Magnetic resonance imaging of the upper abdomen using a free-breathing T2-weighted turbo spin echo sequence with navigator triggered prospective acquisition correction

Usefulness of Breath-Hold Fat-Suppressed T2-Weighted Images With Deep Learning-Based Reconstruction of the Liver: Comparison to Conventional Free-Breathing Turbo Spin Echo

OBJECTIVES

The aim of this study was to evaluate the usefulness of breath-hold turbo spin echo with deep learning-based reconstruction (BH-DL-TSE) in acquiring fat-suppressed T2-weighted images (FS-T2WI) of the liver by comparing this method with conventional free-breathing turbo spin echo (FB-TSE) and breath-hold half Fourier single-shot turbo spin echo with deep learning-based reconstruction (BH-DL-HASTE).

MATERIALS AND METHODS

The study cohort comprised 111 patients with suspected liver disease who underwent 3 T magnetic resonance imaging. Fifty-eight focal solid liver lesions ≥10 mm were also evaluated. Three sets of FS-T2WI were acquired using FB-TSE, prototypical BH-DL-TSE, and prototypical BH-DL-HASTE, respectively. In the qualitative analysis, 2 radiologists evaluated the image quality using a 5-point scale. In the quantitative analysis, we calculated the lesion-to-liver signal intensity ratio (LEL-SIR). Friedman test and Dunn multiple comparison test were performed to assess differences among 3 types of FS-T2WI with respect to image quality and LEL-SIR.

RESULTS

The mean acquisition time was 4 minutes and 43 seconds ± 1 minute and 21 seconds (95% confidence interval, 4 minutes and 28 seconds to 4 minutes and 58 seconds) for FB-TSE, 40 seconds for BH-DL-TSE, and 20 seconds for BH-DL-HASTE. In the qualitative analysis, BH-DL-HASTE resulted in the fewest respiratory motion artifacts ( P < 0.0001). BH-DL-TSE and FB-TSE exhibited significantly less motion-related signal loss and clearer intrahepatic vessels than BH-DL-HASTE ( P < 0.0001). Regarding the edge sharpness of the left lobe, BH-DL-HASTE scored the highest ( P < 0.0001), and BH-DL-TSE scored higher than FB-TSE ( P = 0.0290). There were no significant differences among 3 types of FS-T2WI with respect to the edge sharpness of the right lobe ( P = 0.1290), lesion conspicuity ( P = 0.5292), and LEL-SIR ( P = 0.6026).

CONCLUSIONS

BH-DL-TSE provides a shorter acquisition time and comparable or better image quality than FB-TSE, and could replace FB-TSE in acquiring FS-T2WI of the liver. BH-DL-TSE and BH-DL-HASTE have their own advantages and may be used complementarily.

Clinical Impact of Deep Learning Reconstruction in MRI

Deep learning has been recognized as a paradigm-shifting tool in radiology. Deep learning reconstruction (DLR) has recently emerged as a technology used in the image reconstruction process of MRI, which is an essential procedure in generating MR images. Denoising, which is the first DLR application to be realized in commercial MRI scanners, improves signal-to-noise ratio. When applied to lower magnetic field-strength scanners, the signal-to-noise ratio can be increased without extending the imaging time, and image quality is comparable to that of higher-field-strength scanners. Shorter imaging times decrease patient discomfort and reduce MRI scanner running costs. The incorporation of DLR into accelerated acquisition imaging techniques, such as parallel imaging or compressed sensing, shortens the reconstruction time. DLR is based on supervised learning using convolutional layers and is divided into the following three categories: image domain, k-space learning, and direct mapping types. Various studies have reported other derivatives of DLR, and several have shown the feasibility of DLR in clinical practice. Although DLR efficiently reduces Gaussian noise from MR images, denoising makes image artifacts more prominent, and a solution to this problem is desired. Depending on the training of the convolutional neural network, DLR may change the imaging features of lesions and obscure small lesions. Therefore, radiologists may need to adopt the habit of questioning whether any information has been lost on images that appear clean. ^©RSNA, 2023 Quiz questions for this article are available in the supplemental material.

Accelerated T2-weighted MRI of the liver at 3 T using a single-shot technique with deep learning-based image reconstruction: impact on the image quality and lesion detection

PURPOSE

Fat-suppressed T2-weighted imaging (T2-FS) requires a long scan time and can be wrought with motion artifacts, urging the development of a shorter and more motion robust sequence. We compare the image quality of a single-shot T2-weighted MRI prototype with deep-learning-based image reconstruction (DL HASTE-FS) with a standard T2-FS sequence for 3 T liver MRI.

METHODS

41 consecutive patients with 3 T abdominal MRI examinations including standard T2-FS and DL HASTE-FS, between 5/6/2020 and 11/23/2020, comprised the study cohort. Three radiologists independently reviewed images using a 5-point Likert scale for artifact and image quality measures, while also assessing for liver lesions.

RESULTS

DL HASTE-FS acquisition time was 54.93 ± 16.69, significantly (p < .001) shorter than standard T2-FS (114.00 ± 32.98 s). DL HASTE-FS received significantly higher scores for sharpness of liver margin (4.3 vs 3.3; p < .001), hepatic vessel margin (4.2 vs 3.3; p < .001), pancreatic duct margin (4.0 vs 1.9; p < .001); in-plane (4.0 vs 3.2; p < .001) and through-plane (3.9 vs 3.4; p < .001) motion artifacts; other ghosting artifacts (4.3 vs 2.9; p < .001); and overall image quality (4.0 vs 2.9; p < .001), in addition to receiving a higher score for homogeneity of fat suppression (3.7 vs 3.4; p = .04) and liver-fat contrast (p = .03). For liver lesions, DL HASTE-FS received significantly higher scores for sharpness of lesion margin (4.4 vs 3.7; p = .03).

CONCLUSION

Novel single-shot T2-weighted MRI with deep-learning-based image reconstruction demonstrated superior image quality compared with the standard T2-FS sequence for 3 T liver MRI, while being acquired in less than half the time.

With 3 Types of Respiratory Acquisition: 3.0 T Respiratory Triggered Acquisition Can Obtain Higher Quality DWI Images of the Upper Abdomen

Objective

To compare the effects of 1.5 T and 3.0 T upper abdominal magnetic resonance diffusion-weighted imaging (DWI) under three acquisition techniques of breath holding, breath triggering, and free breathing, so as to provide a reference for the usage of upper abdominal DWI scanning.

Methods

Twenty-one healthy subjects were selected from social volunteers and underwent routine magnetic resonance imaging (MRI) and DWI on 1.5 T and 3.0 T, respectively. DWI included three acquisition methods: breath triggering, breath holding, and free breathing, and b values were 100 and 800. The DWI image artifacts, image quality, apparent diffusion coefficient (ADC), and the signal-to-noise ratio (SNR) obtained through the three acquisition methods were compared.

Results

The 1.5 T free-breathing DWI image quality was the best, while the 3.0 T had the best breath-triggered DWI image quality. The 3.0 T breath-triggered DWI image quality was better than the 1.5 T free-breathing DWI image (P=0.012), and the SNR of free-breathing DWI was the highest. Between the two field intensities, the SNR of the liver in the 3.0 T group was much lower than that in the 1.5 T group, and obvious differences were not observed in ADC values of normal liver, gallbladder, kidney, spleen, and pancreas.

Conclusion

3.0 T respiratory-triggered acquisition can obtain higher quality DWI images. But in the case of only 1.5 T field strength, free-breathing acquisition of DWI images should be selected.

Fast T2-weighted liver MRI: Image quality and solid focal lesions conspicuity using a deep learning accelerated single breath-hold HASTE fat-suppressed sequence

PURPOSE

Acceleration of MRI acquisitions and especially of T2-weighted sequences is essential to reduce the duration of MRI examinations but also kinetic artifacts in liver imaging. The purpose of this study was to compare the acquisition time and the image quality of a single-shot fat-suppressed turbo spin-echo (TSE) T2-weighted sequence with deep learning reconstruction (HASTE_DL) with that of a fat-suppressed T2-weighted BLADE TSE sequence in patients with focal liver lesions.

MATERIALS AND METHODS

Ninety-five patients (52 men, 43 women; mean age: 61 ± 14 [SD]; age range: 28-87 years) with 42 focal liver lesions (17 hepatocellular carcinomas, 10 sarcoidosis lesions, 9 myeloma lesions, 3 liver metastases and 3 focal nodular hyperplasias) who underwent liver MRI at 1.5 T including HASTE_DL and BLADE sequences were retrospectively included. Overall image quality, noise level in the liver, lesion conspicuity and sharpness of liver lesion contours were assessed by two independent readers. Liver signal-to-noise ratio (SNR) and lesion contrast-to-noise ratio (CNR) were measured and compared between the two sequences, as well as the mean duration of the sequences (Student t-test or Wilcoxon test for paired data).

RESULTS

Median overall quality on HASTE_DL images (3; IQR: 3, 3) was significantly greater than that on BLADE images (2; IQR: 1, 3) (P < 0.001). Median noise level in the liver on HASTE_DL images (0; IQR: 0, 0.5) was significantly lower than that on BLADE images (1; IQR: 1, 2) (P < 0.001). On HASTE_DL images, mean liver SNR (107.3 ± 39.7 [SD]) and mean focal liver lesion CNR (87.0 ± 76.6 [SD]) were significantly greater than those on BLADE images (67.1 ± 23.8 [SD], P < 0.001 and 48.6 ± 43.9 [SD], P = 0.027, respectively). Acquisition time was significantly shorter with the HASTE_DL sequence (18 ± [0] s; range: 18-18 s) compared to BLADE sequence (152 ± 47 [SD] s; range: 87-263 s) (P < 0.001).

CONCLUSION

By comparison with the BLADE sequence, HASTE_DL sequence significantly reduces acquisition time while improving image quality, liver SNR and focal liver lesions CNR.

Single-Breath-Hold MRI-SPACE Cholangiopancreatography with Compressed Sensing versus Conventional Respiratory-Triggered MRI-SPACE Cholangiopancreatography at 3Tesla: Comparison of Image Quality and Diagnostic Confidence

To compare two magnetic resonance cholangiopancreatography (MRCP) sequences at 3 Tesla (3T): the conventional 3D Respiratory-Triggered SPACE sequence (RT-MRCP) and a prototype 3D Compressed-Sensing Breath-Hold SPACE sequence (CS-BH-MRCP), in terms of qualitative and quantitative image quality and radiologist's diagnostic confidence for detecting common bile duct (CBD) lithiasis, biliary anastomosis stenosis in liver-transplant recipients, and communication of pancreatic cyst with the main pancreatic duct (MPD). Sixty-eight patients with suspicion of choledocholithiasis or biliary anastomosis stenosis after liver transplant, or branch-duct intraductal papillary mucinous neoplasm of the pancreas (BD-IPMN), were included. The relative CBD to peri-biliary tissues (PBT) contrast ratio (CR) was assessed. Overall image quality, presence of artefacts, background noise suppression and the visualization of 12 separated segments of the pancreatic and bile ducts were evaluated by two observers working independently on a five-point scale. Diagnostic confidence was scored on a 1-3 scale. The CS-BH-MRCP presented significantly better CRs (p < 0.0001), image quality (p = 0.004), background noise suppression (p = 0.011), fewer artefacts (p = 0.004) and better visualization of pancreatic and bile ducts segments with the exception of the proximal CBD (p = 0.054), cystic duct confluence (p = 0.459), the four secondary intrahepatic bile ducts, and central part of the MPD (p = 0.885) for which no significant differences were found. Overall, diagnostic confidence was significantly better with the CS-BH-MRCP sequence for both readers (p = 0.038 and p = 0.038, respectively). This study shows that the CS-BH-MRCP sequence presents overall better image quality and bile and pancreatic ducts visualization compared to the conventional RT-MRCP sequence at 3T.

Three-Dimensional (3D) Breath-Hold Zoomed MR Cholangiopancreatography (MRCP): Evaluation of Additive Value to Conventional 3D Navigator Triggering MRCP in Patients With Branch Duct Intraductal Papillary Mucinous Neoplasms

BACKGROUND

To resolve drawbacks of navigator triggering (NT) three-dimensional (3D) magnetic resonance cholangiopancreatography (MRCP), several approaches were proposed to obtain 3D MRCP within a single breath-hold (BH). However, reduced field-of-view technique in the phase-encoding direction combined with two-dimensional spatially selective radiofrequency excitation pulses has not yet been applied to 3D BH MRCP.

PURPOSE

To investigate the feasibility and the complementary value of 3D BH zoomed MRCP to conventional 3D NT MRCP in patients with branch duct intraductal papillary mucinous neoplasms (BD-IPMNs) of the pancreas.

STUDY TYPE

Retrospective.

POPULATION

A total of 221 patients (116 male and 105 female, median age 73 years) with BD-IPMNs.

FIELD STRENGTH/SEQUENCE

3.0 T/3D turbo spin echo ASSESSMENT: MR images were analyzed by three radiologists (R.M., H.O., M.T., with 1, 13, and 17 years of experience) to compare blurring and motion artifacts, background suppression, visualization of main pancreatic duct (MPD), conspicuity of BD-IPMN, and overall image quality.

STATISTICAL TESTS

Wilcoxon-signed rank, Mann-Whitney U, chi-squared or Fisher's exact tests (P < 0.05).

RESULTS

Image quality was significantly higher on 3D NT MRCP images than on 3D BH zoomed MRCP (median (interquartile range); background suppression, 4 (4-4) vs. 3 (3-4); visualization of MPD, 4 (3-4) vs. 4 (3-4), conspicuity of BD-IPMN, 4 (3-4) vs. 3 (3-4); and overall image quality, 3 (3-4) vs. 3 (3-3)). However, in 32 (14%) patients, 3D NT MRCP showed a score of 1 or 2 in overall image quality. Regarding the conspicuity of BD-IPMN, a conspicuity score of 1 or 2 was rendered in 31 (14%) patients in 3D NT MRCP group. Conversely, 3D BH zoomed MRCP showed a score of 3 or 4 in 29 (94%) of these 31 patients.

DATA CONCLUSION

3D BH zoomed MRCP plays a complementary role to 3D NT MRCP, and may improve the conspicuity of BD-IPMNs in patients with irregular breathing pattern.

LEVEL OF EVIDENCE

4 TECHNICAL EFFICACY: Stage 2.

Accelerated single-shot T2-weighted fat-suppressed (FS) MRI of the liver with deep learning-based image reconstruction: qualitative and quantitative comparison of image quality with conventional T2-weighted FS sequence

OBJECTIVE

To compare the image quality of an accelerated single-shot T2-weighted fat-suppressed (FS) MRI of the liver with deep learning-based image reconstruction (DL HASTE-FS) with conventional T2-weighted FS sequence (conventional T2 FS) at 1.5 T.

METHODS

One hundred consecutive patients who underwent clinical MRI of the liver at 1.5 T including the conventional T2-weighted fat-suppressed sequence (T2 FS) and accelerated single-shot T2-weighted MRI of the liver with deep learning-based image reconstruction (DL HASTE-FS) were included. Images were reviewed independently by three blinded observers who used a 5-point confidence scale for multiple measures regarding the artifacts and image quality. Descriptive statistics and McNemar's test were used to compare image quality scores and percentage of lesions detected by each sequence, respectively. Intra-class correlation coefficient (ICC) was used to assess consistency in reader scores.

RESULTS

Acquisition time for DL HASTE-FS was 51.23 +/ 10.1 s, significantly (p < 0.001) shorter than conventional T2-FS (178.9 ± 85.3 s). DL HASTE-FS received significantly higher scores than conventional T2-FS for strength and homogeneity of fat suppression; sharpness of liver margin; sharpness of intra-hepatic vessel margin; in-plane and through-plane respiratory motion; other ghosting artefacts; liver-fat contrast; and overall image quality (all, p < 0.0001). DL HASTE-FS also received higher scores for lesion conspicuity and sharpness of lesion margin (all, p < .001), without significant difference for liver lesion contrast (p > 0.05).

CONCLUSIONS

Accelerated single-shot T2-weighted MRI of the liver with deep learning-based image reconstruction showed superior image quality compared to the conventional T2-weighted fat-suppressed sequence despite a 4-fold reduction in acquisition time.

KEY POINTS

• Conventional fat-suppressed T2-weighted sequence (conventional T2 FS) can take unacceptably long to acquire and is the most commonly repeated sequence in liver MRI due to motion. • DL HASTE-FS demonstrated superior image quality, improved respiratory motion and other ghosting artefacts, and increased lesion conspicuity with comparable liver-to-lesion contrast compared to conventional T2FS sequence. • DL HASTE- FS has the potential to replace conventional T2 FS sequence in routine clinical MRI of the liver, reducing the scan time, and improving the image quality.

Monitoring and Synchronization of Cardiac and Respiratory Traces in Magnetic Resonance Imaging: A Review

Synchronization of human vital signs, namely the cardiac cycle and respiratory excursions, is necessary during magnetic resonance imaging of the cardiovascular system and the abdominal cavity to achieve optimal image quality with minimized artifacts. This review summarizes techniques currently available in clinical practice, as well as methods under development, outlines the benefits and disadvantages of each approach, and offers some unique solutions for consideration.

Navigator-triggered and breath-hold 3D MRCP using compressed sensing: image quality and method selection factor assessment

PURPOSE

To examine whether MRCP using a combination of compressed sensing and sensitivity encoding with navigator-triggered and breath-hold techniques (NT C-SENSE and BH C-SENSE, respectively) have comparable image quality to that of navigator-triggered MRCP using only sensitivity encoding (NT SENSE) at 1.5-T.

METHODS

Fifty-one participants were enrolled in this prospective study between July and October 2018 and underwent the three 3D MRCP sequences each. The acquisition time and relative duct-to-periductal contrast ratios (RC values) of each bile duct segment were obtained. Visualization of the bile and main pancreatic ducts, background suppression, artifacts, and overall image quality were scored on 5-point scales. Mean and median differences in RC values and qualitative scores of NT C-SENSE and BH C-SENSE relative to NT SENSE were calculated with 95% confidence intervals (CIs).

RESULTS

Acquisition time of NT SENSE, NT C-SENSE, and BH C-SENSE were 348, 143 (mean for both), and 18 s (for all participants), respectively. The RC value of each bile duct segment was inferior, but the lower limits of the 95% CIs of the mean differences were ≥ - 0.10, for both NT C-SENSE and BH C-SENSE. The visualization score of the intrahepatic duct in BH C-SENSE was inferior to that in NT SENSE (lower 95% CI limit, - 1.5). In both NT C-SENSE and BH C-SENSE, the 95% CIs of the median differences in the other qualitative scores were from - 1.0 to 0.0.

CONCLUSION

NT C-SENSE and BH C-SENSE have comparable image quality to NT SENSE at 1.5-T.

Improved Liver Diffusion-Weighted Imaging at 3 T Using Respiratory Triggering in Combination With Simultaneous Multislice Acceleration

OBJECTIVES

The aim of this study was to retrospectively compare optimized respiratory-triggered diffusion-weighted imaging with simultaneous multislice acceleration (SMS-RT-DWI) of the liver with a standard free-breathing echo-planar DWI (s-DWI) protocol at 3 T with respect to the imaging artifacts inherent to DWI.

MATERIALS AND METHODS

Fifty-two patients who underwent a magnetic resonance imaging study of the liver were included in this retrospective study. Examinations were performed on a 3 T whole-body magnetic resonance system (MAGNETOM Skyra; Siemens Healthcare, Erlangen, Germany). In all patients, both s-DWI and SMS-RT-DWI of the liver were obtained. Images were qualitatively evaluated by 2 independent radiologists with regard to overall image quality, liver edge sharpness, sequence-related artifacts, and overall scan preference. For quantitative evaluation, signal-to-noise ratio was measured from signal-to-noise ratio maps. The mean apparent diffusion coefficient (ADC) was measured in each liver quadrant. The Wilcoxon rank-sum test was used for analysis of the qualitative parameters and the paired Student t test for quantitative parameters.

RESULTS

Overall image quality, liver edge sharpness, and sequence-related artifacts of SMS-RT-DWI received significantly better ratings compared with s-DWI (P < 0.05 for all). For 90.4% of the examinations, both readers overall preferred SMS-RT-DWI to s-DWI. Acquisition time for SMS-RT-DWI was 34% faster than s-DWI. Signal-to-noise ratio values were significantly higher for s-DWI at b50 but did not statistically differ at b800, and they were more homogenous for SMS-RT-DWI, with a significantly lower standard deviation at b50. Mean ADC values decreased from the left to right hepatic lobe as well as from cranial to caudal for s-DWI. With SMS-RT-DWI, mean ADC values were homogeneous throughout the liver.

CONCLUSIONS

Optimized, multislice, respiratory-triggered DWI of the liver at 3 T substantially improves image quality with a reduced scan acquisition time compared with s-DWI.

Quantification of MRI T2-weighted High Signal Volume in Cystic Fibrosis: A Pilot Study

Background In patients with cystic fibrosis (CF), pulmonary structures with high MRI T2 signal intensity relate to inflammatory changes in the lung and bronchi. These areas of pathologic abnormalities can serve as imaging biomarkers. The feasibility of automated quantification is unknown. Purpose To quantify the MRI T2 high-signal-intensity lung volume and T2-weighted volume-intensity product (VIP) by using a black-blood T2-weighted radial fast spin-echo sequence in participants with CF. Materials and Methods Healthy individuals and study participants with CF were prospectively enrolled between January 2017 and November 2017. All participants underwent a lung MRI protocol including T2-weighted radial fast spin-echo sequence. Participants with CF also underwent pulmonary function tests the same day. Participants with CF exacerbation underwent repeat MRI after their treatment with antibiotics. Two observers supervised automated quantification of T2-weighted high-signal-intensity volume (HSV) and T2-weighted VIP independently, and the average score was chosen as consensus. Statistical analysis used the Mann-Whitney test for comparison of medians, correlations used the Spearman test, comparison of paired medians used the Wilcoxon signed rank test, and reproducibility was evaluated by using intraclass correlation coefficient. Results In 10 healthy study participants (median age, 21 years [age range, 18-27 years]; six men) and 12 participants with CF (median age, 18 years [age range, 9-40 years]; eight men), T2-weighted HSV was equal to 0% and 4.1% (range, 0.1%-17%), respectively, and T2-weighted VIP was equal to 0 msec and 303 msec (range, 39-1012 msec), respectively (P < .001). In participants with CF, T2-weighted HSV or T2-weighted VIP were associated with forced expiratory volume in 1 second percentage predicted (ρ = -0.88 and ρ = -0.94, respectively; P < .001). In six participants with CF exacerbation and follow-up after treatment, a decrease in both T2-weighted HSV and T2-weighted VIP was observed (P = .03). The intra- and interobserver reproducibility of MRI were good (intraclass correlation coefficients, >0.99 and >0.99, respectively). Conclusion In patients with cystic fibrosis (CF), automated quantification of lung MRI high-signal-intensity volume was reproducible and correlated with pulmonary function testing severity, and it improved after treatment for CF exacerbation. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Revel and Chassagnon in this issue.

Clinical Evaluation of Respiratory-triggered 3D MRCP with Navigator Echoes Compared to Breath-hold Acquisition Using Compressed Sensing and/or Parallel Imaging

Purpose:

To compare the image quality of three-dimensional magnetic resonance cholangiopancreatography (MRCP) acquired with respiratory triggering against breath-hold 3D MRCP with compressed sensing (CS) and parallel imaging (PI) in a clinical setting.

Methods:

This study included 93 patients (45 men, mean age: 69.7 ± 9.3 years), in whom three types of 3D MRCP were performed: 3D breath-hold MRCP with CS and PI reconstruction (BH-CS-MRCP) and PI only reconstruction (BH-PI-MRCP) additionally to 3D respiratory triggered MRCP with navigator echoes (Nav-MRCP). Duct visualization and overall image quality were blindly evaluated on a four-point scale by two independent radiologists. Quantitative analysis was performed by calculating the relative duct-to-periductal contrast (RC) of three main biliary segments. Comparison between the methods was performed using paired t-test.

Results:

Acquisition time was 23 s for both breath-hold MRCP protocols and 1 min 29 s for Nav-MRCP. Mean grading (Nav/CS/PI) for common bile duct (2.74/2.87/2.94), common hepatic duct (2.82/2.92/3.00), central right hepatic duct (2.75/2.85/2.98), central left hepatic duct (2.75/2.85/2.92) and cystic duct (2.22/2.34/2.42) was higher in BH-CS- and BH-PI-MRCP, whereas Nav-MRCP showed higher grading in the peripheral segments (peripheral right hepatic duct: 2.24/2.01/2.12; peripheral left hepatic duct: 2.23/2.02/2.13). Overall image quality of Nav-MRCP (2.91 ± 0.7) was not different from BH-PI-MRCP (2.92 ± 0.6) (P = 0.163), but higher than BH-CS-MRCP (2.80 ± 0.7) (P = 0.031). Quantitative analysis showed lower RC values for CS- and PI-MRCP than Nav-MRCP (P < 0.001).

Conclusion:

Breath-hold 3D MRCP were feasible using PI and CS. Visualization of the greater ductal system was even superior in breath-hold MRCP than in Nav-MRCP by considerably reducing acquisition time. Both breath-hold methods are suitable for revised MRI protocols notably in patients with irregular respiratory cycle.

Evaluation of a free-breathing respiratory-triggered (Navigator) 3-D T1-weighted (T1W) gradient recalled echo sequence (LAVA) for detection of enhancement in cystic and solid renal masses

OBJECTIVES

To evaluate free-breathing Navigator-triggered 3-D T1-weighted MRI (NAV-LAVA) compared to breath-hold (BH)-LAVA among cystic and solid renal masses.

MATERIALS AND METHODS

With an IRB waiver, 44 patients with 105 renal masses (71 non-enhancing cysts and 14 cystic and 20 solid renal masses) underwent MRI between 2016 and 2017 where BH-LAVA and NAV-LAVA were performed. Subtraction images were generated for BH-LAVA and NAV-LAVA using pre- and 3-min post-gadolinium-enhanced images and were evaluated by two blinded radiologists for overall image quality, image sharpness, motion artifact, and quality of subtraction (using 5-point Likert scales) and presence/absence of enhancement. Percentage signal intensity change (Δ%SI) = ([SI.post-gadolinium-SI.pre-gadolinium]/SI.pre-gadolinium)*100, was measured on BH-LAVA and NAV-LAVA. Likert scores were compared using Wilcoxon's sign-rank test and accuracy for detection of enhancement compared using receiver operator characteristic (ROC) analysis.

RESULTS

Overall image quality (p = 0.002-0.141), image sharpness (p = 0.002-0.031), and motion artifact were better (p = 0.002) comparing BH-LAVA to NAV-LAVA for both radiologists; however, quality of image subtraction did not differ between groups (p = 0.09-0.14). Sensitivity/specificity/area under ROC curve for enhancement in cystic and solid renal masses using subtraction and %SIΔ were (1) BH-LAVA: 64.7%/98.6%/0.82 (radiologist 1), 61.8%/95.8%/0.79 (radiologist 2), and 70.6%/81.7%/0.76 (%SIΔ) versus 2) NAV-LAVA: 58.8%/95.8%/0.79 (radiologist 1, p = 0.16), 58.8%/88.7%/0.73 (radiologist 2, p = 0.37), and 73.5%/76.1%/0.75 (%SIΔ, p = 0.74).

CONCLUSIONS

NAV-LAVA showed similar quality of subtraction and ability to detect enhancement compared to BH-LAVA in renal masses albeit with lower image quality, image sharpness, and increased motion artifact. NAV-LAVA may be considered in renal MRI for patients where BH is suboptimal.

KEY POINTS

• Free-breathing Navigator (NAV) 3-D subtraction MRI is comparable to breath-hold (BH) images. • Accuracy for subjective and quantitative diagnosis of enhancement in renal masses on NAV 3-D T1W is comparable to BH MRI. • NAV 3-D T1W renal MRI is useful in patients who may not be able to adequately BH.

Free-breathing abdominal MRI improved by repeated k-t-subsampling and artifact-minimization (ReKAM)

PURPOSE

We report an approach, termed Repeated k-t-subsampling and artifact-minimization (ReKAM), for removing motion artifacts in free-breathing abdominal MRI. The method is particularly valuable for challenging patients who may not hold their breath for a long time or have irregular respiratory rate.

METHODS

The ReKAM framework comprises one acquisition module and two reconstruction modules. A fast MRI sequence is used to repeatedly acquire multiple sets of k-t space data. Motion artifacts are then minimized by two reconstruction modules: (a) a bootstrapping module in k-t-space is used to identify a low-artifact image; (b) a constrained reconstruction module that integrates projection onto convex set (POCS) and multiplexed sensitivity encoding (MUSE), termed POCSMUSE, is applied to further remove residual artifact. The ReKAM framework is compatible with different pulse sequences, and generally applicable to irregular data sampling patterns in k-space. Free-breathing fast spin-echo MRI data, acquired from healthy volunteers and patients, were used to evaluate the developed ReKAM method.

RESULTS

Experimental results show that the ReKAM technique can produce high-quality free-breathing images with the artifact levels comparable to that of breath-holding MRI.

CONCLUSION

The ReKAM framework improves the quality of free-breathing abdominal MRI data, and is compatible with various MRI pulse sequences.

Silent navigator-triggered silent MRI of the abdomen

PURPOSE

To develop and demonstrate the feasibility of a silent respiratory navigator technique for prospective triggering, which was incorporated into a three-dimensional radial zero-echo-time sequence for respiratory navigated silent abdominal imaging.

METHODS

A nonselective hard excitation radiofrequency pulse was used for the navigator sequence with a derated readout gradient, to avoid generation of high levels of acoustic noise. The acquired navigator signals were processed in real time and used for prospective triggering of the zero-echo-time sequence. Ten healthy volunteers were scanned using the proposed and conventional techniques at 1.5 T. An acoustic noise measurement with A-weighted continuous equivalent sound pressure level was also performed.

RESULTS

The sound pressure-level values of the background noise, zero-echo-time imaging, conventional, and silent navigators were 68.3, 68.4, 102.5, and 69.4 dBA, respectively. Excellent correlation with correlation coefficients greater than 0.9 was observed between the bellows signals and displacement values calculated from the navigators. Sharpness of the portal vein of both conventional and silent navigator-triggered images was significantly higher than those of nontriggered images.

CONCLUSIONS

The silent navigator-triggered zero-echo-time technique is feasible and might improve image quality and workflow of abdominal MRI of patients who are prone to acoustic noise. Magn Reson Med 79:2170-2175, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Supine Breast MRI Using Respiratory Triggering

RATIONALE AND OBJECTIVES

This study aims to evaluate if navigator-echo respiratory-triggered magnetic resonance acquisition can acquire supine high-quality breast magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Supine respiratory-triggered magnetic resonance imaging (Trig-MRI) was compared to supine non-Trig-MRI to evaluate breathing-induced motion artifacts (group 1), and to conventional prone non-Trig-MRI (group 2, 16-channel breast coil), all at 3T. A 32-channel thorax coil was placed on top of a cover to prevent breast deformation. Ten volunteers were scanned in each group, including one patient. The acquisition time was recorded. Image quality was compared by visual examination and by calculation of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and image sharpness (IS).

RESULTS

Scan time increased from 56.5 seconds (non-Trig-MRI) to an average of 306 seconds with supine Trig-MRI (range: 120-540 seconds). In group 1, the median values (interquartile range) of SNR, CNR, and IS improved from 11.5 (6.0), 7.3 (3.1), and 0.23 (0.2) cm on supine non-Trig-MRI to 38.1 (29.1), 32.8 (29.7), and 0.12 (0) cm (all P < 0.01) on supine Trig-MRI. All qualitative image parameters in group 1 improved on supine Trig-MRI (all P < 0.01). In group 2, SNR and CNR improved from 14.7 (6.8) and 12.6 (5.6) on prone non-Trig-MRI to 36.2 (12.2) and 32.7 (12.1) (both P < 0.01) on supine Trig-MRI. IS was similar: 0.10 (0) cm vs 0.11 (0) cm (P = 0.88).

CONCLUSIONS

Acquisition of high-quality supine breast MRI is possible when respiratory triggering is applied, in a similar setup as during subsequent treatment. Image quality improved when compared to supine non-triggered breast MRI and prone breast MRI, but at the cost of increased acquisition time.

Respiratory motion prediction and prospective correction for free-breathing arterial spin-labeled perfusion MRI of the kidneys

PURPOSE

Respiratory motion prediction using an artificial neural network (ANN) was integrated with pseudocontinuous arterial spin labeling (pCASL) MRI to allow free-breathing perfusion measurements in the kidney. In this study, we evaluated the performance of the ANN to accurately predict the location of the kidneys during image acquisition.

METHODS

A pencil-beam navigator was integrated with a pCASL sequence to measure lung/diaphragm motion during ANN training and the pCASL transit delay. The ANN algorithm ran concurrently in the background to predict organ location during the 0.7-s 15-slice acquisition based on the navigator data. The predictions were supplied to the pulse sequence to prospectively adjust the axial slice acquisition to match the predicted organ location. Additional navigators were acquired immediately after the multislice acquisition to assess the performance and accuracy of the ANN. The technique was tested in eight healthy volunteers.

RESULTS

The root-mean-square error (RMSE) and mean absolute error (MAE) for the eight volunteers were 1.91 ± 0.17 mm and 1.43 ± 0.17 mm, respectively, for the ANN. The RMSE increased with transit delay. The MAE typically increased from the first to last prediction in the image acquisition. The overshoot was 23.58% ± 3.05% using the target prediction accuracy of ± 1 mm.

CONCLUSION

Respiratory motion prediction with prospective motion correction was successfully demonstrated for free-breathing perfusion MRI of the kidney. The method serves as an alternative to multiple breathholds and requires minimal effort from the patient.

Strategies to minimize sedation in pediatric body magnetic resonance imaging

The high soft-tissue contrast of MRI and the absence of ionizing radiation make it a valuable tool for assessment of body pathology in children. Infants and young children are often unable to cooperate with awake MRI so sedation or general anesthesia might be required. However, given recent data on the costs and potential risks of anesthesia in young children, there is a need to try to decrease or avoid sedation in this population when possible. Child life specialists in radiology frequently use behavioral techniques and audiovisual support devices, and they practice with children and families using mock scanners to improve child compliance with MRI. Optimization of the MR scanner environment is also important to create a child-friendly space. If the child can remain inside the MRI scanner, a variety of emerging techniques can reduce the effect of involuntary motion. Using sequences with short acquisition times such as single-shot fast spin echo and volumetric gradient echo can decrease artifacts and improve image quality. Breath-holding, respiratory triggering and signal averaging all reduce respiratory motion. Emerging techniques such as radial and multislice k-space acquisition, navigator motion correction, as well as parallel imaging and compressed sensing reconstruction methods can further accelerate acquisition and decrease motion. Collaboration among radiologists, anesthesiologists, technologists, child life specialists and families is crucial for successful performance of MRI in young children.

T2-Weighted Liver MRI Using the MultiVane Technique at 3T: Comparison with Conventional T2-Weighted MRI

Objective

To assess the value of applying MultiVane to liver T2-weighted imaging (T2WI) compared with conventional T2WIs with emphasis on detection of focal liver lesions.

Materials and Methods

Seventy-eight patients (43 men and 35 women) with 86 hepatic lesions and 20 pancreatico-biliary diseases underwent MRI including T2WIs acquired using breath-hold (BH), respiratory-triggered (RT), and MultiVane technique at 3T. Two reviewers evaluated each T2WI with respect to artefacts, organ sharpness, and conspicuity of intrahepatic vessels, hilar duct, and main lesion using five-point scales, and made pairwise comparisons between T2WI sequences for these categories. Diagnostic accuracy (Az) and sensitivity for hepatic lesion detection were evaluated using alternative free-response receiver operating characteristic analysis.

Results

MultiVane T2WI was significantly better than BH-T2WI or RT-T2WI for organ sharpness and conspicuity of intrahepatic vessels and main lesion in both separate reviews and pairwise comparisons (p < 0.001). With regard to motion artefacts, MultiVane T2WI or BH-T2WI was better than RT-T2WI (p < 0.001). Conspicuity of hilar duct was better with BH-T2WI than with MultiVane T2WI (p = 0.030) or RT-T2WI (p < 0.001). For detection of 86 hepatic lesions, sensitivity (mean, 97.7%) of MultiVane T2WI was significantly higher than that of BH-T2WI (mean, 89.5%) (p = 0.008) or RT-T2WI (mean, 84.9%) (p = 0.001).

Conclusion

Applying the MultiVane technique to T2WI of the liver is a promising approach to improving image quality that results in increased detection of focal liver lesions compared with conventional T2WI.

Advances in functional and structural imaging of the human lung using proton MRI

The field of proton lung MRI is advancing on a variety of fronts. In the realm of functional imaging, it is now possible to use arterial spin labeling (ASL) and oxygen-enhanced imaging techniques to quantify regional perfusion and ventilation, respectively, in standard units of measurement. By combining these techniques into a single scan, it is also possible to quantify the local ventilation-perfusion ratio, which is the most important determinant of gas-exchange efficiency in the lung. To demonstrate potential for accurate and meaningful measurements of lung function, this technique was used to study gravitational gradients of ventilation, perfusion, and ventilation-perfusion ratio in healthy subjects, yielding quantitative results consistent with expected regional variations. Such techniques can also be applied in the time domain, providing new tools for studying temporal dynamics of lung function. Temporal ASL measurements showed increased spatial-temporal heterogeneity of pulmonary blood flow in healthy subjects exposed to hypoxia, suggesting sensitivity to active control mechanisms such as hypoxic pulmonary vasoconstriction, and illustrating that to fully examine the factors that govern lung function it is necessary to consider temporal as well as spatial variability. Further development to increase spatial coverage and improve robustness would enhance the clinical applicability of these new functional imaging tools. In the realm of structural imaging, pulse sequence techniques such as ultrashort echo-time radial k-space acquisition, ultrafast steady-state free precession, and imaging-based diaphragm triggering can be combined to overcome the significant challenges associated with proton MRI in the lung, enabling high-quality three-dimensional imaging of the whole lung in a clinically reasonable scan time. Images of healthy and cystic fibrosis subjects using these techniques demonstrate substantial promise for non-contrast pulmonary angiography and detailed depiction of airway disease. Although there is opportunity for further optimization, such approaches to structural lung imaging are ready for clinical testing.

Fetal MRI: A Technical Update with Educational Aspirations

Fetal magnetic resonance imaging (MRI) examinations have become well-established procedures at many institutions and can serve as useful adjuncts to ultrasound (US) exams when diagnostic doubts remain after US. Due to fetal motion, however, fetal MRI exams are challenging and require the MR scanner to be used in a somewhat different mode than that employed for more routine clinical studies. Herein we review the techniques most commonly used, and those that are available, for fetal MRI with an emphasis on the physics of the techniques and how to deploy them to improve success rates for fetal MRI exams. By far the most common technique employed is single-shot T2-weighted imaging due to its excellent tissue contrast and relative immunity to fetal motion. Despite the significant challenges involved, however, many of the other techniques commonly employed in conventional neuro- and body MRI such as T1 and T2*-weighted imaging, diffusion and perfusion weighted imaging, as well as spectroscopic methods remain of interest for fetal MR applications. An effort to understand the strengths and limitations of these basic methods within the context of fetal MRI is made in order to optimize their use and facilitate implementation of technical improvements for the further development of fetal MR imaging, both in acquisition and post-processing strategies.

Radial MRI during free breathing in contrast-enhanced hepatobiliary phase imaging

BACKGROUND

Use of gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) for diagnosis of hepatic tumors has been previously reported. Fat-saturated 3D T1-weighted gradient echo sequence (TIGRE) imaging using a breath-hold technique is usually used for dynamic studies and hepatobiliary phase Gd-EOB-DTPA-enhanced magnetic resonance imaging (MRI). In cases where the patient has difficulty holding their breath, this scanning method can be difficult.

PURPOSE

To investigate the usefulness of a fat-saturated T1-weighted spin-echo (SE) sequence using a radial read-out (radial acquisition regime-SE, RADAR-SE) during free breathing for hepatobiliary phase Gd-EOB-DTPA-enhanced MRI.

MATERIAL AND METHODS

Images were acquired at 1.5 T. First, a phantom with diluted Gd-EOB-DTPA was scanned using the TIGRE sequence and the RADAR-SE sequence. Contrast ratios of the sequences were compared. Next, the hepatobiliary phase was imaged in 62 patients using the TIGRE sequence with breath-hold and the RADAR-SE during free breathing. Qualitative and quantitative evaluations were compared.

RESULTS

In the phantom study, RADAR-SE had a higher contrast ratio than TIGRE. In the clinical study, artifacts were more conspicuous in RADAR-SE compared to TIGRE images in the qualitative evaluation. However, RADAR-SE images were equal to or better than TIGRE images in patients who had difficulty holding their breath. The signal intensity ratio of the liver was statistically higher using RADAR-SE than TIGRE.

CONCLUSION

RADAR-SE can be useful for hepatobiliary phase Gd-EOB-DTPA-enhanced MRI in patients who have difficulty holding their breath.

Pediatric hepatobiliary magnetic resonance imaging

Magnetic resonance (MR) imaging is an effective and noninvasive modality for evaluating hepatobiliary pathologic conditions. This article provides an up-to-date review of anatomy, indications, and imaging goals and protocols, including patient preparation, pulse sequences, and contrast agents used in pediatric MR hepatobiliary imaging. This article also highlights some of the common MR features of pediatric liver pathologic conditions, including tumors, congenital biliary ductal plate malformations, trauma, fibrosis, and infection.

A historical overview of magnetic resonance imaging, focusing on technological innovations

Magnetic resonance imaging (MRI) has now been used clinically for more than 30 years. Today, MRI serves as the primary diagnostic modality for many clinical problems. In this article, historical developments in the field of MRI will be discussed with a focus on technological innovations. Topics include the initial discoveries in nuclear magnetic resonance that allowed for the advent of MRI as well as the development of whole-body, high field strength, and open MRI systems. Dedicated imaging coils, basic pulse sequences, contrast-enhanced, and functional imaging techniques will also be discussed in a historical context. This article describes important technological innovations in the field of MRI, together with their clinical applicability today, providing critical insights into future developments.

Diffusion-weighted MRI in the assessment of split renal function: comparison of navigator-triggered prospective acquisition correction and breath-hold acquisition

OBJECTIVE

The purpose of this study was to ascertain whether prospective acquisition correction (PACE) diffusion-weighted MRI (DWI) is superior to conventional breath-hold DWI in assessment of split renal function.

SUBJECTS AND METHODS

Fifty-four subjects underwent coronal breath-hold DWI and PACE DWI with the b value set at 0 and 800 s/mm(2). Isotope renographic glomerular filtration rate (GFR) was used as the reference standard for assessing split renal function. A GFR of 40 mL/min or greater indicated normal and a GFR less than 40 mL/min indicated reduced split renal function. Reduced split renal function was further divided into a mild reduction group (GFR ≥ 20 mL/min) and a moderate-to-severe reduction group (GFR < 20 mL/min). Various comparisons between the imaging methods were conducted.

RESULTS

The signal-to-noise and contrast-to-noise ratios of the PACE DW images were greater than those of the breath-hold DW images (p < 0.001). The correlation between the apparent diffusion coefficient (ADC) value and GFR was stronger when the ADC was measured with PACE DWI than with breath-hold DWI (p = 0.033). Area under the receiver operator curve (AUC) analysis revealed that PACE DWI (AUC, 0.790 ± 0.045; p < 0.001) but not breath-hold DWI (AUC, 0.616 ± 0.060; p = 0.053) had diagnostic value in predicting a reduction in split renal function. ADC value assessed with PACE DWI was lower in the groups with mild and moderate-to-severe reduction in split renal function than in the group with normal function (p < 0.01).

CONCLUSION

Preliminary results imply that PACE DWI is superior to breath-hold DWI in the assessment of split renal function.

Comparison of high spatial resolution respiratory triggered inversion recovery-prepared spoiled gradient echo sequence with standard breathhold T1 sequence MRI of the liver using gadoxetic acid

PURPOSE

To assess if a high resolution respiratory triggered inversion recovery prepared GRE sequence (RT) improved image quality and detection of lesions compared with breathhold GRE T1 weighted MR sequence (BH) in the hepatobiliary uptake phase of MR of the liver using gadoxetic acid (Gd-EOB-DTPA).

MATERIALS AND METHODS

Thirty-eight consecutive patients from July 2009 to September 2010 who had undergone Gd-EOB-DTPA enhanced liver exams were retrospectively identified. Qualitative assessment performed on reference lesions and background liver by two independent readers. Quantitative assessment performed by one reader.

RESULTS

Liver parenchyma signal-to-noise ratio for BH was 90.3 ± 23.9 (mean ± SD) and RT, 106.1 ± 40.4 (P = 0.119). For BH, 320 lesions were detected compared with 257 for RT. Lesion to liver contrast was significantly better on RT sequences (0.26 ± 0.24; mean ± SD) compared with BH sequence (0.21 ± 0.20; P = 0.044). Fifty-seven reference lesions assessed. Both reviewers rated BH better for lesion margin and hepatic vessel sharpness. BH was rated with less artifact (P < 0.05). Lesion to liver contrast on BH was significantly better for one reviewer.

CONCLUSION

BH sequence had better overall image quality than RT in several quantitative and qualitative factors including number of lesions detected and level of artifact.

Comparison of breathhold, navigator-triggered, and free-breathing diffusion-weighted MRI for focal hepatic lesions

PURPOSE

To compare the breathhold, navigator-triggered, and free-breathing techniques in diffusion-weighted magnetic resonance imaging (MRI) for the evaluation of focal liver lesions on a 3.0T system.

MATERIALS AND METHODS

Fifty-two patients (36 men, 16 women; mean age, 56.4 years) with focal liver lesions underwent breathhold, navigator-triggered, and free-breathing diffusion-weighted imaging (DWI) of the liver on a 3.0 Tesla (T) system. All sequences were performed with b values of 50 and 800 s/mm(2) and identical parameters except for signal averages (two for navigator-triggered, one for breathhold, and four for free-breathing) and repetition time (3389 ms for navigator-triggered, 1500 ms for breathhold, and 4400 ms for free-breathing). A total of 74 lesions (50 malignant, 24 benign) were evaluated. The signal-to-noise ratios (SNR) of the liver and lesions, contrast-to-noise ratios (CNR) of each lesion, and ADC values of the liver and lesions were compared for each DWI sequence. The detection sensitivity and characterization accuracy were also compared.

RESULTS

The SNRs of the liver and lesions were significantly lower for breathhold DWI than for non-breathhold DWI (navigator-triggered and free-breathing DWI) for all b values. The CNRs of the lesions were also significantly lower for breathhold DWI than for non-breathhold DWI. The ADC values of the liver and focal lesions measured using the three DWI techniques were not significantly different and showed good correlation. For lesion detection and characterization, there were no significant differences between breathhold and non-breathhold DWI.

CONCLUSION

Both breathhold and non-breathhold DWI are comparable for the detection or characterization of focal liver lesions at 3.0T; however, non-breathhold DWI provides higher SNR and CNR than breathhold DWI. In addition, although free-breathing and navigator-triggered DWI sequences show similar performance for 3.0T liver imaging, free-breathing DWI is more time efficient than navigator-triggered DWI.

Liver metabolite concentrations measured with 1H MR spectroscopy

PURPOSE

To determine the feasibility of measuring choline and glycogen concentrations in normal human liver in vivo with proton (hydrogen 1 [1H]) magnetic resonance (MR) spectroscopy.

MATERIALS AND METHODS

Signed consent to participate in an institutional review board-approved and HIPAA-compliant study was obtained from 46 subjects (mean age, 46 years±17 [standard deviation]; 24 women) consecutively recruited during 285 days. Navigator-gated MR images were used to select 8-mL volumes for point-resolved spectroscopy (PRESS) with a 35-msec echo time. Line widths were minimized with fast breath-hold B0 field mapping and further manual shimming. Navigator-gated spectra were recorded with and without water suppression to determine metabolite concentrations with water signals as an internal reference. In three subjects, echo time was varied to determine the glycogen and choline T2. Linear regression analysis was used to examine relations between choline, hepatic lipid content, body mass index, glycogen content, and age.

RESULTS

Choline concentrations could be determined in 46 of 48 studies and was found to be 8.6 mmol per kilogram of wet weight±3.1 (range, 3.8-17.6; n=44). Twenty-seven spectra in 25 individuals with narrow line widths and low lipid content were adequate for quantitation of glycogen. The glycogen (glucosyl unit) concentration was 38.1 mmol/kg wet weight±14.4. The T2 of combined glycogen peaks in the liver of three subjects was 36 msec±8. Choline levels showed a weak but significant correlation with glycogen (r2=0.15; P<.05) but not with lipid content.

CONCLUSION

Navigator-gated and gradient-echo shimmed PRESS 1H MR spectroscopy may allow quantification of liver metabolites that are important for understanding and identifying disorders of glucose and lipid metabolism.

Motion-compensation techniques in neonatal and fetal MR imaging

SUMMARY

Fetal and neonatal MR imaging is increasingly used as a complementary diagnostic tool to sonography. MR imaging is an ideal technique for imaging fetuses and neonates because of the absence of ionizing radiation, the superior contrast of soft tissues compared with sonography, the availability of different contrast options, and the increased FOV. Motion in the normally mobile fetus and the unsettled, sleeping, or sedated neonate during a long acquisition will decrease image quality in the form of motion artifacts, hamper image interpretation, and often necessitate a repeat MR imaging to establish a diagnosis. This article reviews current techniques of motion compensation in fetal and neonatal MR imaging, including the following: 1) motion-prevention strategies (such as adequate patient preparation, patient coaching, and sedation, when required), 2) motion-artifacts minimization methods (such as fast imaging protocols, data undersampling, and motion-resistant sequences), and 3) motion-detection/correction schemes (such as navigators and self-navigated sequences, external motion-tracking devices, and postprocessing approaches) and their application in fetal and neonatal brain MR imaging. Additionally some background on the repertoire of motion of the fetal and neonatal patient and the resulting artifacts will be presented, as well as insights into future developments and emerging techniques of motion compensation.

Free-breathing radial 3D fat-suppressed T1-weighted gradient echo sequence: a viable alternative for contrast-enhanced liver imaging in patients unable to suspend respiration

OBJECTIVE

: To compare free-breathing radially sampled 3D fat suppressed T1-weighted gradient-echo acquisitions (radial volumetric interpolated breath-hold examination [VIBE]) with breath-hold (BH) and free-breathing conventional (rectilinearly sampled k-space) VIBE acquisitions for postcontrast imaging of the liver.

MATERIALS AND METHODS

: Eighteen consecutive patients referred for clinically indicated liver magnetic resonance imaging were imaged at 3 T. Three minutes after a single dose of gadolinium contrast injection, free-breathing radial VIBE, BH VIBE, and free-breathing VIBE with 4 averages were acquired in random order with matching sequence parameters. Radial VIBE was acquired with the "stack-of-stars" scheme, which uses conventional sampling in the slice direction and radial sampling in-plane.All image data sets were evaluated independently by 3 radiologists blinded to patient and sequence information. Each reader scored the following parameters: overall image quality, respiratory motion artifact, pulsation artifact, liver edge sharpness, and hepatic vessel clarity using a 5-point scale, with the highest score indicating the most optimum examination. Mixed model analysis of variance was used to compare sequences in terms of each measure of image quality.

RESULTS

: When scores were averaged over readers, there was no statistically significant difference between radial VIBE and BH VIBE regarding overall image quality (P = 0.1015), respiratory motion artifact (P = 1.0), and liver edge sharpness (P = 0.2955). Radial VIBE demonstrated significantly lower pulsation artifact (P < 0.0001), but had lower hepatic vessel clarity (P = 0.0176), when compared with BH VIBE. Radial VIBE had significantly higher image quality scores for all parameters when compared with free-breathing VIBE (P < 0.0001). Acquisition time for BH VIBE was 14 seconds and that of free-breathing radial VIBE and conventional VIBE with multiple averages was 56 seconds each.

CONCLUSION

: Radial VIBE can be performed during free breathing for contrast-enhanced imaging of the liver with comparable image quality to BH VIBE. However, further work is necessary to shorten the acquisition time to perform dynamic imaging.

DCE-MRI of the human kidney using BLADE: a feasibility study in healthy volunteers

PURPOSE

To evaluate the degree of motion compensation in the kidney using two different sampling methods, each in their optimized settings: A BLADE k-space acquisition technique and a routinely used kidney perfusion acquisition scheme (TurboFLASH).

MATERIALS AND METHODS

Dynamic contrast enhanced magnetic resonance examinations were performed in 16 healthy volunteers on a 3 Tesla MR-system with two parameterizations of the BLADE sequence and the standard reference acquisition scheme. Signal intensity enhanced time curves were analyzed with a mathematical model and a widely published separable compartment model on cortex regions to assess robustness versus motion artifacts.

RESULTS

BLADE-measurements with a strip-width of 32 lines constituted the smallest mean values for the sum of squared errors (6065 ± 4996) compared with the measurement with a strip-width of 64 lines (13849 ± 14079) or the standard TurboFLASH (11884 ± 8076). Calculations concerning goodness of the fit of the applied compartment model yielded an overall average of the Akaike Fit Error of 732 ± 141 for BLADE (646 ± 149 for a strip-width of 32 lines, 816 ± 53 for 64 lines) and 1626 ± 303 for the TurboFLASH (TFL) sequence.

CONCLUSION

We demonstrated that renal dynamic contrast enhanced magnetic resonance imaging using BLADE k-space sampling with a strip-width of 32 is significantly less sensitive to motion than a widely published Turbo-Flash sequence with nearly similar parameters.

Comparison of a single shot T1-weighted in- and out-of-phase magnetization prepared gradient recalled echo with a standard two-dimensional gradient recalled echo: preliminary findings

PURPOSE

To compare in-phase (IP)/out-of-phase (OP) single shot magnetization-prepared gradient-recalled-echo (MP-GRE) with a standard two-dimensional gradient-recalled-echo (2D-GRE), and to compare image quality of MP-GRE in cooperative and noncooperative subjects.

MATERIALS AND METHODS

Ninety-six consecutive subjects (52 males, 44 females; mean age, 53.2 ± 16.7 years), both cooperative (n = 73) and noncooperative (n = 23) subjects who had MRI examinations including precontrast T1-weighted IP/OP MP-GRE with or without IP/OP 2D-GRE were included in the study. The sequences were independently qualitatively evaluated by two radiologists. Quantitative analysis of liver fat index, signal-to-noise ratio (SNR) and liver-lesion contrast-to-noise ratio (CNR) was also performed. Data were subjected to statistical analysis.

RESULTS

The visual detection of the presence or absence of liver steatosis showed no differences between 2D-GRE and MP-GRE imaging (k = 1). Minor differences were observed on image quality between MP-GRE and 2D-GRE in cooperative subjects, and between MP-GRE sequences performed in cooperative and noncooperative subjects. Liver fat index results were strongly positively correlated (r = .98; 95% confidence interval [CI] 0.97 to 0.98; P < .0001). Intercept (.14; 95% CI .13 to .15; P < .0001) and slope (.83; 95% CI .79 to .86; P < .0001) were statistically significant.

CONCLUSION

IP/OP MP-GRE and 2D-GRE comparably demonstrate the presence or absence of hepatic steatosis. Image quality of MP-GRE was also comparable to 2D-GRE, and was not substantially adversely affected if subjects were unable to cooperate with breathholding instructions.