Brain magnetic resonance imaging at 3 Tesla using BLADE compared with standard rectilinear data sampling

Radiomics feature stability of open-source software evaluated on apparent diffusion coefficient maps in head and neck cancer

Radiomics is a promising technique for discovering image based biomarkers of therapy response in cancer. Reproducibility of radiomics features is a known issue that is addressed by the image biomarker standardisation initiative (IBSI), but it remains challenging to interpret previously published radiomics signatures. This study investigates the reproducibility of radiomics features calculated with two widely used radiomics software packages (IBEX, MaZda) in comparison to an IBSI compliant software package (PyRadiomics). Intensity histogram, shape and textural features were extracted from 334 diffusion weighted magnetic resonance images of 59 head and neck cancer (HNC) patients from the PREDICT-HN observational radiotherapy study. Based on name and linear correlation, PyRadiomics shares 83 features with IBEX and 49 features with MaZda, a sub-set of well correlated features are considered reproducible (IBEX: 15 features, MaZda: 18 features). We explore the impact of including non-reproducible radiomics features in a HNC radiotherapy response model. It is possible to classify equivalent patient groups using radiomic features from either software, but only when restricting the model to reliable features using a correlation threshold method. This is relevant for clinical biomarker validation trials as it provides a framework to assess the reproducibility of reported radiomic signatures from existing trials.

Free-breathing BLADE acquisition method improves T2-weighted cardiac MR image quality compared with conventional breath-hold turbo spin-echo cartesian acquisition

BACKGROUND

Cardiac magnetic resonance (MR) has become an essential diagnostic imaging modality in cardiovascular disease. However, the insufficient image quality of traditional breath-hold (BH) T2-weighted (T2W) imaging may compromise its diagnostic accuracy.

PURPOSE

To assess the efficacy of the BLADE technique to reduce motion artifacts and improve the image quality.

MATERIAL AND METHODS

Free-breathing TSE-T2W imaging sequence with cartesian and BLADE k-space trajectory were acquired in 20 patients. Thirty patients underwent conventional BH turbo spin-echo (TSE) T2W imaging and free-breathing BLADE T2W (FB BLADE-T2W) imaging. Twenty-one patients who had a signal loss of myocardium in BH short-axis T2W turbo inversion recovery (TSE-T2W-TIR) were scanned using free-breathing BLADE T2W turbo inversion recovery (BLADE TSE-T2W-TIR). The overall image quality, blood nulling, and visualization of the heart were scored on a 5-point Likert scale. The signal loss of myocardium, incomplete fat suppression near the myocardium, and the streaking or ghosting artifacts were noted in T2W-TIR sequences additionally.

RESULTS

The overall imaging quality, blood nulling, and the visualization of heart structure of FB BLADE-T2W imaging sequence were significantly better than those of FB T2W imaging with Cartesian k-space trajectory and BH TSE-T2W imaging sequence (P<0.01). The FB BLADE TSE-T2W-TIR reduces the myocardium signal dropout (P<0.05), incomplete fat suppression near myocardium (P<0.05), and the streaking and ghosting artifacts (P<0.05) in comparison with the BH TSE-T2W-TIR.

CONCLUSIONS

FB BLADE T2W imaging provides improved myocardial visibility, less motion sensitivity, and better image quality. It may be applied in patients who have poor breath-holding capability.

Chest MRI Using Multivane-XD, a Novel T2-Weighted Free Breathing MR Sequence

OBJECTIVE

To compare image quality of free-breathing T2-weighted MultiVane-XD (MVXD) sequence (non-Cartesian k-space filling using radial rectangular blades) with conventional MR sequences (short tau inversion recovery [STIR],balanced true field echo [BTFE], T1 in phase fast field echo [T1 FFE], and T1-fat saturated postgadolinium [T1PG]) in MR imaging of chest.

MATERIALS AND METHODS

Twenty-one patients (10 men and 11 women) underwent chest MRI including T2W MVXD, STIR, BTFE (18/21), T1 FFE, T1PG (10/21) sequences at 1.5 T. Two reviewers (A.S.B and M.J. with 20 and 10 years of experience in pulmonary imaging, respectively) evaluated each sequence with respect to overall image quality, image sharpness, definition of mediastinal vessels including the aorta, pulmonary arteries, superior vena cava, intrapulmonary vessels; trachea, main bronchi, intrapulmonary airways; lung-mediastinal interface, pulmonary lesion detection, and artefacts in the upper, middle, and lower third of chest using 5-point scales. No sedation was given. Pairwise comparisons between T2W MVXD and the 4 conventional sequences were made using unpaired student's t test.

RESULTS

Mean age of patients was 30.67 years (range: 6-60 years). T2 MVXD showed significantly better overall image quality and sharpness than STIR, T1 FFE, and T1PG (P < 0.01) while it was comparable to BTFE. Mediastinal vessels were significantly better visualized on T2 MVXD as compared to STIR and T1 (P < 0.003). However, BTFE and T1PG were superior to T2 MVXD for visualization of great vessels, SVC, and intrapulmonary vessels (P < 0.01). Visualization of trachea, major bronchi, intrapulmonary airways as well as intrapulmonary lesion detection was significantly better on T2 MVXD images in comparison to any of the other 4 sequences (P < 0.03). Intrapulmonary artifacts were significantly lesser in BTFE images as compared to T2 MVXD (P < 0.01). No significant difference was found between the severity of intrapulmonary artifacts in other MR sequences as compared to T2 MVXD.

CONCLUSIONS

By virtue of its better overall image quality, sharpness, superior visualization of mediastinal airways, and lesion detection, T2 MultiVane-XD promises to be a robust addition in the armamentarium of thoracic radiologists.

T1 -FLAIR imaging during continuous head motion: Combining PROPELLER with an intelligent marker

PURPOSE

The purpose of this work is to describe a T₁ -weighted fluid-attenuated inversion recovery (FLAIR) sequence that is able to produce sharp magnetic resonance images even if the subject is moving their head throughout the acquisition.

METHODS

The robustness to motion artifacts and retrospective motion correction capabilities of the PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) trajectory were combined with prospective motion correction. The prospective correction was done using an intelligent marker attached to the subject. This marker wirelessly synchronizes to the pulse sequence to measure the directionality and magnitude of the magnetic fields present in the MRI machine during a short navigator, thus enabling it to determine its position and orientation in the scanner coordinate frame. Three approaches to incorporating the marker-navigator into the PROPELLER sequence were evaluated. The specific absorption rate, and subsequent scan time, of the T₁ -weighted FLAIR PROPELLER sequence, was reduced using a variable refocusing flip-angle scheme. Evaluations of motion correction performance were done with 4 volunteers and 3 types of head motion.

RESULTS

During minimal out-of-plane movement, retrospective PROPELLER correction performed similarly to the prospective correction. However, the prospective clearly outperformed the retrospective correction when there was out-of-plane motion. Finally, the combination of retrospective and prospective correction produced the sharpest images even during large continuous motion.

CONCLUSION

Prospective motion correction of a PROPELLER sequence makes it possible to handle continuous, large, and high-speed head motions with only minor reductions in image quality.

Effectiveness of the periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) technique for reducing motion artifacts caused by mandibular movements on fat-suppressed T2-weighted magnetic resonance (MR) images

PURPOSE

To compare a fat-suppressed T2-weighted periodically rotated overlapping parallel lines with enhanced reconstruction (T2W-PROPELLER) sequence with a fat-suppressed T2-weighted fast spin-echo (T2W-FSE) sequence in the oral and maxillofacial regions for the evaluation of the presence of motion artifacts caused by mandibular movements.

METHODS

Fifty-six healthy adult volunteers were examined in a closed mouth position and then with three different rhythmical mandibular movements throughout MR scanning: open-close movement (movement 1), lateral movement (movement 2) and open-close and lateral movement (movement 3). All subjects were scanned first with fat-suppressed T2W-FSE and then with fat-suppressed T2W-PROPELLER while performing the same movements. Motion artifacts, including ghosting or pulsation artifacts, streak artifacts, susceptibility artifacts and the overall image quality were independently evaluated by two oral and maxillofacial radiologists using a five-point scale. The score graded by the two observers was averaged.

RESULTS

The inter-observer agreement was almost perfect for all evaluated items (κ ≥ 0.81). The T2W-PROPELLER images showed significantly fewer ghosting artifacts than T2W-FSE images in subjects performing the mandibular movements throughout MR scanning (P < .001). T2W-PROPELLER images also showed significantly fewer pulsation artifacts than T2W-FSE images, regardless of the performance of a movement, throughout MR scanning (P < .001). Finally, the T2W-PROPELLER images showed a significantly better overall image quality than T2W-FSE images in subjects performing movements 2 or 3 throughout MR scanning (P < .001).

CONCLUSION

The PROPELLER technique was found to be effective in reducing the motion artifacts caused by mandibular movements on fat-suppressed T2W MR images in the oral and maxillofacial regions.

Practical implications of motion correction with motion insensitive radial k-space acquisitions in MRI

OBJECTIVE

To highlight specific instances when radial k-space acquisitions in MRI result in image artifacts and how to ameliorate such artifacts.

METHODS

We acquired axial T₂ weighted MR images on (1) the American College of Radiology (ACR) phantom and (2) a sedated sheep with rectilinear and multiblade radial k-space filling acquisitions. Images were acquired on four (2 × 1.5T and 2 × 3T) different MRI scanners. For the radial k-space acquisitions, we acquired images with and without motion correction. All images were visually inspected for the presence of artifact.

RESULTS

Images collected via the conventional rectilinear method were of diagnostic quality and free of artifact. Both ACR and sheep images acquired with radial k-space acquisitions and motion correction suffered significant artifact at different slice locations, scan sessions and across all the four scanners. Severity of the artifact was associated with echo train length. However, the artifact was eliminated when motion correction was not employed.

CONCLUSION

When little to no motion is present, the use of motion correction with radial k-space acquisitions can compromise image quality. However, image quality is quickly improved, and the artifact eliminated, by repeating the scan without motion correction or by using a conventional rectilinear alternative. Advances in Knowledge: By improving awareness and understanding of this artifact, MRI users will be able to adjust MRI protocols, resulting in more successful scanning sessions, better image quality, fewer call backs and increased diagnostic confidence.

MRI of the lung using the PROPELLER technique: Artifact reduction, better image quality and improved nodule detection

PURPOSE

To evaluate the benefit of the PROPELLER technique (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction, MultiVane, MV) for MR imaging of the lung.

MATERIALS AND METHODS

30 Participants of a lung cancer screening program were recruited for the comparison of T2-MV and T2-Fast Spin Echo (FSE) sequences at 1.5T. Two readers evaluated artifacts, image quality, and pulmonary lesions. Artifacts and image quality were rated using a four-point scale. Lesion detection was correlated to low-dose computed tomography (CT). Wilcoxon rank-test for ratings of artifacts and image quality, sensitivity and specificity values for lesion detection, and Cohen's kappa for inter-rater agreement were used.

RESULTS

The MV sequence showed less pulsation and motion artifacts, and higher image quality (p=0.001 for R1, p=0.002 for R2) than FSE (p<0.001 for both readers, R1 and R2). Inter-rater agreement was excellent for lesion detection (0.84-0.95) and good to excellent for artifacts and image quality (0.66-0.84). 17 patients had lesions <8mm, and 7 had lesions >8mm as seen on CT. For R1 and R2, the MV sequence allowed for higher detection rates of pulmonary lesions <8mm with a sensitivity of 56% (R1) and 59% (R2); the FSE sequence achieved 50% (R1) and 53% (R2). Specificity was also higher for MV with 94% (R1) and 83% (R2) compared to 78% (R1) and 76% (R2). Lesions >8mm were detected with a sensitivity of 100% by both readers on both MV and FSE images. For both readers, specificity for larger lesions was higher on MV images with 100% compared to 96%.

CONCLUSION

The superior image quality and the very robust artifact reduction make MV a promising technique for MRI of the lung compared to FSE, especially since it is not requiring breathholds. Moreover, MV allows for improved lesion detection.

Detection of small brain metastases at 3 T: comparing the diagnostic performances of contrast-enhanced T1-weighted SPACE, MPRAGE, and 2D FLASH imaging

The aim of this study was to compare the diagnostic performance of contrast-enhanced T1-weighted sampling perfection with application-optimized contrasts using different flip angle evolutions (SPACE), magnetization-prepared rapid gradient-echo (MPRAGE), and two-dimensional (2D) fast low angle shot (FLASH) for the detection of small brain metastases. Twelve patients who had brain metastases less than 10 mm in diameter were enrolled. The diagnostic performance was evaluated using alternative free-response receiver operating characteristic analysis. Sensitivity and positive predictive value were also calculated. The mean Az and sensitivities of SPACE for all observers were significantly higher than those of MPRAGE and 2D FLASH.

Diffusion-weighted imaging of the sellar region: a comparison study of BLADE and single-shot echo planar imaging sequences

PURPOSE

The purpose of this study is to compare BLADE diffusion-weighted imaging (DWI) with single-shot echo planar imaging (EPI) DWI on the aspects of feasibility of imaging the sellar region and image quality.

METHODS

A total of 3 healthy volunteers and 52 patients with suspected lesions in the sellar region were included in this prospective intra-individual study. All exams were performed at 3.0T with a BLADE DWI sequence and a standard single-shot EP-DWI sequence. Phantom measurements were performed to measure the objective signal-to-noise ratio (SNR). Two radiologists rated the image quality according to the visualisation of the internal carotid arteries, optic chiasm, pituitary stalk, pituitary gland and lesion, and the overall image quality. One radiologist measured lesion sizes for detecting their relationship with the image score.

RESULTS

The SNR in BLADE DWI sequence showed no significant difference from the single-shot EPI sequence (P>0.05). All of the assessed regions received higher scores in BLADE DWI images than single-shot EP-DWI.

T2 FLAIR artifacts at 3-T brain magnetic resonance imaging

The purpose of this retrospective clinical study was to identify and evaluate the presence and frequency of T2 FLAIR artifacts on brain MRI studies performed at 3 T. We reviewed axial T2 FLAIR images in 200 consecutive unremarkable brain MRI studies performed at 3 T. All studies were reviewed for the presence of artifacts caused by pulsatile CSF flow, magnetic susceptibility and no nulling of the CSF signal. T2 FLAIR images introduce several artifacts that may degrade image quality and mimic pathology. Knowledge of these artifacts and increased severity and frequency at 3 T is of particular importance in avoiding a misdiagnosis.

Impact of field strength and RF excitation on abdominal diffusion-weighted magnetic resonance imaging

AIM: To retrospectively and prospectively compare diffusion-weighted (DW) images in the abdomen in a 1.5T system and 3.0T systems with and without two-channel functionality for B₁ shimming.

METHODS: DW images of the abdomen were obtained on 1.5T and 3.0T (with and without two-channel functionality for B₁ shimming) scanners on 150 patients (retrospective study population) and 10 volunteers (prospective study population). Eight regions were selected for clinical significance or artifact susceptibility (at higher field strengths). Objective grading quantified signal-to-noise ratio (SNR), and subjective evaluation qualified image quality, ghosting artifacts, and diagnostic value. Statistical significance was calculated using χ² tests (categorical variables) and independent two-sided t tests or Mann-Whitney U tests (continuous variables).

RESULTS: The 3.0T using dual-source parallel transmit (dpTX 3.0T) provided the significantly highest SNRs in nearly all regions. In regions susceptible to artifacts at higher field strengths (left lobe of liver, head of pancreas), the SNR was better or similar to the 1.5T system. Subjectively, both dpTX 3.0T and 1.5T systems provided higher image quality, diagnostic value, and less ghosting artifact (P < 0.01, most values) compared to the 3.0T system without dual-source parallel transmit (non-dpTX 3.0T).

CONCLUSION: The dpTX 3.0T scanner provided the highest SNR. Its image quality, lack of ghosting, and diagnostic value were equal to or outperformed most currently used systems.

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.

Novel application of T1-weighted BLADE sequences with fat suppression compared to TSE in contrast-enhanced T1-weighted imaging of the neck: cutting-edge images?

PURPOSE

To evaluate if the use of BLADE sequences might overcome some limitations of magnetic resonance imaging (MRI) in the extracranial head and neck, which is a diagnostically challenging area with a variety of artifacts and a broad spectrum of potential lesions.

MATERIALS AND METHODS

After informed consent and Institutional Review Board approval, two different BLADE sequences with (BLADE IR) and without inversion pulse (BLADE) were compared to turbo-spin echo (TSE) with fat saturation for coronal T1-weighted postcontrast imaging of the extracranial head and neck region in 40 individuals of a routine patient collective. Visual evaluation of image sharpness, motion artifacts, vessel pulsation, contrast of anatomic structures, contrast of pathologies to surrounding tissue as well as BLADE-specific artifacts was performed by two experienced, independent readers. Statistical evaluation was done by using the Wilcoxon test.

RESULTS

Both BLADE and BLADE IR were significantly superior to TSE regarding pulsation artifacts and delineation of thoracic structures. TSE provided better results concerning contrast muscle/fat tissue and contrast lymph nodes/fat. More important, it showed significantly better contrast of several lesions, facilitating the detection of patient pathology.

CONCLUSION

T1-weighted coronal imaging of the extracranial head and neck region is demanding. T1-weighted BLADE sequences still have drawbacks in anatomical contrast and lesion detection but offer possibilities to achieve reasonable image quality in difficult cases with a variety of artifacts.

Should less motion sensitive T2-weighted BLADE TSE replace Cartesian TSE for female pelvic MRI?

Objectives

To prospectively compare the diagnostic performance of a non-Cartesian k-space sampling T2-weighted TSE BLADE sequence with a conventional T2-weighted TSE sequence in female pelvic organs.

Methods

Forty-seven patients with sonographically indeterminate adnexal masses or uterine lesions underwent sagittal BLADE and conventional TSE at 1.5 T after glucagon administration. Two radiologists independently determined their preferred sequence by rating: overall image diagnostic quality, conspicuity of the zonal anatomy and delineation of pathologies of the uterus and cervix, presence of artefacts, and of fluid in the pouch of Douglas (Wilcoxon signed rank test). Signal-to noise ratios (SNRs) and contrast-to-noise ratios (CNRs) were measured for the myometrium versus the rectus abdominis muscle (Student’s t-test).

Results

BLADE significantly (p < 0.0001) reduced motion and ghosting artefacts and showed improved conspicuity (p = 0.3/0.24), but overall image quality did not differ significantly (inter-observer agreement BLADE κ = 0.89; TSE κ = 0.84). In the majority of cases (53.2 % vs 59.6 %, respectively, κ = 0.82) radiologists preferred conventional TSE due to better image contrast (p < 0.0001) and visibility of free pelvic fluid (p ≤ 0.0001). SNR (TSE 57.5 ± 37.7; BLADE 16.6 ± 12.2) and CNR (TSE 40.4 ± 33.5; BLADE 7.2 ± 8.8) were significantly higher on conventional TSE (p < 0.0001).

Conclusions

Although BLADE reduces motion artefacts and provides a clearer delineation of uterine zonal anatomy compared with conventional TSE, this comes at the expense of overall contrast.

Main Messages

• Use of BLADE may reduce T2 contrast and thus visibility of free pelvic fluid or cystic structures

• Non-Cartesian sampling of k-space such as BLADE is beneficial due to less motion sensitivity

• BLADE provides clearer delineation and conspicuity of uterine zonal anatomy on pelvic MRIs

Effective performance of T(1)-weighted FLAIR Imaging with BLADE in pediatric brains

PURPOSE

In magnetic resonance imaging of the brain, BLADE is used to compensate for head motion. The technique focuses mainly on acquisition of T(2)-weighted or contrast-enhanced T(1)-weighted images in adults; its utility for nonenhanced T(1)-weighted imaging in children is not well established. We compared the quality of T(1)-weighted fluid-attenuated inversion recovery brain imaging with BLADE (T(1)-FLAIR-BLADE) to that of conventional spin-echo T(1)-weighted imaging (T(1)-SE) in pediatric patients who cannot stay still during MR imaging.

MATERIALS AND METHODS

Our investigation included a volunteer study and a retrospective clinical study. Six healthy adult volunteers underwent scanning to compare the contrast of T(1)-SE, T(1)-weighted fluid-attenuated inversion recovery imaging (T(1)-FLAIR), and T(1)-FLAIR-BLADE at both 1.5 and 3 tesla. Comparison was based on scores assigned independently by 2 blinded observers and by calculated contrast-to-noise ratio. The clinical study included 20 children who underwent both T(1)-SE and T(1)-FLAIR-BLADE at either 1.5 (n = 9) or 3 T (n = 11). On each sequence, 2 blinded observers independently scored visualization of the cerebral gyri and contrast between gray and white matter. We compared scores between sequences separately for 1.5 and 3T using Wilcoxon signed-rank tests.

RESULTS

At both 1.5 and 3T, contrast was better using T(1)-FLAIR and T(1)-FLAIR-BLADE than T(1)-SE in volunteers, and overall scores were significantly higher with T(1)-FLAIR-BLADE (P < 0.05) than T(1)-SE in the clinical study.

CONCLUSION

T(1)-FLAIR-BLADE may be superior to T(1)-SE in demonstrating brain structures in children who cannot stay still and may be used to supplement or replace T(1)-SE when T(1)-SE is insufficient for patient motion.

3D fluid-attenuated inversion recovery imaging: reduced CSF artifacts and enhanced sensitivity and specificity for subarachnoid hemorrhage

BACKGROUND AND PURPOSE

FLAIR images are highly sensitive for SAH. However, CSF flow artifacts caused by conventional FLAIR can produce false-positive results. Here, we compare 3D and 3D FLAIR sequences, focusing on their potential for containing these artifacts and their sensitivity and specificity for detection of SAHs.

MATERIALS AND METHODS

We evaluated the following 4 FLAIR sequences: 1) 2D FLAIR at 1.5T, 2) 2D FLAIR, 3) 2D PROPELLER-FLAIR, and 4) 3D Cube-FLAIR at 3T. All sequences were performed in 5 healthy volunteers; sequences 2 and 4 were also performed under routine conditions in 10 patients with focal epilepsy and in 10 patients with SAH. Two neuroradiologists independently conducted the analysis. The presence of flow artifacts in the ventricles and cisterns of healthy volunteers and patients with epilepsy was evaluated and scored on a 4-point scale. Mean values were calculated and compared by using paired t tests. Sensitivity and specificity for SAH detection in sequences 2 and 4 were determined.

RESULTS

Cube-FLAIR showed almost no CSF artifacts in the volunteers and the patients with epilepsy; therefore, it was superior to any other FLAIR (P < .001). Sensitivity and specificity of SAH detection by 3T FLAIR were 58.3% and 89.4%, respectively, whereas Cube-FLAIR had a sensitivity of 95% and a specificity of 100%.

CONCLUSIONS

Cube-FLAIR allows FLAIR imaging with almost no CSF artifacts and is, thus, particularly useful for SAH detection.

Comparison of brain MR images at 1.5T using BLADE and rectilinear techniques for patients who move during data acquisition

BACKGROUND AND PURPOSE

MR imaging of moving patients can be challenging and motion correction techniques have been proposed though some have associated new artifacts. The objective of this study was to semiquantitatively compare brain MR images of moving patients obtained at 1.5T by using partially radial and rectilinear acquisition techniques.

MATERIALS AND METHODS

FLAIR, T2-, T1-, and contrast-enhanced T1-weighted image sets of 25 patients (14-94 years) obtained by using BLADE (like PROPELLER, a partially radial acquisition) and rectilinear techniques in the same imaging session were compared by 2 neuroradiologists in terms of extent of the motion artifact, image quality, and lesion visibility. ICC between opinions of the evaluators was calculated.

RESULTS

Of the total of 70 image sets, the motion artifact was small in the partially radial images in 43 and in the rectilinear images in 13, and the opinions of the evaluators were discordant in the remaining 14 sets (ICC = 0.63, P < .05). The quality of partially radial images was higher for 36 sets versus 9 rectilinear sets, with disagreement between the 2 evaluators in the remaining 25 (ICC = 0.15, P < .05). Pathologic lesions were better characterized on 37 sets of partially radial images versus 13 sets of rectilinear images, and opinions of the evaluators differed in 20 sets (ICC = 0.90, P < .05). The neuroradiologists deemed 4 sets of rectilinear images nondiagnostic compared with only 1 set of radial images.

CONCLUSIONS

The data demonstrate that our application of BLADE sequences reduces the extent of motion artifacts in brain images of moving patients, improving image quality and lesion characterization.

An image-based approach to understanding the physics of MR artifacts

As clinical magnetic resonance (MR) imaging becomes more versatile and more complex, it is increasingly difficult to develop and maintain a thorough understanding of the physical principles that govern the changing technology. This is particularly true for practicing radiologists, whose primary obligation is to interpret clinical images and not necessarily to understand complex equations describing the underlying physics. Nevertheless, the physics of MR imaging plays an important role in clinical practice because it determines image quality, and suboptimal image quality may hinder accurate diagnosis. This article provides an image-based explanation of the physics underlying common MR imaging artifacts, offering simple solutions for remedying each type of artifact. Solutions that have emerged from recent technologic advances with which radiologists may not yet be familiar are described in detail. Types of artifacts discussed include those resulting from voluntary and involuntary patient motion, magnetic susceptibility, magnetic field inhomogeneities, gradient nonlinearity, standing waves, aliasing, chemical shift, and signal truncation. With an improved awareness and understanding of these artifacts, radiologists will be better able to modify MR imaging protocols so as to optimize clinical image quality, allowing greater confidence in diagnosis.

Breath-hold T2-weighted MRI of the liver at 3T using the BLADE technique: impact upon image quality and lesion detection

AIM

To compare image quality and lesion detection in the liver using magnetic resonance imaging (MRI) at 3T between T2-weighted imaging using a standard rectilinear k-space trajectory (standard T2WI) and using the BLADE technique (BLADE-T2WI), a technique that employs periodically rotated overlapping parallel lines with enhanced reconstruction for motion correction.

MATERIALS AND METHODS

Twenty-eight consecutive patients who underwent MRI examination of the liver at 3T including standard T2WI and BLADE-T2WI, both performed using multiple breath-holds, comprised the study cohort. Images were reviewed in consensus by two radiologists during separate sessions for a number of measures regarding artefacts and image quality. These two readers also assessed the two image sets for the presence of liver lesions and measured liver-to-lesion contrast. Binary logistic regression for correlated data was used to compare the sequences in terms of sensitivity and positive predictive value (PPV) for lesion detection.

RESULTS

BLADE-T2WI received significantly higher scores than did standard T2WI for in-plane respiratory motion (p=0.0195), other ghosting artefacts (p<0.0001), sharpness of the liver edge (p=0.0004), sharpness of intra-hepatic vessels (p<0.0001), flow signal suppression (p<0.0001), and overall image quality (p<0.0001). There was a non-significant trend toward improved B(1)-inhomogeneity artefact with BLADE-T2WI (p=0.0571). There was no difference in through-plane respiratory motion (p=0.6836). BLADE-T2WI demonstrated a significant improvement in PPV for lesion detection (p=0.0129) as well as in liver-to-lesion contrast (p=0.0054). There was no difference regarding lesion sensitivity (p=1.0).

CONCLUSIONS

Use of the BLADE technique for T2-weighted MRI of the liver at 3T may lead to a significant improvement in image artefacts and improved PPV for lesion detection.

PROPELLER for motion-robust imaging of in vivo mouse abdomen at 9.4 T

In vivo high-field MRI in the abdomen of small animals is technically challenging because of the small voxel sizes, short T(2) and physiological motion. In standard Cartesian sampling, respiratory and gastrointestinal motion can lead to ghosting artefacts. Although respiratory triggering and navigator echoes can either avoid or compensate for motion, they can lead to variable TRs, require invasive intubation and ventilation, or extend TEs. A self-navigated fast spin echo (FSE)-based periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) acquisition was implemented at 9.4 T to enable high-resolution in vivo MRI of mouse abdomen without the use of additional navigators or triggering. T(2)-weighted FSE-PROPELLER data were compared with single-shot FSE and multi-shot FSE data with and without triggering. Single-shot methods, although rapid and robust to motion, demonstrated strong blurring. Multi-shot FSE data showed better resolution, but suffered from marked blurring in the phase-encoding direction and motion in between shots, leading to ghosting artefacts. When respiratory triggering was used, motion artefacts were largely avoided. However, TRs and acquisition times were lengthened by up to approximately 20%. The PROPELLER data showed a 25% and 61% improvement in signal-to-noise ratio and contrast-to-noise ratio, respectively, compared with multi-shot FSE data, together with a 35% reduction in artefact power. A qualitative comparison between acquisition methods using diffusion-weighted imaging was performed. The results were similar, with the exception that respiratory triggering was unable to exclude major motion artefacts as a result of the sensitisation to motion by the diffusion gradients. The PROPELLER data were of consistently higher quality. Considerations specific to the use of PROPELLER at high field are discussed, including the selection of practical blade widths and the effects on contrast, resolution and artefacts.

Evaluation of gadobutrol, a macrocyclic, nonionic gadolinium chelate in a brain glioma model: comparison with gadoterate meglumine and gadopentetate dimeglumine at 1.5 T, combined with an assessment of field strength dependence, specifically 1.5 versus 3 T

PURPOSE

To evaluate in a rat brain glioma model intraindividual tumor enhancement at 1.5 T using gadobutrol (Gadovist), a nonionic, macrocyclic chelate currently in clinical trials in the United States, in comparison with both an ionic macrocyclic chelate, gadoterate meglumine (Dotarem), and an ionic linear chelate, gadopentetate dimeglumine (Magnevist), and to compare the degree of tumor enhancement with gadobutrol at 1.5 and 3 T.

MATERIALS AND METHODS

A total of 24 rats, divided into three groups with n = 8 animals per group, were evaluated. Animals in group 1 received injections of gadobutrol and gadopentetate dimeglumine, whereas those in group 2 received gadobutrol and gadoterate meglumine. Injections were performed in random order and separated by 24 hours. Magnetic resonance imaging (MRI) examinations were performed immediately following each contrast injection with a 1.5 T MR system. Animals in group 3 received gadobutrol injections using the same protocol but with scans performed at 1.5 and 3 T. In all examinations, T1-weighted images were acquired precontrast, 1 minute postcontrast, and at 4 consecutive 2-minute intervals thereafter. A contrast dose of 0.1 mmol/kg was used in all instances.

RESULTS

In groups 1 and 2, tumor signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were higher for gadobutrol compared to both other agents at each timepoint postcontrast injection. The improvement in tumor CNR with gadobutrol, depending on time, was between 12% and 40% versus gadopentetate dimeglumine, with the difference achieving statistical significance at 7 minutes. The improvement in tumor CNR with gadobutrol, depending on time, was between 15% and 27% versus gadoterate meglumine, with the difference statistically significant at 5 and 9 minutes. In group 3 the improvement in tumor SNR and CNR seen with the increase in field strength from 1.5 to 3 T for gadobutrol was statistically significant at all acquired timepoints (P < 0.002). CNR mean values ranged from 10.4 +/- 2.9 to 24.6 +/- 5.0 at 1.5 T and from 20.5 +/- 5.9 to 47.8 +/- 15.7 at 3 T depending on the timepoint postcontrast.

CONCLUSION

Consistently greater tumor enhancement was noted at all measured timepoints following contrast injection with gadobutrol compared to both gadopentetate dimeglumine and gadoterate meglumine at 1.5 T. A substantial further improvement in tumor enhancement was noted using gadobutrol at 3 T.

Diagnostic value of T2-weighted imaging for the detection of superficial cranial artery inflammation in giant cell arteritis

PURPOSE

To evaluate the diagnostic value of T2-weighted radial MR imaging for the detection of superficial cranial arteries' inflammatory involvement in patients with giant cell arteritis (GCA).

MATERIALS AND METHODS

Forty-three patients with suspected giant cell arteritis underwent 3 Tesla (T) high-field MRI. T2-weighted inversion recovery (IR) fast spin echo images with radial sampling (BLADE-technique) were acquired and compared with postcontrast T1-weighted spin echo images.

RESULTS

T2-weighted images revealed mural edema in the superficial cranial arteries in 11 patients in concordance with severe inflammatory contrast enhancement in T1-weighted images (grade 4 in a 4-point ranking scale). Excellent correlation (r = 0.82; P < 0.001) of measured wall thickness in T1- and T2-weighted images was achieved.

CONCLUSION

The results of this study indicate the potential of radial T2 weighted imaging for a first detection of inflammatory changes in the small superficial cranial arteries without the need for contrast medium. Future studies are needed to evaluate the influence of spatial resolution of the T2 images and to improve the detection of moderate GCA related changes in vessel inflammation.

T2-weighted MRI of the upper abdomen: comparison of four fat-suppressed T2-weighted sequences including PROPELLER (BLADE) technique

RATIONALE AND OBJECTIVES

The aim of this study was to compare four different fat-suppressed T2-weighted sequences with different techniques with regard to image quality and lesion detection in upper abdominal magnetic resonance imaging (MRI) scans.

MATERIALS AND METHODS

Thirty-two consecutive patients referred for upper abdominal MRI for the evaluation of various suspected pathologies were included in this study. Different T2-weighted sequences (free-breathing navigator-triggered turbo spin-echo [TSE], free-breathing navigator-triggered TSE with restore pulse (RP), breath-hold TSE with RP, and free-breathing navigator-triggered TSE with RP using the periodically rotated overlapping parallel lines with enhanced reconstruction technique [using BLADE, a Siemens implementation of this technique]) were used on all patients. All images were assessed independently by two radiologists. Assessments of motion artifacts; the edge sharpness of the liver, pancreas, and intrahepatic vessels; depictions of the intrahepatic vessels; and overall image quality were performed qualitatively. Quantitative analysis was performed by calculation of the signal-to-noise ratios for liver tissue and gallbladder as well as contrast-to-noise ratios of liver to spleen.

RESULTS

Liver and gallbladder signal-to-noise ratios as well as liver to spleen contrast-to-noise ratios were significantly higher (P < .05) for the BLADE technique compared to all other sequences. In qualitative analysis, the severity of motion artifacts was significantly lower with T2-weighted free-breathing navigator-triggered BLADE sequences compared to other sequences (P < .01). The edge sharpness of the liver, pancreas, and intrahepatic vessels; depictions of the intrahepatic vessels; and overall image quality were significantly better with the BLADE sequence (P < .05).

CONCLUSION

The T2-weighted free-breathing navigator-triggered TSE sequence with the BLADE technique is a promising approach for reducing motion artifacts and improving image quality in upper abdominal MRI scans.

The value of different magnetic resonance imaging sequences for the detection of intraventricular hemorrhages*

PURPOSE

The aim of this study was to determine the value of different magnetic resonance imaging (MRI) sequences for the diagnosis of intraventricular hemorrhages (IVHs).

PATIENTS AND METHODS

The study included 22 consecutive patients with computed tomography (CT) proven IVH in which an MR examination had been performed. Proton-density-(PD-), T2-, fluid-attenuated inversion-recovery (FLAIR), T1- and T2*-weighted images were evaluated retrospectively by two neuroradiologists regarding presence and anatomical distribution of IVH, and cerebrospinal fluid (CSF) flow artifacts. CT was used as gold standard.

RESULTS

According to CT, IVH was located in the right/left lateral ventricles in 16/17 patients, in the third ventricle in seven and in the fourth ventricle in twelve cases. PD- and T2*-weighted images both showed a 100% sensitivity and specificity for the overall diagnosis of IVH, and a high sensitivity for the detection of IVH in all four ventricles. The sensitivity of T1-, T2- and FLAIR- weighted images for the overall presence of an IVH was 77%, 85%, and 93%, respectively, with specificities of 100%. CSF flow artifacts occurred predominantly in the third and fourth ventricles. While FLAIR- and T2-weighted sequences were especially prone to this phenomenon, T1-, T2*- and PD-weighted images showed a higher resistance to those artifacts.

CONCLUSION

This study demonstrates a high sensitivity of PD- and T2*-weighted images in the detection of IVH. On the contrary, T2-, T1- and FLAIR-weighted sequences were not suitable for a reliable detection of IVH.

Diffusion-weighted imaging in head and neck cancers

This article reviews the utility of diffusion-weighted imaging (DWI) in the diagnosis, prognosis and monitoring of treatment response in tumors arising in the head and neck region. The apparent diffusion coefficient (ADC) value, determined from DWI, can help in cancer staging and detection of subcentimeter nodal metastasis. The ADC value also discriminates carcinomas from lymphomas, benign lesions from malignant tumors and tumor necrosis from abscesses. Low pretreatment ADC values typically predict a favorable response to chemoradiation therapy. These promising reports indicate the potential of DWI as a potential biomarker for diagnosis and monitoring of treatment response in head and neck cancers. In view of the overlapping ADC values between different salivary gland tumors, care should be taken when interpreting these results and other imaging parameters should be considered for a better diagnosis. Susceptibility and motion-induced artifacts may sometimes degrade DWI image quality; however, novel techniques are being developed to overcome these drawbacks.

BLADE in sagittal T2-weighted MR imaging of the cervical spine

BACKGROUND AND PURPOSE

Image quality and diagnostic reliability of T2-weighted MR images of the cervical spine are often impaired by several kinds of artifacts, even in cooperative patients. The aim of this study was to evaluate if BLADE sequences might solve these problems in a routine patient collective.

MATERIALS AND METHODS

TSE and BLADE sequences were compared in 60 patients for T2-weighted sagittal imaging of the cervical spine. Image sharpness, motion artifacts, truncation artifacts, metal artifacts, CSF flow phenomena, contrast of anatomic structures (vertebral body/disk, spinal cord/CSF), and diagnostic reliability of spinal cord depiction were evaluated by 2 independent readers. Another 2 readers selected the sequence they would prefer for diagnostic purposes. Statistical evaluations were performed by using the Wilcoxon and the chi(2) test; differences with P < .05 were regarded as statistically significant.

RESULTS

BLADE was significantly superior to TSE regarding image sharpness, image contrast, diagnostic reliability of spinal cord depiction, motion artifacts, CSF flow phenomena, and truncation artifacts; for metal artifacts no significant improvements were found. In 50 of 60 patients, BLADE was preferred for diagnostic purposes, and TSE was favored in 3 patients. The number of examinations that were nondiagnostic due to impaired spinal cord depiction was reduced from 12 in TSE to 3 in BLADE, and nondiagnostic examinations due to overall motion artifacts were reduced from 2 to 1.

CONCLUSIONS

Using the BLADE sequence for sagittal T2-weighted imaging of the cervical spine proved to be advantageous to reduce various kinds of artifacts.

Reduced artefacts and improved assessment of hyperintense brain lesions with BLADE MR imaging in patients with neurofibromatosis type 1

BACKGROUND

Assessment of small brain lesions in children is often compromised by pulsation, flow or movement artefacts. MRI with a rotating blade-like k-space covering (BLADE, PROPELLER) can compensate for these artefacts.

OBJECTIVE

We compared T2-weighted FLAIR images that were acquired with different k-space trajectories (conventional Cartesian and BLADE) to evaluate the impact of BLADE technique on the delineation of small or low-contrast brain lesions.

MATERIALS AND METHODS

The subject group comprised 26 children with neurofibromatosis type 1 (NF 1), who had been routinely scanned at 1.5 T for optic pathway gliomas with both techniques and who had the typical hyperintense brain lesions seen in NF 1. Four experienced radiologists retrospectively compared unlabelled 4-mm axial images with respect to the presence of artefacts, visibility of lesions, quality of contour and contrast.

RESULTS

Both techniques were comparable in depicting hyperintense lesions as small as 2 mm independent of contrast and edge definition. Pulsation and movement artefacts were significantly less common with BLADE k-space trajectory. In 7 of 26 patients (27%), lesions and artefacts were rated as indistinguishable in conventional FLAIR, but not in BLADE FLAIR images.

CONCLUSION

BLADE imaging significantly improved the depiction of lesions in T2-W FLAIR images due to artefact reduction especially in the posterior fossa.

Performance of PROPELLER relative to standard FSE T2-weighted imaging in pediatric brain MRI

BACKGROUND

T2-weighted fast spin-echo imaging (T2-W FSE) is frequently degraded by motion in pediatric patients. MR imaging with periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) employs alternate sampling of k-space to achieve motion reduction.

OBJECTIVE

To compare T2-W PROPELLER FSE (T2-W PROP) with conventional T2-W FSE for: (1) image quality; (2) presence of artefacts; and (3) ability to detect lesions.

MATERIALS AND METHODS

Ninety-five pediatric patients undergoing brain MRI (1.5 T) were evaluated with T2-W FSE and T2-W PROP. Three independent radiologists rated T2-W FSE and T2-W PROP, assessing image quality, presence of artefacts, and diagnostic confidence. Chi-square analysis and Wilcoxon signed rank test were used to assess the radiologists' responses.

RESULTS

Compared with T2-W FSE, T2-W PROP demonstrated better image quality and reduced motion artefacts, with the greatest benefit in children younger than 6 months. Although detection rates were comparable for the two sequences, blood products were more conspicuous on T2-W FSE. Diagnostic confidence was higher using T2-W PROP in children younger than 6 months. Average inter-rater agreement was 87%.

CONCLUSION

T2-W PROP showed reduced motion artefacts and improved diagnostic confidence in children younger than 6 months. Thus, use of T2-W PROP rather than T2-W FSE should be considered in routine imaging of this age group, with caution required in identifying blood products.

Multishot targeted PROPELLER magnetic resonance imaging: description of the technique and initial applications

OBJECTIVES

To test the feasibility of combining inner-volume imaging (IVI) techniques with conventional multishot periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) techniques for targeted-PROPELLER magnetic resonance imaging.

MATERIALS AND METHODS

Perpendicular section-selective gradients for spatially selective excitation and refocusing RF pulses were applied to limit the refocused field-of-view (FOV) along the phase-encoding direction for each rectangular blade image. We performed comparison studies in phantoms and normal volunteers by using targeted-PROPELLER methods for a wide range of imaging applications that commonly use turbo-spin-echo (TSE) approaches (brain, abdominal, vessel wall, cardiac).

RESULTS

In these initial studies, we demonstrated the feasibility of using targeted-PROPELLER approaches to limit the imaging FOV thereby reducing the number of blades or permitting increased spatial resolution without commensurate increases in scan time. Both phantom and in vivo motion studies demonstrated the potential for more robust regional self-navigated motion correction compared with conventional full FOV PROPELLER methods.

CONCLUSION

We demonstrated that the reduced FOV targeted-PROPELLER technique offers the potential for reducing imaging time, increasing spatial resolution, and targeting specific areas for robust regional motion correction.

Contrast-enhanced MR imaging of metastatic brain tumor at 3 tesla: utility of T(1)-weighted SPACE compared with 2D spin echo and 3D gradient echo sequence

We evaluated the newly developed whole-brain, isotropic, 3-dimensional turbo spin-echo imaging with variable flip angle echo train (SPACE) for contrast-enhanced T(1)-weighted imaging in detecting brain metastases at 3 tesla (T). Twenty-two patients with suspected brain metastases underwent postcontrast study with SPACE, magnetization-prepared rapid gradient-echo (MP-RAGE), and 2-dimensional T(1)-weighted spin echo (2D-SE) imaging at 3T. We quantitatively compared SPACE, MP-RAGE, and 2D-SE images by using signal-to-noise ratios (SNRs) for gray matter (GM) and white matter (WM) and contrast-to-noise ratios (CNRs) for GM-to-WM, lesion-to-GM, and lesion-to-WM. Two blinded radiologists evaluated the detection of brain metastases by segment-by-segment analysis and continuously-distributed test. The CNR between GM and WM was significantly higher on MP-RAGE images than on SPACE images (P<0.01). The CNRs for lesion-to-GM and lesion-to-WM were significantly higher on SPACE images than on MP-RAGE images (P<0.01). There was no significant difference in each sequence in detection of brain metastases by segment-by-segment analysis and the continuously-distributed test. However, in some cases, the lesions were easier to detect in SPACE images than in other sequences, and also the vascular signals, which sometimes mimic lesions in MP-RAGE and 2D-SE images, were suppressed in SPACE images. In detection of brain metastases at 3T magnetic resonance (MR) imaging, SPACE imaging may provide an effective, alternative approach to MP-RAGE imaging for 3D T(1)-weighted imaging.

Contrast-enhanced T1-weighted fluid-attenuated inversion-recovery BLADE magnetic resonance imaging of the brain: an alternative to spin-echo technique for detection of brain lesions in the unsedated pediatric patient?

RATIONALE AND OBJECTIVES

We compared contrast-enhanced T1-weighted magnetic resonance (MR) imaging of the brain using different types of data acquisition techniques: periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER, BLADE) imaging versus standard k-space sampling (conventional spin-echo pulse sequence) in the unsedated pediatric patient with focus on artifact reduction, overall image quality, and lesion detectability.

MATERIALS AND METHODS

Forty-eight pediatric patients (aged 3 months to 18 years) were scanned with a clinical 1.5-T whole body MR scanner. Cross-sectional contrast-enhanced T1-weighted spin-echo sequence was compared to a T1-weighted dark-fluid fluid-attenuated inversion-recovery (FLAIR) BLADE sequence for qualitative and quantitative criteria (image artifacts, image quality, lesion detectability) by two experienced radiologists. Imaging protocols were matched for imaging parameters. Reader agreement was assessed using the exact Bowker test.

RESULTS

BLADE images showed significantly less pulsation and motion artifacts than the standard T1-weighted spin-echo sequence scan. BLADE images showed statistically significant lower signal-to-noise ratio but higher contrast-to-noise ratios with superior gray-white matter contrast. All lesions were demonstrated on FLAIR BLADE imaging, and one false-positive lesion was visible in spin-echo sequence images.

CONCLUSION

BLADE MR imaging at 1.5 T is applicable for central nervous system imaging of the unsedated pediatric patient, reduces motion and pulsation artifacts, and minimizes the need for sedation or general anesthesia without loss of relevant diagnostic information.