MRI of the pelvis at 3 T: very high spatial resolution with sensitivity encoding and flip-angle sweep technique in clinically acceptable scan time

High Acceleration Three-Dimensional T1-Weighted Dual Echo Dixon Hepatobiliary Phase Imaging Using Compressed Sensing-Sensitivity Encoding: Comparison of Image Quality and Solid Lesion Detectability with the Standard T1-Weighted Sequence

Objective

To compare a high acceleration three-dimensional (3D) T1-weighted gradient-recalled-echo (GRE) sequence using the combined compressed sensing (CS)-sensitivity encoding (SENSE) method with a conventional 3D GRE sequence using SENSE, with respect to image quality and detectability of solid focal liver lesions (FLLs) in the hepatobiliary phase (HBP) of gadoxetic acid-enhanced liver MRI.

Materials and Methods

A total of 217 patients with gadoxetic acid-enhanced liver MRI at 3T (54 in the preliminary study and 163 in the main study) were retrospectively included. In the main study, HBP imaging was done twice using the standard mDixon-3D-GRE technique with SENSE (acceleration factor [AF]: 2.8, standard mDixon-GRE) and the high acceleration mDixon-3D GRE technique using the combined CS-SENSE technique (CS-SENSE mDixon-GRE). Two abdominal radiologists assessed the two MRI data sets for image quality in consensus. Three other abdominal radiologists independently assessed the diagnostic performance of each data set and its ability to detect solid FLLs in 117 patients with 193 solid nodules and compared them using jackknife alternative free-response receiver operating characteristics (JAFROC).

Results

There was no significant difference in the overall image quality. CS-SENSE mDixon-GRE showed higher image noise, but lesser motion artifact levels compared with the standard mDixon-GRE (all p < 0.05). In terms of lesion detection, reader-averaged figures-of-merit estimated with JAFROC was 0.918 for standard mDixon-GRE, and 0.953 for CS-SENSE mDixon-GRE (p = 0.142). The non-inferiority of CS-SENSE mDixon-GRE over standard mDixon-GRE was confirmed (difference: 0.064 [−0.012, 0.081]).

Conclusion

The CS-SENSE mDixon-GRE HBP sequence provided comparable overall image quality and non-inferior solid FFL detectability compared with the standard mDixon-GRE sequence, with reduced acquisition time.

Ultrasonography-Based Qualitative and Quantitative Evaluation Approaches for Pompe Disease

Purpose

The aim of this study was to propose the qualitative and quantitative approaches to evaluate the skeletal muscle ultrasound images of 23 Pompe disease (i.e., acid maltase deficiency, AMD) patients and 14 normal subjects.

Methods

A cohort of 23 AMD patients and 14 normal subjects has been investigated. We compared the B-mode echo intensity of the rectus femoris muscle with that of its surrounding fat (subcutaneous fat) and proposed a qualitative grading method. Quantitative analysis of the region of interest (ROI) with the echo intensity and the segmented area was also performed.

Results

Qualitative results showed that AMD patients without clinical symptoms (without undergoing ERT) had the highest distribution of Grade 1, and AMD patients undergoing ERT had the widest distribution of Grade 2, and control group (n = 14) with the highest distribution of Grade 1. Using the segmented area approach, quantitative results showed that AMD patients undergoing ERT had the largest and widest distribution. Meanwhile the control subjects (normal subjects) had the lowest and the narrowest areas. The echo intensity of the segmented ROI of AMD patients undergoing ERT displayed the highest and widest (inhomogeneous) distributions. By contrast, the echo intensity of AMD patients without clinical symptoms was slightly increased and with low inhomogeneity.

Conclusion

The proposed ultrasonography-based qualitative and quantitative approach may be used to evaluate the severity of muscle destruction for AMD patients. Besides, the quantitative segmented area with regression analysis could help predict the incidence of onset of Pompe disease patients.

Gray-matter-specific MR imaging improves the detection of epileptogenic zones in focal cortical dysplasia: A new sequence called fluid and white matter suppression (FLAWS)

Objectives

To evaluate the diagnostic value and characteristic features of FCD epileptogenic zones using a novel sequence called fluid and white matter suppression (FLAWS).

Materials and methods

Thirty-nine patients with pathologically confirmed FCD and good surgery outcomes (class I or II, according to the Engel Epilepsy Surgery Outcome Scale) were retrospectively included in the study. All the patients underwent a preoperative whole-brain MRI examination that included conventional sequences (T2WI, T1WI, two-dimensional (2D) axial, coronal fluid-attenuated inversion recovery [FLAIR]) and FLAWS. An additional 3D-FLAIR MRI sequence was performed in 17 patients. To evaluate the sensitivity and specificity of FLAWS and investigate the cause of false-positives, 36 healthy volunteers were recruited as normal controls. Two radiologists evaluated all the image data. The detection rates of the FCD epileptogenic zone on different sequences were compared based on five criteria: abnormal cortical morphology (thickening, thinning, or abnormally deep sulcus); abnormal cortical signal intensity; blurred gray-white matter junction; abnormal signal intensity of the subcortical white matter, and the transmantle sign. The sensitivity and specificity of FLAWS for detecting the FCD lesions were calculated with the reviewers blinded to all the clinical information, i.e. to the patient identity and the location of the resected regions. To explore how many features were sufficient for the diagnosis of the epileptogenic zones, the frequency of each criterion in the resected regions and their combinations were assessed on FLAWS, according to the results of the assessment when the reviewers were aware of the location of the resected regions. Based on the findings of the 17 patients with an additional 3D-FLAIR scan when the reviewers were aware of the location of the resected regions, quantitative analysis of the regions of interest was used to compare the tissue contrast among 2D-axial FLAIR, 3D-FLAIR, and the FLAWS sequence. Visualization score analysis was used to evaluate the visualization of the five features on conventional, 3D-FLAIR, and FLAWS images. Finally, to explore the reason for false-positive results, a further evaluation of the whole brain FLAWS images was conducted for all the subjects.

Results

The sensitivity and specificity for detecting the FCD lesions on the FLAWS sequence were 71.9% and 71.1%, respectively. When the reviewers were blinded to the location of the resected regions, the detection rate of the FLAWS sequence was significantly higher than that of the conventional sequences (P = 0.00). In the 17 patients who underwent an additional 3D FLAIR scan, no statistically significant difference was found between the FLAWS and the 3D-FLAIR (P = 0.25). All the patients had at least two imaging features, one of which was “the blurred junction of the gray-white matter.” The transmantle sign, which is widely believed to be a specific feature of FCD type II, could also be observed in type I on the FLAWS sequence. The relative tissue contrast of FLAWS was higher than that of the 2D-FLAIR with respect to lesion/white matter (WM), deep gray matter (GM)/WM, and cortex/WM (P = 0.00 for all three measures) and higher than that of the 3D-FLAIR with respect to the lesion/WM (P = 0.01). The visualization score analysis showed that the visualization of FLAWS was more enhanced than that of the conventional and 3D-FLAIR images with respect to the blurred junction (P = 0.00 for both comparisons) and the abnormal signal intensity of the subcortical white matter (P = 0.01 for both comparisons). The thin-threadlike signal and individual FCD features outside the epileptogenic regions were considered the primary cause of the false-positive results of FLAWS.

Conclusions

FLAWS can help in the detection of FCD epileptogenic zones. It is recommended that epileptogenic zone on FLAWS be diagnosed based on a combination of two features, one of which should be the “blurred junction of the gray-white matter” in types I and II. In type III, the combination of “the blurred junction of the gray-white matter” with “abnormal signal intensity of subcortical white matter” is recommended.

•

FLAWS can help in the detection of FCD epileptogenic zones.

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Diagnosis of FCD lesions should be based on a combination of two features.

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The transmantle sign is not specific for FCD type II on FLAWS.

Pancreatic Duct in Autoimmune Pancreatitis: Intraindividual Comparison of Magnetic Resonance Pancreatography at 1.5 T and 3.0 T

OBJECTIVE

The aim of this study was to intraindividually compare magnetic resonance pancreatography (MRP) image quality at 1.5 T and 3.0 T when demonstrating main pancreatic duct (MPD) abnormalities in patients with autoimmune pancreatitis (AIP).

METHODS

Thirty prospectively enrolled patients with AIP underwent MRP at both 1.5 T and 3.0 T followed by endoscopic retrograde pancreatography before treatment. Two readers independently analyzed the MRP images and graded the visualization of MPD strictures and full-length MPD, using endoscopic retrograde pancreatography as the reference standard, as well as overall image artifacts on a 4-point scale. The contrast between the MPD and periductal area was calculated using a region-of-interest measurement.

RESULTS

Visualization scores of MPD strictures and full-length MPD, and summed scores of each qualitative analysis, were significantly greater at 3.0-T MRP than at 1.5-T MRP for both readers (P ≤ 0.02). There were less image artifacts at 3.0 T compared with 1.5 T (P ≤ 0.052). The contrast between the MPD and periductal area was significantly greater at 3.0-T MRP than at 1.5-T MRP (P < 0.001).

CONCLUSIONS

The MRP at 3.0 T was superior to 1.5-T MRP for demonstrating MPD abnormalities in AIP, with better image contrast and fewer image artifacts. Consequently, 3.0-T MRP may be useful for the diagnosis and management of patients with AIP.

Non-neoplastic diseases of the fallopian tube: MR imaging with emphasis on diffusion-weighted imaging

OBJECTIVE

We illustrate the magnetic resonance imaging (MRI) features of non-neoplastic tubaric conditions.

BACKGROUND

A variety of pathologic non-neoplastic conditions may affect the fallopian tubes. Knowledge of their imaging appearance is important for correct diagnosis. With recent advances in MRI, along with conventional MR sequences, diffusion-weighted imaging (DWI) sequences are available and may improve lesion characterization by discriminating the nature of the content of the dilated tube. Tubal fluid with low signal intensity on T1-weighted images, high signal intensity on T2-weighted images and no restricted diffusion on DWI is indicative of hydrosalpinx. Content with high signal intensity on T1-weighted images and restricted diffusion on DWI is suggestive of hematosalpinx associated with endometriosis or tubal pregnancy. A dilated tube with variable or heterogeneous signal intensity content on conventional MR sequences and restricted diffusion on DWI may suggest a pyosalpinx or tubo-ovarian abscess. We describe morphological characteristics, MR signal intensity features, enhancement behaviour and possible differential diagnosis of each lesion.

CONCLUSION

MRI is the method of choice to study adnexal pelvic masses. Qualitative and quantitative functional imaging with DWI can be of help in characterization of tubaric diseases, provided that findings are interpreted in conjunction with those obtained with conventional MRI sequences.

TEACHING POINTS

• Nondilated fallopian tubes are not usually seen on MR images. • MRI is the method of choice to characterize and localize utero-adnexal masses. • MRI allows characterization of lesions through evaluation of the fluid content's signal intensity. • DWI in conjunction with conventional MRI sequences may improve tissue characterization. • Pelvic inflammatory disease is the most common tubal pathology.

Application of ultrasonography in the assessment of skeletal muscles in children with and without neuromuscular disorders: a systematic review

The purpose of this study was to systematically review published studies (2000-2014) carried out on the application of ultrasonography (US) to evaluation of skeletal muscle size in children with and without neuromuscular disorders. Different databases including PubMed, Science Direct, OVID, MEDLINE, CINAHL, EMBASE, ProQuest and Google Scholar were searched. The key words used were: "children," "ultrasound," "skeletal muscles," "neuromuscular disease," "neurogenic disorders," "spina bifida," "myelomeningocele" and "reliability." Eighteen articles were found to be relevant. Eight studies applied US in combination with additional methods of assessment. Four of the 18 studies did not have a control group. Ten studies applied only US in the assessment of skeletal muscles in children with and without neuromuscular diseases. In 9 studies, there were children ranging widely in age, and in 3 studies US was used to determine normal values for skeletal muscles. According to the results of these 18 reviewed articles, US is an appropriate, reliable and highly predictive method for assessment of skeletal muscles in children.

High-dose dobutamine stress steady-state free precession (SSFP) cine MRI at 3T with patient adaptive local radiofrequency (RF) shimming using dual-source RF transmission

PURPOSE

To prospectively assess the feasibility, image quality, and diagnostic accuracy of high-dose dobutamine stress magnetic resonance imaging (DSMR) using steady-state free precession (SSFP) cine imaging at 3T applying a dual-source radiofrequency (RF) excitation magnetic resonance imaging (MRI) system with parallel transmission and patient adaptive local RF shimming.

MATERIALS AND METHODS

DSMR using SSFP cine imaging was performed in 44 patients at 3T scheduled for a clinically indicated coronary angiography. The effect of conventional versus dual-source RF transmission was assessed regarding homogeneity of the B1 field, contrast-to-noise ratios (CNRs) at rest, image quality, and diagnostic accuracy of DSMR using long and short axis.

RESULTS

The mean percentage of the intended flip angle within the heart increased from 88 ± 9.1% with single-source to 103 ± 5.6% (P < 0.001) dual-source RF transmission. CNR increased for dual-source particularly at the apex (63.4 ± 24.2 vs. 36.5 ± 16.5, P < 0.001) but also at the base of the left ventricle (LV) (50.1 ± 14.8 vs. 39.3 ± 15.8, P < 0.001). Image quality of dual-source was higher both at rest (2.8 ± 0.5 vs. 2.6 ± 0.7, P < 0.001) and stress (2.5 ± 0.7 vs. 2.0 ± 1.0, P < 0.001). The number of segments with severe artifacts or nondiagnostic image quality at stress was lower with dual-source RF transmission (8% vs. 27%, P < 0.001). The diagnostic accuracy of DSMR in coronary territories using dual-source RF transmission was significantly higher (77% vs. 65%, P = 0.04).

CONCLUSION

Patient adaptive local RF shimming using dual-source RF transmission provided significantly improved image quality and higher diagnostic accuracy of SSFP during DSMR at 3T compared to conventional RF transmission.

3 T MRI uterine peristalsis: comparison of symptomatic fibroid patients versus controls

AIM

To compare uterine peristalsis between symptomatic fibroid patients and normal subjects and to determine the possible effect of fibroid characteristics on uterine peristalsis at high-field magnetic resonance imaging (MRI).

MATERIALS AND METHODS

The present study included 20 symptomatic fibroid patients (age range 39-53 years) and 20 normal subjects (age range 19-46 years). MRI images were obtained during the peri-ovulatory phase using 3 T MRI using a sagittal T2 turbo spin-echo sequence and a half-Fourier acquisition single-shot turbo spin-echo sequence for display on cine mode. Two radiologists independently evaluated the images for the presence of uterine peristalsis by confidence level. In cases where peristalsis was present, the images were also evaluated for peristalsis frequency and direction. For fibroid patients, uterine and index fibroid volume, fibroid burden and index fibroid location were also recorded.

RESULTS

Uterine peristalsis was significantly decreased in symptomatic fibroid patients compared with normal controls (p < 0.01). Peristalsis frequency in fibroid patients was also lower than in normal subjects. Direction of peristalsis was cervix-to-fundus for the majority of fibroid patients and controls. There was no significant relationship between fibroid characteristics, such as uterine volume, index fibroid volume, index fibroid location, and fibroid number in fibroid patients with, and fibroid patients without peristalsis.

CONCLUSION

In women with symptomatic fibroids, the presence of uterine peristalsis is significantly decreased compared to normal controls on 3 T cine MRI. The presence of fibroids appears to disturb the normal conduction of uterine peristalsis and may interfere with fluid (e.g., menses, sperm) transport.

Three-dimensional T2-weighted imaging for liver MRI: clinical values of tissue-specific variable refocusing flip-angle turbo spin echo imaging

PURPOSE

To assess the clinical utility of tissue-specific variable refocusing flip-angle (VRFA) turbo-spin echo imaging for three-dimensional T2-weighted imaging (3D-T2WI) of the liver.

MATERIALS AND METHODS

Fifty-nine patients were scanned with three types of fat-suppressed T2WI for the comparison: two-dimensional single-shot turbo spin echo T2WI (ssT2WI), 3D-T2WI with tissue-specific VRFA (VISTA-TSV), and 3D-T2WI with low-constant VRFA (VISTA). Qualitatively, artifacts in the left and right lobes of the liver and black-blood effects in the liver were compared using the Wilcoxon signed-rank test with the Bonferroni correction. The detection and correct characterization rates of liver lesions were compared using McNemar's test.

RESULTS

VISTA-TSV showed reduced artifacts in the left and right lobes of the liver compared with VISTA (P < 0.017). The artifacts shown by VISTA-TSV were equivalent to those shown by ssT2WI. The black-blood effects of VISTA-TSV and VISTA were better than that of ssT2WI (P < 0.017). VISTA-TSV showed the best detection and correct characterization rate of liver lesions among the three imaging techniques (P < 0.05).

CONCLUSION

3D-T2WI with tissue-specific VRFA can reduce artifacts of the liver, sufficiently suppress the signal in blood vessels, and has a potential to improve the detection and correct characterization rates of liver lesions.

Advanced MRI in malignant neoplasms of the uterus

Conventional magnetic resonance imaging (MRI) such as T1-weighted and T2-weighted images of the female pelvis provide morphological information with excellent tissue contrast, which reflects the pathology of malignant diseases of the uterus. Owing to the recent improvement in hardware and software, in combination with extensive research in imaging techniques, not only MRI at higher magnetic field was facilitated, but also insight into tumor pathophysiology was provided. These methods include diffusion-weighted imaging (DWI), dynamic contrast-enhanced MRI (DCE-MRI) with pharmacokinetic analysis, and MR spectroscopy (MRS). The application of these techniques is expanding from the brain to the body because information on the tissue microenvironment and cytoarchitecture is helpful for lesion characterization, evaluation of treatment response after chemotherapy or radiation, differentiating posttherapeutic changes from residual active tumor, and for detecting recurrent cancer. These techniques may provide clues to optimize the treatment of patients with malignant diseases of the uterus. In the first half of this article we provide an overview of the technical aspects of MRI of the female pelvis, especially focusing on the state-of-the-art techniques such as 3 T MRI, DCE-MRI, DWI, etc. For the latter half we review the clinical aspects of these newly developed techniques, focusing on how these techniques are applicable, what has been revealed with respect to clinical impact, and the remaining problems.

Clinical application of magnetic resonance imaging in management of breast cancer patients receiving neoadjuvant chemotherapy

Neoadjuvant chemotherapy (NAC), also termed primary, induction, or preoperative chemotherapy, is traditionally used to downstage inoperable breast cancer. In recent years it has been increasingly used for patients who have operable cancers in order to facilitate breast-conserving surgery, achieve better cosmetic outcome, and improve prognosis by reaching pathologic complete response (pCR). Many studies have demonstrated that magnetic resonance imaging (MRI) can assess residual tumor size after NAC, and that provides critical information for planning of the optimal surgery. NAC also allows for timely adjustment of administered drugs based on response, so ineffective regimens could be terminated early to spare patients from unnecessary toxicity while allowing other effective regimens to work sooner. This review article summarizes the clinical application of MRI during NAC. The use of different MR imaging methods, including dynamic contrast-enhanced MRI, proton MR spectroscopy, and diffusion-weighted MRI, to monitor and evaluate the NAC response, as well as how changes of parameters measured at an early time after initiation of a drug regimen can predict final treatment outcome, are reviewed. MRI has been proven a valuable tool and will continue to provide important information facilitating individualized image-guided treatment and personalized management for breast cancer patients undergoing NAC.

Seven-Tesla MRI of the female pelvis

OBJECTIVES

The aim of this study was to investigate the feasibility of 7-T contrast-enhanced MR imaging of the female pelvis.

METHODS

Ten healthy female volunteers were examined on a 7-T whole-body MR system utilising a custom-built eight-channel transmit/receive radiofrequency body coil. The examination protocol included (1) T1-weighted fat-saturated 2D spoiled gradient echo (FLASH), (2) dynamic T1-weighted fat-saturated 3D FLASH, and (3) T2-weighted TSE sequences. For qualitative image analysis pelvic anatomy, uterine zonal anatomy and image impairment due to artefacts was assessed using a five-point scale. For quantitative analysis contrast ratios between the junctional zone and myometrium were obtained for T2-weighted MRI.

RESULTS

Two-dimensional FLASH MRI offered the best overall image quality (meancontrast-enhanced 4.9) and highest tissue contrast (meancontrast-enhanced 4.7). T2-weighted TSE imaging provided a moderate to high conspicuity of the uterine zonal anatomy with mean scores ranging from 3.5 for endometrium to 4.65 for myometrium. Overall image impairment was rated strongest for T2-weighted MRI (2.9) and least for 2D FLASH MRI (mean 4.2).

CONCLUSION

This study demonstrated the feasibility of 7-T T1-weighted MRI of the female pelvis and current constraints associated with T2-weighted MRI.

KEY POINTS

• Dynamic contrast-enhanced female pelvis MR imaging at 7 T is feasible. • Unenhanced T1-weighted MRI offers inherent hyperintense delineation of pelvic arterial vasculature. • Two-dimensional FLASH MRI provided best overall image quality and least artefact impairment.

Ultrahigh-field magnetic resonance imaging: the clinical potential for anatomy, pathogenesis, diagnosis and treatment planning in neck and spine disease

An increase of the magnetic field strength to ultrahigh-field yields advantageous as well as disadvantageous changes in physical effects. The beneficial increase in signal/noise ratio can be leveraged into higher spatiotemporal resolution, and an exacerbation of artifacts can impede ultrahigh-field imaging. With the successful introduction of intracranial and musculoskeletal imaging at 7 T, recent advances in coil design have created opportunities for further applications of ultrahigh-field magnetic resonance (MR) imaging in other parts of the body. Initial studies in 7 T neck and spine MR imaging have revealed promising insights and new challenges, demanding further research and methodological optimization.

Breast cancer: evaluation of response to neoadjuvant chemotherapy with 3.0-T MR imaging

PURPOSE

To assess how the molecular biomarker status of a breast cancer, including human epidermal growth factor receptor 2 (HER2), hormone receptors, and the proliferation marker Ki-67 status, affects the diagnosis at 3.0-T magnetic resonance (MR) imaging.

MATERIALS AND METHODS

This study was approved by the institutional review board and was HIPAA compliant. Fifty patients (age range, 28-82 years; mean age, 49 years) receiving neoadjuvant chemotherapy were monitored with 3.0-T MR imaging. The longest dimension of the residual cancer was measured at MR imaging and correlated with pathologic findings. Patients were further divided into subgroups on the basis of HER2, hormone receptor, and Ki-67 status. Pathologic complete response (pCR) was defined as when there were no residual invasive cancer cells. The Pearson correlation was used to correlate MR imaging-determined and pathologic tumor size, and the unpaired t test was used to compare MR imaging-pathologic size discrepancies.

RESULTS

Of the 50 women, 14 achieved pCR. There were seven false-negative diagnoses at MR imaging. The overall sensitivity, specificity, and accuracy for diagnosing invasive residual disease at MR imaging were 81%, 93%, and 84%, respectively. The mean MR imaging-pathologic size discrepancy was 0.5 cm ± 0.9 (standard deviation) for HER2-positive cancer and 2.3 cm ± 3.5 for HER2-negative cancer (P = .009). In the HER2-negative group, the size discrepancy was smaller for hormone receptor-negative than for hormone receptor-positive cancers (1.0 cm ± 1.1 vs 3.0 cm ± 4.0, P = .04). The size discrepancy was smaller in patients with 40% or greater Ki-67 expression (0.8 cm ± 1.1) than in patients with 10% or less Ki-67 expression (3.9 cm ± 5.1, P = .06).

CONCLUSION

The diagnostic accuracy of breast MR imaging is better in more aggressive than in less aggressive cancers. When MR imaging is used for surgical planning, caution should be taken with HER2-negative hormone receptor-positive cancers.

Dual-source parallel radiofrequency excitation body MR imaging compared with standard MR imaging at 3.0 T: initial clinical experience

PURPOSE

To prospectively compare the image quality and homogeneity of magnetic resonance (MR) images obtained by using a dual-source parallel radiofrequency (RF) excitation body MR imaging system with parallel transmission and independent RF shimming with the image quality and homogeneity of single-source MR images obtained by using standard sequences for routine clinical use in patients at 3.0 T.

MATERIALS AND METHODS

After institutional review board approval and informed patient consent were obtained, a dual-source parallel RF excitation 3.0-T MR system with independent RF shimming and parallel transmission technology was used to examine 28 patients and was compared with a standard 3.0-T MR system with single RF transmission. The RF power was distributed to the independent ports of the system body coil by using two RF transmission sources with full software control, enabling independent control of the phase and amplitude of the RF waveforms. Axial T2-weighted fast spin-echo (SE) and diffusion-weighted (DW) liver images, axial T2-weighted fast SE pelvic images, and sagittal T1- and T2-weighted fast SE spinal images were obtained by using dual- and single-source RF excitation. Two radiologists independently evaluated the images for homogeneity and image quality. Statistical significance was calculated by using the nonparametric Wilcoxon signed rank test. Interobserver agreement was determined by using Cohen kappa and Kendall tau-b tests.

RESULTS

Image quality comparisons revealed significantly better results with dual-source rather than single-source RF excitation at T2-weighted liver MR imaging (P = .001, kappa = 1.00) and better results at DW liver imaging at a statistical trend level (P = .066, tau-b > 0.7). Owing to reduced local energy deposition, fewer acquisitions and shorter repetition times could be implemented with dual-source RF excitation pelvic and spinal MR imaging, with image acquisition accelerating by 18%, 33%, and 50% compared with the acquisitions with single-source RF excitation. Image quality did not differ significantly between the two MR techniques (P > .05, tau-b > 0.5).

CONCLUSION

Dual-source parallel RF excitation body MR imaging enables reduced dielectric shading, improved homogeneity of the RF magnetic induction field, and accelerated imaging at 3.0 T.

MR imaging of endometrial carcinoma for preoperative staging at 3.0 T: comparison with imaging at 1.5 T

PURPOSE

To prospectively compare magnetic resonance imaging (MRI) at 3.0 T and 1.5 T in the same patients for preoperative evaluation of endometrial carcinoma.

MATERIALS AND METHODS

Thirty consecutive patients with endometrial carcinoma underwent MRI at both 3.0 T and 1.5 T as well as surgery. Quantitative and qualitative analyses were performed. Two radiologists independently evaluated images. MR findings were compared with surgicopathologic findings.

RESULTS

Image homogeneity of T2-weighted images at 3.0 T was significantly inferior to that at 1.5 T (P = 0.007). The scores of image homogeneity and susceptibility artifacts were not significantly different between 3.0 T gadolinium-enhanced imaging and 1.5 T imaging (P = 0.09 and 0.36). Kappa statistics showed good interobserver agreement between the two radiologists for local-regional staging on T2-weighted images (kappa>0.6). The area under the receiver operating characteristic curve (Az) values for T2-weighted imaging in terms of myometrial invasion, cervical invasion, and lymph node metastases were 0.88 (3.0 T) versus 0.91 (1.5 T), 0.84 versus 0.83, and 0.94 versus 0.95 for reader 1, respectively. There were no significant differences between imaging at 3.0 T and at 1.5 T in Az values for either reader (P > 0.35).

CONCLUSION

3.0 T MRI is an equivalent imaging modality to 1.5 T imaging for presurgical evaluation of endometrial carcinoma, although not significantly superior to 1.5 T imaging.

[Pelvic MRI at 3.0 Tesla]

High resolution MR imaging is ideal for pelvic imaging. To achieve good image quality at 3.0 Tesla MR, one may not simply import protocols used at 1.5 Tesla MR. Issues specific to 3.0 Tesla MR imaging must be considered including chemical shift, magnetic susceptibility, dielectric effect, specific absorption rates (SAR), motion artifacts and optimal echo time (TE) and repetition tome (TR) to achieve the desired tissue contrast. High quality pelvic MRI (prostate, rectum, and female pelvis) at 3.0 Tesla is possible. In addition, it offers potential advantages due to its ability to provide excellent vascular imaging and advances with functional imaging (diffusion, spectroscopy). This article discusses the parameters required to achieve quality pelvic imaging at 3.0 Tesla, the specifics of high-field MR imaging, and illustrates achievable clinical results.

Uterine cervical carcinoma: preoperative staging with 3.0-T MR imaging--comparison with 1.5-T MR imaging

PURPOSE

To prospectively evaluate the efficacy of 3.0-T magnetic resonance (MR) imaging in the preoperative staging of cervical carcinoma compared with that at 1.5-T imaging, with surgery and pathologic analysis as the reference standards.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Thirty-one consecutive patients (age range, 27-71 years; mean age, 51.1 years) underwent 3.0- and 1.5-T MR imaging. Quantitative and qualitative analyses were performed. Two radiologists independently evaluated images in terms of local-regional staging. MR findings were compared with surgicopathologic findings.

RESULTS

Mean tumor signal-to-noise ratios, mean cervical stroma signal-to-noise ratios, and mean tumor-to-cervical stroma contrast-to-noise ratios at 3.0-T imaging were significantly higher than those at 1.5-T imaging (P = 9.1 x 10(-6), P = 1.8 x 10(-6), and P = .008, respectively). Image homogeneity at 3.0-T imaging was significantly inferior to that at 1.5-T imaging (P = .005). There were no significant differences in terms of the degree of susceptibility artifacts. Interobserver agreement between the two radiologists for local-regional staging was good or excellent (kappa = 0.65-0.89). Sensitivity, specificity, and area under the receiver operating characteristic curve for radiologist 1 in the evaluation of parametrial invasion were (a) 75% for both 3.0- and 1.5-T imaging, (b) 70% for both 3.0- and 1.5-T imaging, and (c) 0.82 for 3.0-T imaging and 0.85 for 1.5-T imaging, respectively. Corresponding values for vaginal invasion were (a) 67% for both 3.0- and 1.5-T imaging, (b) 68% for 3.0-T imaging and 72% for 1.5-T imaging, and (c) 0.62 for 3.0-T imaging and 0.67 for 1.5-T imaging, respectively. Corresponding values for lymph node metastases were (a) 57% for both 3.0- and 1.5-T imaging, (b) 83% for 3.0-T imaging and 88% for 1.5-T imaging, and (c) 0.72 for 3.0-T imaging and 0.78 for 1.5-T imaging, respectively. Neither radiologist noted significant differences between values obtained with 3.0-T imaging and those obtained with 1.5-T imaging (P > .5 for all comparison pairs).

CONCLUSION

In this study, 3.0-T MR imaging was characterized by high diagnostic accuracy in the presurgical evaluation of patients with cervical carcinoma, although 3.0-T imaging was not significantly superior to 1.5-T imaging.

MR imaging of prostate cancer at 3T with an external phased-array coil: evaluation of T2-weighted images

1.5T Magnetic resonance (MR) imaging has become an accepted method for assessing prostate cancer. However, the role of 1.5T MRI in local staging of prostate cancer is limited. It is hoped that 3.0T MRI will be more useful in local staging of prostate cancer. The purpose of this study was to evaluate the tissue contrast, artifact presence, and image quality of T2-weighted images (T2WI) of prostate cancer using 3T MRI with a phased-array coil at different slice thicknesses and fields of view (FOV). We examined 15 patients with prostate cancer. We obtained MR images at slice thicknesses of 2 mm and 5 mm in both small and large FOV. The image obtained at a slice thickness of 2 mm with a small FOV had inferior tissue contrast compared to the other images (P<0.05), but there was no statistically significant difference in contrast between images obtained at a slice thickness of 2 mm with a large FOV and those obtained at a slice thickness of 5 mm. Artifacts were rated equally among the parameter combinations. The overall image quality obtained at a slice thickness of 2 mm with a large FOV was significantly superior to the other three imaging parameters (p<0.05). The image obtained at a slice thickness of 2 mm with a large FOV was superior to the other three images in evaluating T2WI of prostate cancer with 3T MRI.

Reference data for in vivo magnetic resonance imaging properties of meniscoids in the cervical zygapophyseal joints

STUDY DESIGN

Prospective in vivo study of meniscoids in the cervical zygapophyseal joints.

OBJECTIVE

To generate reference data for in vivo magnetic resonance (MR) imaging properties of meniscoids in the cervical zygapophyseal joints.

SUMMARY OF BACKGROUND DATA

Meniscoids, also called synovial folds, are tiny anatomic structures within the zygapophyseal joints. It has been suggested that pathologic conditions of meniscoids may be a potential source of cervical pain. Prior studies were limited to in vitro observations. To identify pathologic conditions of the meniscoids, it is necessary to obtain reference data of basic in vivo MR imaging properties of meniscoids in a healthy population.

METHODS

Fifty-six healthy volunteers (33 women, 23 men; mean age 42.0 +/- 17.1 years) were investigated in a 3.0 Tesla MR scanner using high resolution isotropic 3-dimensional sequences. Presence, size, location, and signal intensity of the meniscoids were assessed, and their dependence on sex, age, body mass index, and degenerative changes were analyzed by t test and correlation analysis.

RESULTS

There was no significant difference in presence (20.3 +/- 4.8 vs. 19.7 +/- 4.8) and size (3.8 +/- 0.7 mm vs. 4.1 +/- 0.5 mm) of meniscoids between women and men. Presence of meniscoids decreased with increasing age (r = -0.38, P = 0.004). Size of meniscoids did not significantly depend on age (r = 0.02, P = 0.91). Meniscoid entrapment (location) was a rare condition (0.4%). Tissue composition (signal intensities) of the meniscoids was 61.6% mainly fatty, 15.8% mainly fibrous, and 22.6% mixed.

CONCLUSION

Basic data about in vivo MR imaging properties of cervical meniscoids in a healthy population have been successfully generated. Subsequent studies may use these data as reference for the identification of meniscoid pathologies.

Muscle ultrasound in neuromuscular disorders

Muscle ultrasound is a useful tool in the diagnosis of neuromuscular disorders, as these disorders result in muscle atrophy and intramuscular fibrosis and fatty infiltration, which can be visualized with ultrasound. Several prospective studies have reported high sensitivities and specificities in the detection of neuromuscular disorders. Although not investigated in large series of patients, different neuromuscular disorders tend to show specific changes on muscle ultrasound, which can be helpful in differential diagnosis. For example, Duchenne muscular dystrophy results in a severe, homogeneous increase of muscle echo intensity with normal muscle thickness, whereas spinal muscular atrophy shows an inhomogeneous increase of echo intensity with severe atrophy. A major advantage of muscle ultrasound, compared to other imaging techniques, is its ability to visualize muscle movements, such as muscle contractions and fasciculations. This study reviews the possibilities and limitations of ultrasound in muscle imaging and its value as a diagnostic tool in neuromuscular disorders.

A review of MR physics: 3T versus 1.5T

This article illustrates changes in the underlying physics concepts related to increasing the main magnetic field from 1.5T to 3T. The effects of these changes on tissue constants and practical hardware limitations is discussed as they affect scan time, quality, and contrast. Changes in susceptibility artifacts, chemical shift artifacts, and dielectric effects as a result of the increased field strength are also illustrated. Based on these fundamental considerations, an overall understanding of the benefits and constraints of signal-to-noise ratio and contrast-to-noise ratio changes between 1.5T and 3T MR systems is developed.

Clinical advantages of 3.0 T MRI over 1.5 T

Since approval by the FDA in 2000, human MR imaging (MRI) at 3.0 T has been increasingly used in clinical practice. In spite of the potential technical challenges, a number of clinical advantages of 3.0 T MRI over 1.5 T have been identified in the recent years. This article reviews the benefits and the current knowledge of 3.0 T whole-body MRI from an evidence-based perspective and summarizes its clinical applications.

Body and Cardiovascular MR Imaging at 3.0 T

Potential advantages of magnetic resonance (MR) imaging at 3 T include higher signal-to-noise ratios, better image contrast, particularly in gadolinium-enhanced applications, and better spectral separation for spectroscopic applications. In terms of clinical imaging, these advantages can mean higher-spatial-resolution images, faster imaging, and improved MR spectroscopy. However, achieving superior imaging and spectroscopic quality at 3 T can be challenging. This review discusses many of the problems encountered in body and cardiovascular MR imaging at 3 T, such as increased susceptibility, B1 field inhomogeneity, and increased specific absorption rate. The article also considers solutions that are being pursued, such as parallel imaging, variable-rate selective excitation, and variable flip angle sequences. A review of the most commonly used pulse sequences provides practical tips on how these can be optimized for 3-T imaging. In the coming few years, substantial improvements in 3-T technology for clinical imaging and spectroscopy will undoubtedly be seen. An understanding of the basic principles on which these developments are based will help radiologists translate the advances into better imaging studies and, ultimately, better patient care.

MR Imaging of Gynecologic Diseases at 3T

MR imaging using anatomic, chemical, and functional information offers huge potential for the management of the gynecologic patient. By differentiating benign from malignant disease with very high specificity, it can aid the selection of patients requiring further treatment and determine the level of urgency. Staging accuracy, which equals that obtained at laparotomy, allows appropriate clinical expertise to be organized before surgery or the deferment of surgery until later in the treatment pathway and is a cost-effective use of resources. This article compares and contrasts MR imaging of gynecologic conditions at 1.5 and 3T and defines a role for high field imaging for these clinical conditions.

Detection of brain metastasis at 3T: comparison among SE, IR-FSE and 3D-GRE sequences

The objective of this study is to compare the detectability of brain metastases at 3T among three contrast-enhanced sequences, spin-echo (SE) sequence, inversion recovery fast SE (IR-FSE) sequence (both with section thickness of 6 mm), and three-dimensional fast spoiled gradient-echo (3D fast SPGR) sequence with 1.4 mm isotropic voxel. First, phantom studies were performed to quantify the contrast-enhancement ratio (CER) with three sequences. In 21 consecutive patients with brain metastases, axial images of three sequences at 3T were obtained after administration of gadoteridol. Two neuroradiologists assessed the detectability of brain metastases for the three sequences. In the phantom study, no evident difference in the CER was demonstrated among three sequences. Significantly more brain metastases were detected with 3D fast SPGR than with SE and IR-FSE (a total of 97 lesions with 3D fast SPGR vs. 64 with SE and 63 with IR-FSE). In particular, 3D fast SPGR was superior to the other two sequences in detection of the small lesions (<3 mm). At 3T, the contrast-enhanced 3D fast SPGR with 1.4 mm isotropic voxel is clinically more valuable for detecting small brain metastases than the SE and IR-FSE with section thickness of 6 mm.

High-field magnetic resonance imaging of meniscoids in the zygapophyseal joints of the human cervical spine

STUDY DESIGN

Prospective in vitro study of meniscoids in the cervical zygapophysial joints. OBJECTIVES.: To assess the use of high-field magnetic resonance imaging (MRI) as a potential tool for evaluating meniscoids of the cervical zygapophysial joints.

SUMMARY OF BACKGROUND DATA

Pain originating from the cervical spine is a frequent condition. It has been suggested that pathologic conditions of meniscoids within the zygapophysial joints may cause pain.

METHODS

Six zygapophysial joints from one embalmed human body were investigated with a 3.0-T MR unit, equipped with a microimaging-set. MRIs were correlated with microanatomical sections.

RESULTS

High-quality images of the meniscoids were obtained for all joints examined. There was a good correlation between the anatomic features derived from MRI and the microanatomical sections.

CONCLUSIONS

High-field MRI was successfully implemented as a noninvasive method for imaging the meniscoids in cervical zygapophysial joints. The results of this in vitro study indicate that high-field MRI may be feasible in evaluating patients with cervical pain possibly related to meniscoid pathology.

Intra-individual comparison of image contrast in SPIO-enhanced liver MRI at 1.5T and 3.0T

The purpose of the study was to examine if the higher susceptibility at 3.0 Tesla (T) compared to 1.5 T will affect the contrast in MR imaging of the liver after application of superparamagnetic iron oxide particles (SPIO). The study was approved by our institutional review board and informed consent was obtained. Seventeen healthy volunteers were examined in a prospective, intra-individual comparative study within one day on a 1.5 T and a 3.0 T MRI system. T2 weighted TSE sequences were acquired after bolus injection of a SPIO contrast agent. Image contrast and signal to noise ratio (SNR) were compared between the field strengths. Image contrast was calculated between the liver tissue and the kidneys / spleen / muscles and fluids. The students'T-test was used for statistical analysis. No influence of the higher field strength could be observed on image contrast except for the liver / muscle contrast. This was due to a distinct SNR increase of the muscle tissue at 3.0 T as a result of their relaxation properties. The higher susceptibility at 3.0 T compared to 1.5 T does not translate into a stronger signal attenuation of the SPIO enhanced liver parenchyma.

Imaging the female pelvis at 3.0 T

Three-Tesla whole body imaging is rapidly becoming part of routine clinical practice. Although it is generally thought that pelvic imaging at 3.0 T will be beneficial because of increased signal to noise and greater spectral separation, adjustments in protocol and sequence parameters are necessary to optimize image quality. The question remains as to whether 3.0-T imaging will offer further benefits beyond 1.5 T in terms of lesion characterization and functional imaging. This article aims to address safety concerns and to illustrate the potential benefits and technical challenges of imaging the female pelvis at 3.0 T. Imaging protocols and sequence parameters for routine gynecologic indications are suggested, and potential clinical applications at 3.0 T are discussed such as magnetic resonance spectroscopy, perfusion, diffusion weighted imaging, and the use of alternate contrast agents.

Muskuloskeletal MR imaging at 3.0 T: current status and future perspectives

Magnetic resonance (MR) imaging has become an important diagnostic tool in evaluation of the musculoskeletal system. While most examinations are currently performed at magnetic field strengths of 1.5 T or lower, whole-body MR systems operating at 3.0 T have recently become available for clinical use. The higher field strengths promise various benefits, including increased signal-to-noise ratios, enhanced T2* contrast, increased chemical shift resolution, and most likely a better diagnostic performance in various applications. However, the changed T1, T2, and T2* relaxation times, the increased resonance-frequency differences caused by susceptibility and chemical-shift differences, and the increased absorption of radiofrequency (RF) energy by the tissues pose new challenges and/or offer new opportunities for imaging at 3.0 T compared to 1.5 T. Some of these issues have been successfully addressed only in the very recent past. This review discusses technical aspects of 3.0 T imaging as far as they have an impact on clinical routine. An overview of the current data is presented, with a focus on areas where 3.0 T promises equivalent or improved performance compared 1.5 T or lower field strengths.