an optimized electrocardiogram (ECG) triggered Cartesian quiescent interval slice selective (QISS) technique for MRA of hand arteries.

MATERIAL AND METHODS

Both hands of 20 healthy volunteers (HVs) were examined using an optimized QISS-MRA pulse sequence at 1.5 Tesla. The wrist and hand arterial trees were divided into 36 segments. Cross-sectional areas (CSA) of all arterial segments were measured. For the technical evaluation of the pulse sequence, the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were computed and six imaging artifacts were graded. Two experienced observers used an ordinal scoring system to assess the image quality of each arterial segment. Interobserver agreement was determined.

RESULTS

The median CSA was 7.3 mm2 in the ulnar and radial artery, 3.2 mm2 in the four common digital arteries, and 1.5 mm2 in five proper digital arteries. The median SNR and CNR of the third common proper arteries were 45.9 and 20.3, respectively. None of the arterial segments were contaminated by venous enhancement. The image quality of arterial segments for both hands was considered as diagnostic in 87.2% of all 1440 segments. An interobserver agreement of 0.67 for both hands was determined for image quality of arterial segments using a five-grade scoring system. Optimized QISS-MRA allows as the first MRA technique the classification of superficial palmar arch (SPA) and deep palmar arch (DPA) variants. 5 new SPA and 6 new DPA variants could be classified using QISS-MRA in comparison with previous studies using CE computed tomography angiography and using fixed cadaver hands.

CONCLUSIONS

By using this optimized 2D Cartesian QISS-MRA protocol, contrast agent-free angiography of the wrist and hand arteries provided a high in-plane spatial resolution and an excellent visualization of small digital arteries.

Relaxation-Enhanced Angiography Without Contrast and Triggering (REACT) for Fast Imaging of Extracranial Arteries in Acute Ischemic Stroke at 3 T

Purpose

To evaluate a novel flow-independent 3D isotropic REACT sequence compared with CE-MRA for the imaging of extracranial arteries in acute ischemic stroke (AIS).

Methods

This was a retrospective study of 35 patients who underwent a stroke protocol at 3 T including REACT (fixed scan time: 2:46 min) and CE-MRA of the extracranial arteries. Three radiologists evaluated scans regarding vessel delineation, signal, and contrast and assessed overall image noise and artifacts using 5-point scales (5: excellent delineation/no artifacts). Apparent signal- and contrast-to-noise ratios (aSNR/aCNR) were measured for the common carotid artery (CCA), internal carotid artery (ICA, C1 segment), and vertebral artery (V2 segment). Two radiologists graded the degree of proximal ICA stenosis.

Results

Compared to REACT, CE-MRA showed better delineation for the CCA and ICA (C1 and C2 segments) (median 5, range 2–5 vs. 4, range 3–5; P < 0.05). For the ICA (C1 and C2 segments), REACT provided a higher signal (5, range 3–5; P < 0.05/4.5, range 3–5; P > 0.05 vs. 4, range 2–5) and contrast (5, range 3–5 vs. 4, range 2–5; P > 0.05) than CE-MRA. The remaining segments of the blood-supplying vessels showed equal medians. There was no significant difference regarding artifacts, whereas REACT provided significantly lower image noise (4, range 3–5 vs. 4 range 2–5; P < 0.05) with a higher aSNR (P < 0.05) and aCNR (P < 0.05) for all vessels combined. For clinically relevant (≥50%) ICA stenosis, REACT achieved a detection sensitivity of 93.75% and a specificity of 100%.

Conclusion

Given its fast acquisition, comparable image quality to CE-MRA and high sensitivity and specificity for the detection of ICA stenosis, REACT was proven to be a clinically applicable method to assess extracranial arteries in AIS.

Electronic supplementary material

The online version of this article (10.1007/s00062-020-00963-6) contains supplementary material, which is available to authorized users.

High spatial resolution whole-neck MR angiography using thin-slab stack-of-stars quiescent interval slice-selective acquisition

PURPOSE

To report a 3D multi-echo thin-slab stack-of-stars (tsSOS) quiescent-interval slice-selective (QISS) strategy for high-resolution magnetic resonance angiography (MRA) of the entire neck in under seven minutes.

METHODS

The neck arteries of eight subjects were imaged at 3 Tesla. Multi-echo 3D tsSOS QISS using a FLASH readout was compared with 3D tsSOS FLASH, 2D QISS, 2D TOF, and 3D TOF. A root-mean-square (RMS) combination of echo time images was tested. Evaluation metrics included arterial signal-to-noise ratio (SNR), arterial-to-muscle contrast-to-noise ratio (CNR), and image quality.

RESULTS

3D multi-echo tsSOS QISS using a RMS combination of echo time images increased SNR and CNR by 60% and 63% with respect to the reconstruction obtained with the shortest echo time. 3D tsSOS QISS showed superior CNR with respect to 3D tsSOS FLASH imaging, and more than 3-fold higher SNR and CNR with respect to 2D radial QISS when normalized for voxel size. 3D tsSOS QISS provided good to excellent image quality that exceeded the image quality of 2D QISS, 2D TOF, and 3D TOF (P < .05).

CONCLUSION

Whole-neck high-resolution nonenhanced MRA is feasible using 3D tsSOS QISS, and produced image quality that exceeded those of competing nonenhanced MRA protocols at 3 Tesla.

Feasibility of a sub-3-minute imaging strategy for ungated quiescent interval slice-selective MRA of the extracranial carotid arteries using radial k-space sampling and deep learning-based image processing

PURPOSE

To develop and test the feasibility of a sub-3-minute imaging strategy for non-contrast evaluation of the extracranial carotid arteries using ungated quiescent interval slice-selective (QISS) MRA, combining single-shot radial sampling with deep neural network-based image processing to optimize image quality.

METHODS

The extracranial carotid arteries of 12 human subjects were imaged at 3 T using ungated QISS MRA. In 7 healthy volunteers, the effects of radial and Cartesian k-space sampling, single-shot and multishot image acquisition (1.1-3.3 seconds/slice, 141-423 seconds/volume), and deep learning-based image processing were evaluated using segmental image quality scoring, arterial temporal SNR, arterial-to-background contrast and apparent contrast-to-noise ratio, and structural similarity index. Comparison of deep learning-based image processing was made with block matching and 3D filtering denoising.

RESULTS

Compared with Cartesian sampling, radial k-space sampling increased arterial temporal SNR 107% (P < .001) and improved image quality during 1-shot imaging (P < .05). The carotid arteries were depicted with similar image quality on the rapid 1-shot and much lengthier 3-shot radial QISS protocols (P = not significant), which was corroborated in patient studies. Deep learning-based image processing outperformed block matching and 3D filtering denoising in terms of structural similarity index (P < .001). Compared with original QISS source images, deep learning image processing provided 24% and 195% increases in arterial-to-background contrast (P < .001) and apparent contrast-to-noise ratio (P < .001), and provided source images that were preferred by radiologists (P < .001).

CONCLUSION

Rapid, sub-3-minute evaluation of the extracranial carotid arteries is feasible with ungated single-shot radial QISS, and benefits from the use of deep learning-based image processing to enhance source image quality.

Non-Contrast-Enhanced Carotid MRA: Clinical Evaluation of a Novel Ungated Radial Quiescent-Interval Slice-Selective MRA at 1.5T

BACKGROUND AND PURPOSE

Non-contrast-enhanced MRA techniques have experienced a renaissance due to the known correlation between the use of gadolinium-based contrast agents and the development of nephrogenic systemic fibrosis and the deposition of gadolinium in some brain regions. The purpose of this study was to assess the diagnostic performance of ungated non-contrast-enhanced radial quiescent-interval slice-selective MRA of the extracranial supra-aortic arteries in comparison with conventional contrast-enhanced MRA in patients with clinical suspicion of carotid stenosis.

MATERIALS AND METHODS

In this prospective study, both MRA pulse sequences were performed in 31 consecutive patients (median age, 68.8 years; 19 men). For the evaluation, the cervical arterial system was divided into 35 segments (right and left side). Three blinded reviewers separately evaluated these segments. An ordinal scoring system was used to assess the image quality of arterial segments and the stenosis grading of carotid arteries.

RESULTS

Overall venous contamination in quiescent-interval slice-selective MRA was rated as "none" by all readers in 84.9% of cases and in 8.1% of cases in contrast-enhanced MRA (P < .0001). The visualization quality of arterial segments was considered good to excellent in 40.2% for the quiescent-interval slice-selective MRA and in 52.2% for the contrast-enhanced MRA (P < .0001). The diagnostic accuracy of ungated quiescent-interval slice-selective MRA concerning the stenosis grading showed a total sensitivity and specificity of 85.7% and 90.0%, respectively.

CONCLUSIONS

Ungated quiescent-interval slice-selective MRA can be used clinically as an alternative to contrast-enhanced MRA without a significantly different image quality or diagnostic accuracy for the detection of carotid stenosis at 1.5T.

In vivo accuracy of tooth surface reconstruction based on CBCT and dental MRI-A clinical pilot study

OBJECTIVES

Guided implant surgery (GIS) requires alignment of virtual models to reconstructions of three-dimensional imaging. Accurate visualization of the tooth surfaces in the imaging datasets is mandatory. In this prospective clinical study, in vivo tooth surface accuracy was determined for GIS using cone-beam computed tomography (CBCT) and dental magnetic resonance imaging (dMRI).

MATERIALS AND METHODS

CBCT and 3-Tesla dMRI were performed in 22 consecutive patients (mean age: 54.4 ± 15.2 years; mean number of restorations per jaw: 6.7 ± 2.7). Altogether, 92 teeth were included (31 incisor, 29 canines, 20 premolars, and 12 molars). Surfaces were reconstructed semi-automatically and registered to a reference standard (3D scans of stone models made from full-arch polyether impressions). Reliability of both methods was assessed using intraclass correlation coefficients. Accuracy was evaluated using the two one-sided tests procedure with a predefined equivalence margin of ±0.2 mm root mean square (RMS).

RESULTS

Inter- and intrarater reliability of tooth surface reconstruction were comparable for CBCT and dMRI. Geometric deviations were 0.102 ± 0.042 mm RMS for CBCT and 0.261 ± 0.08 mm RMS for dMRI. For a predefined equivalence margin, CBCT and dMRI were statistically equivalent. CBCT, however, was significantly more accurate (p ≤ .0001). For both imaging techniques, accuracy did not differ substantially between different tooth types.

CONCLUSION

Cone-beam computed tomography is an accurate and reliable imaging technique for tooth surfaces in vivo, even in the presence of metal artifacts. In comparison, dMRI in vivo accuracy is lower. Still, it allows for tooth surface reconstruction in satisfactory detail and within acceptable acquisition times.