1.5 vs 3 Tesla Magnetic Resonance Imaging: A Review of Favorite Clinical Applications for Both Field Strengths-Part 1

ABSTRACT

Whole-body magnetic resonance imaging (MRI) systems with a field strength of 3 T have been offered by all leading manufacturers for approximately 2 decades and are increasingly used in clinical diagnostics despite higher costs. Technologically, MRI systems operating at 3 T have reached a high standard in recent years, as well as the 1.5-T devices that have been in use for a longer time. For modern MRI systems with 3 T, more complexity is required, especially for the magnet and the radiofrequency (RF) system (with multichannel transmission). Many clinical applications benefit greatly from the higher field strength due to the higher signal yield (eg, imaging of the brain or extremities), but there are also applications where the disadvantages of 3 T might outweigh the advantages (eg, lung imaging or examinations in the presence of implants). This review describes some technical features of modern 1.5-T and 3-T whole-body MRI systems, and reports on the experience of using both types of devices in different clinical settings, with all sections written by specialist radiologists in the respective fields.This first part of the review includes an overview of the general physicotechnical aspects of both field strengths and elaborates the special conditions of diffusion imaging. Many relevant aspects in the application areas of musculoskeletal imaging, abdominal imaging, and prostate diagnostics are discussed.

Non-enhanced versus low-dose contrast-enhanced renal magnetic resonance angiography at 7 T: a feasibility study

Background Considering the currently reported association between a repetitive application and cumulative dosage of Gadolinium (Gd)-based contrast agents and Gd-deposition in brain tissue as well as the risk for the advent of nephrogenic systemic fibrosis (NSF), techniques allowing for a dose reduction become an important key aspect aside from non-enhanced magnetic resonance angiography (MRA) techniques. Thus, this study was focused on the reduction and/or complete omission of contrast agent for renal MRA at 7T. Purpose To evaluate the performance of time-of-flight MRA versus low-dose contrast-enhanced (CE) renal MRA at 7T. Material and Methods Ten healthy volunteers were examined on a 7T MR system comprising a TOF MRA and three-dimensional (3D) fast low angle shot spoiled gradient-echo sequence (FLASH) MRA after administration of one-quarter of clinical dose of gadobutrol. Qualitative image analysis was performed including overall image quality, artery delineation and presence of artifacts. Contrast ratio (CR), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of the renal arteries were calculated. Results TOF MRA and low-CE MRA achieved comparable overall ratings, with slightly superior delineation of the main renal arteries in TOF MRA (TOF = 3.10 ± 0.75, low-CE = 2.95 ± 0.75). Segmental branches outside and inside the parenchyma were delineated significantly better on TOF MRA. Quantitative analysis demonstrated the superiority of TOF MRA, yielding higher scores for CR, SNR, and CNR. Conclusion The initial results of our study demonstrate the feasibility and comparable diagnostic performance of TOF and low-dose CE renal MRA at 7T.

1.5 versus 3 versus 7 Tesla in abdominal MRI: A comparative study

Objectives

The aim of this study was to investigate and compare the feasibility as well as potential impact of altered magnetic field properties on image quality and potential artifacts of 1.5 Tesla, 3 Tesla and 7 Tesla non-enhanced abdominal MRI.

Materials and methods

Magnetic Resonance (MR) imaging of the upper abdomen was performed in 10 healthy volunteers on a 1.5 Tesla, a 3 Tesla and a 7 Tesla MR system. The study protocol comprised a (1) T1-weighted fat-saturated spoiled gradient-echo sequence (2D FLASH), (2) T1-weighted fat-saturated volumetric interpolated breath hold examination sequence (3D VIBE), (3) T1-weighted 2D in and opposed phase sequence, (4) True fast imaging with steady-state precession sequence (TrueFISP) and (5) T2-weighted turbo spin-echo (TSE) sequence. For comparison reasons field of view and acquisition times were kept comparable for each correlating sequence at all three field strengths, while trying to achieve the highest possible spatial resolution. Qualitative and quantitative analyses were tested for significant differences.

Results

While 1.5 and 3 Tesla MRI revealed comparable results in all assessed features and sequences, 7 Tesla MRI yielded considerable differences in T1 and T2 weighted imaging. Benefits of 7 Tesla MRI encompassed an increased higher spatial resolution and a non-enhanced hyperintense vessel signal at 7 Tesla, potentially offering a more accurate diagnosis of abdominal parenchymatous and vasculature disease. 7 Tesla MRI was also shown to be more impaired by artifacts, including residual B₁ inhomogeneities, susceptibility and chemical shift artifacts, resulting in reduced overall image quality and overall image impairment ratings. While 1.5 and 3 Tesla T2w imaging showed equivalently high image quality, 7 Tesla revealed strong impairments in its diagnostic value.

Conclusions

Our results demonstrate the feasibility and overall comparable imaging ability of T1-weighted 7 Tesla abdominal MRI towards 3 Tesla and 1.5 Tesla MRI, yielding a promising diagnostic potential for non-enhanced Magnetic Resonance Angiography (MRA). 1.5 Tesla and 3 Tesla offer comparably high-quality T2w imaging, showing superior diagnostic quality over 7 Tesla MRI.

Post-mortem whole-body magnetic resonance imaging of human fetuses: a comparison of 3-T vs. 1.5-T MR imaging with classical autopsy

OBJECTIVE

To prospectively compare diagnostic accuracy of fetal post-mortem whole-body MRI at 3-T vs. 1.5-T.

METHODS

Between 2012 and 2015, post-mortem MRI at 1.5-T and 3-T was performed in fetuses after miscarriage/stillbirth or termination. Clinical MRI diagnoses were assessed using a confidence diagnostic score and compared with classical autopsy to derive a diagnostic error score. The relation of diagnostic error for each organ group with gestational age was calculated and 1.5-T with 3-T was compared with accuracy analysis.

RESULTS

135 fetuses at 12-41 weeks underwent post-mortem MRI (followed by conventional autopsy in 92 fetuses). For all organ groups except the brain, and for both modalities, the diagnostic error decreased with gestation (P < 0.0001). 3-T MRI diagnostic error was significantly lower than that of 1.5-T for all anatomic structures and organ groups, except the orbits and brain. This difference was maintained for fetuses <20 weeks gestation. Moreover, 3-T was associated with fewer non-diagnostic scans and greater concordance with classical autopsy than 1.5-T MRI, especially for the thorax, heart and abdomen in fetuses <20 weeks.

CONCLUSION

Post-mortem fetal 3-T MRI improves confidence scores and overall accuracy compared with 1.5-T, mainly for the thorax, heart and abdomen of fetuses <20 weeks of gestation.

KEY POINTS

• In PM-MRI, diagnostic error using 3-T is lower than that with 1.5-T. • In PM-MRI, diagnostic scan rate is higher using 3-T than 1.5-T. • In PM-MRI, concordance with classical autopsy increases with 3-T. • PM-MRI using 3-T is particularly interesting for thoracic and abdominal organs. • PM-MRI using 3-T is particularly interesting for fetuses < 20 weeks' gestation.

Cardiovascular MR imaging at 3 T: opportunities, challenges, and solutions

Although 3-T magnetic resonance (MR) imaging is well established in neuroradiology and musculoskeletal imaging, it is in the nascent stages in cardiovascular imaging applications, and there is limited literature on this topic. The primary advantage of 3 T over 1.5 T is a higher signal-to-noise ratio (SNR), which can be used as such or traded off to improve spatial or temporal resolution and decrease acquisition time. However, the actual gain in SNR is limited by other factors and modifications in sequences adapted for use at 3 T. Higher resonance frequencies result in improved spectral resolution, which is beneficial for fat suppression and spectroscopy. The higher T1 values of tissues at 3 T aid in myocardial tagging, angiography, and perfusion and delayed-enhancement sequences. However, there are substantial challenges with 3-T cardiac MR imaging, including higher magnetic field and radiofrequency inhomogeneities and susceptibility effects, which diminish image quality. Off-resonance artifacts are particularly challenging, especially with steady-state free precession sequences. These artifacts can be managed by using higher-order shimming, frequency scouts, or low repetition times. B1 inhomogeneities can be managed by using radiofrequency shimming, multitransmit coils, or adiabatic pulses. Chemical shifts are also increased at 3 T. The higher radiofrequency results in higher radiofrequency deposition power and a higher specific absorption rate. MR angiography, dynamic first-pass perfusion sequences, myocardial tagging, and MR spectroscopy are more effective at 3 T, whereas delayed-enhancement, flow quantification, and black-blood sequences are comparable at 1.5 T and 3 T. Knowledge of the relevant physics helps in identifying artifacts and modifying sequences to optimize image quality. Online supplemental material is available for this article.

7th International Workshop on Osteoarthritis Imaging report: "imaging in OA--now is the time to move ahead"

The 7th Osteoarthritis Research Society International (OARSI) International Workshop on Osteoarthritis Imaging was held in Reykjavik, Iceland, from July 9-12, 2014; attracting attendees from academia, pharmaceutical and Magnetic resonance imaging (MRI) industries, as well as a large number of young investigators. The Workshop program consisted of six modules, including imaging in osteoarthritis (OA), imaging and pain in OA, new techniques in imaging, risk factors and structural outcomes, anti-nerve growth factor (a-NGF) therapy, and joint replacement. A wealth of data was presented from OA researchers from all over the world and participants gained insightful knowledge on up-to-date research work focusing on imaging of OA. This paper presents a summary of the salient points from the workshop.

CONCLUSIONS

Identifying the appropriate imaging modality and parameters will be critical for ensuring responsive, reproducible and reliable outcomes for clinical trials. Continued efforts from the OA research community are needed to establish the most effective use of imaging in OA clinical trials, including anti-NGF therapy and joint replacement trials, and to validate newer imaging techniques such as compositional MRI for use in the future clinical trials.

High-field MR imaging in pediatric congenital heart disease: initial results

BACKGROUND

Comprehensive assessment of pediatric congenital heart disease (CHD) at any field strength mandates evaluation of both vascular and dynamic cardiac anatomy for which diagnostic quality contrast-enhanced magnetic resonance angiography (CEMRA) and cardiac cine are crucial.

OBJECTIVE

To determine whether high-resolution (HR) CEMRA and steady-state free precession (SSFP) cine can be performed reliably at 3.0 T in children with CHD and to compare the image quality to similar techniques performed at 1.5 T.

MATERIALS AND METHODS

Twenty-eight patients with a median age of 5 months and average weight 9.0 ± 7.8 kg with suspected or known CHD were evaluated at 3.0 T. SSFP cine (n = 86 series) and HR-CEMRA (n = 414 named vascular segments) were performed and images were scored for image quality and artifacts. The findings were compared to those of 28 patients with CHD of similar weight who were evaluated at 1.5 T.

RESULTS

Overall image quality on HR-CEMRA was rated as excellent or good in 96% (397/414) of vascular segments at 3.0 T (k = 0.49) and in 94% (349/371) of vascular segments at 1.5 T (k = 0.36). Overall image quality of SSFP was rated excellent or good in 91% (78/86) of cine series at 3.0 T (k = 0.55) and in 81% (87/108) at 1.5 T (k = 0.47). Off-resonance artifact was common at both field strengths, varied over the cardiac cycle and was more prevalent at 3.0 T. At 3.0 T, off-resonance dark band artifact on SSFP cine was absent in 3% (3/86), mild in 69% (59/86), moderate in 27% (23/86) and severe in 1% (1/86) of images; at 1.5 T, dark band artifact was absent in 16% (17/108), mild in 69% (75/108), moderate in 12% (13/108) and severe in 3% (3/108) of cine images. The signal-to-noise ratio and contrast-to-noise ratio of both SSFP cine and HR-CEMRA images were significantly higher at 3.0 T than at 1.5 T (P < 0.001).

CONCLUSION

Signal-to-noise ratio and contrast-to-noise ratio of high-resolution contrast-enhanced magnetic resonance angiography and SSFP cine were higher at 3.0 T than at 1.5 T. Artifacts on SSFP cine were cardiac phase specific and more prevalent at 3.0 T such that frequency-tuning was required in one-third of exams. In neonates, high spatial resolution CEMRA was highly reliable in defining extracardiac vascular anatomy.

Dual-source parallel radiofrequency transmission for magnetic resonance breast imaging at 3T: any added clinical value?

PURPOSE

To investigate the influence of dual-source parallel radiofrequency (RF) excitation on clinical breast MR images.

METHODS

A 3T MR system with both dual-source and conventional single-source RF excitations was used to examine 22 patients. Axial TSE-T2WI with fat suppression, TSE-T1WI without fat suppression, THRIVE (3D field echo) and DWI (SE-EPI) were obtained by using both excitation techniques. Image homogeneity, image contrast and lesion conspicuity were measured or independently scored by two radiologists and were compared by paired-sample t test or Wilcoxon test.

RESULTS

Both excitations revealed 24 lesions. For SE sequences using dual-source mode, image homogeneity was improved (P=0.00), scan time was reduced, and ghost artifacts on DWI were significantly reduced (P=0.00). However, image contrast was not increased and lesion conspicuity had no significant difference between two modes, except DWI on which lesion conspicuity was significantly improved (P=0.00), due to less ghost artifacts. For field-echo sequence, image homogeneity, acquisition time, image contrast and lesion conspicuity had no significant difference between the two modes.

CONCLUSIONS

Dual-source parallel RF transmission has some added value for improving breast image quality. However, its value is limited in terms of improving lesion detection and characterization.

Feasibility of T2 -weighted turbo spin echo imaging of the human prostate at 7 tesla

PURPOSE

To demonstrate that high quality T2 -weighted (T2w) turbo spin-echo (TSE) imaging of the complete prostate can be achieved routinely and within safety limits at 7 T, using an external transceive body array coil only.

METHODS

Nine healthy volunteers and 12 prostate cancer patients were scanned on a 7 T whole-body system. Preparation consisted of B0 and radiofrequency shimming and localized flip angle calibration. T1 and T2 relaxation times were measured and used to define the T2w-TSE protocol. T2w imaging was performed using a TSE sequence (pulse repetition time/echo time 3000-3640/71 ms) with prolonged excitation and refocusing pulses to reduce specific absorption rate.

RESULTS

High quality T2w TSE imaging was performed in less than 2 min in all subjects. Tumors of patients with gold-standard tumor localization (MR-guided biopsy or prostatectomy) were well visualized on 7 T imaging (n = 3). The number of consecutive slices achievable within a 10-g averaged specific absorption rate limit of 10 W/kg was ≥28 in all subjects, sufficient for full prostate coverage with 3-mm slices in at least one direction.

CONCLUSION

High quality T2w TSE prostate imaging can be performed routinely and within specific absorption rate limits at 7 T with an external transceive body array.

Bilateral Evaluation of the Hand and Wrist in Untreated Early Inflammatory Arthritis: A Comparative Study of Ultrasonography and Magnetic Resonance Imaging

Objective.

To compare Doppler ultrasound (US) and 3.0-Tesla magnetic resonance imaging (3.0-T MRI) findings of synovial inflammation in the tendons and joints in an early polyarthritis cohort (patients who presented < 1 year after arthritis onset) using a bilateral hand and wrist evaluation. Also, to evaluate the diagnostic performance of US and MRI findings for rheumatoid arthritis (RA), their ability to predict RA as a diagnostic outcome, and their capacity to improve the accuracy of the 2010 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) RA classification criteria in early arthritis.

Methods.

Forty-five patients (40 women, 5 men; mean age 45.6 yrs) with untreated recent-onset polyarthritis participated in this prospective study and were examined using an US and MRI approach including both wrists and hands. After a followup of 12 months, patients were classified as having RA if they fulfilled the criteria for RA. The proportion of synovitis identified by US and MRI for each joint and tendon region was compared by chi-square test. The diagnostic performance of US and MRI for RA identification was evaluated using receiver-operating curve (ROC) analysis. Possible associations between synovitis for each joint and tendon region as identified by US or MRI and RA diagnosis at 12 months were tested by logistic regression analysis. The diagnostic performance of the ACR/EULAR RA classification criteria corrected by US and MRI joint and tendon counts was evaluated using ROC analysis.

Results.

Thirty patients fulfilled the ACR/EULAR criteria [early RA (ERA) patients] and the remaining 15 failed to meet these criteria (non-RA). Carpal joint synovitis and tenosynovitis of the flexor tendons was found in 86.7% and 86.7% of patients with ERA on MRI compared with 63.3% and 50% on US, respectively (p < 0.05). The global MRI and US counts revealed a good diagnostic performance for RA diagnosis of both techniques, although MRI was statistically significantly better [area under the curve (AUC) = 0.959 and AUC = 0.853, respectively; z statistic = 2.210, p < 0.05]. MRI identification of carpal joint synovitis (OR 3.64, 95% CI 1.119–11.841), tenosynovitis of the flexor tendons (OR 5.09, 95% CI 1.620–16.051), and global joint and tendon count (OR 2.77, 95% CI 1.249–6.139) were in the multivariate logistic regression model the most powerful predictors of progression toward RA. In the group of ERA patients with US joint and tendon counts ≤ 10, a statistically significant difference was found between the diagnostic performance for RA of the ACR/EULAR criteria as previously described and the diagnostic performance of the MRI-corrected ACR/EULAR criteria (AUC = 0.898 and AUC = 0.986, respectively; z statistic = 2.181, p < 0.05).

Conclusion.

3.0-T MRI identified a higher prevalence of synovitis in comparison to US in an early polyarthritis cohort. Both techniques have good diagnostic performance for RA although MRI reveals a significantly higher diagnostic capability. Synovitis of carpal joints and of flexor tendons as identified by MRI were the most powerful predictors of progression toward RA. In patients with US joint and tendon counts ≤ 10, MRI can significantly improve the diagnostic performance of the 2010 ACR/EULAR classification criteria.

7 Tesla MPRAGE imaging of the intracranial arterial vasculature: nonenhanced versus contrast-enhanced

PURPOSE

To intraindividually compare the delineation of intracranial arterial vasculature in nonenhanced versus contrast-enhanced magnetization prepared rapid gradient echo (MPRAGE) imaging at 7 Tesla (T).

MATERIALS AND METHODS

Sixteen subjects were examined on a 7 T whole-body magnetic resonance system (Magnetom 7T) equipped with a 32-channel transmit/receive head coil. MPRAGE imaging was performed pre- and postcontrast after the application of 0.1 mmol/kg bodyweight gadobutrol. For qualitative analysis, the delineation of the intracranial arteries, overall image quality, and image impairment were assessed in the nonenhanced and contrast-enhanced datasets using a 5-point scale (5 = excellent to 1 = nondiagnostic). Additionally, contrast ratios (CR) of the middle cerebral artery in correlation to surrounding gray matter in nonenhanced and postcontrast images were obtained. For statistical analysis a Wilcoxon signed-rank test was applied.

RESULTS

Nonenhanced MPRAGE imaging offered an excellent delineation of the central vessel segments of the anterior circulation (mean anterior circulation 4.6) and a moderate- to high-quality assessment of the vessels of the posterior circulation (mean posterior circulation 3.9). Vessel delineation was improved in all assessed segments in the contrast-enhanced datasets, except for the cavernous segment of the internal carotid artery. Quantitative analysis revealed a mild, nonsignificant increase in CR mean values of the M1 segment (CRnonenhanced 0.67; CRcontrast-enhanced 0.69).

CONCLUSION

Our results demonstrate the high diagnostic value of nonenhanced 7 T MPRAGE imaging for the assessment of the intracranial arterial vasculature, with improved assessment of the peripheral segments because of the application of a contrast agent.

Visualizing the prostate gland by MR imaging in young and old mice

PURPOSE

Prostate imaging requires optimization in young and old mouse models. We tested which MR sequences and field strengths best depict the prostate gland in young and old mice; and, whether prostate MR signal, size, and architecture change with age.

TECHNIQUE

Magnetic resonance imaging (MRI) of the prostate of young (2 months) and old (18 months) male nude mice (n = 6) was performed at 4.7 and 7 T and SCID mice (n = 6) at 7 T field strengths, using T1, fat suppressed T1, DWI, T2, fat suppressed T2, as well as T2-based- and proton density-based Dixon "water only" sequences. Images were ranked for best overall sequence for prostate visualization, prostate delineation, and quality of fat suppression. Prostate volume and signal characteristics were compared and histology was performed.

RESULTS

T2-based-Dixon "water only" images ranked best overall for prostate visualization and delineation as well as fat suppression (n = 6, P<0.001) at both 4.7 T and 7 T in nude and 7T in SCID mice. Evaluated in nude mice, T2-based Dixon "water only" had greater prostate CNR and lower fat SNR at 7 T than 4.7 T (P<0.001). Prostate volume was less in older than younger mice (n = 6, P<0.02 nude mice; n = 6, P<0.002 SCID mice). Prostate T2 FSE as well as proton density-based and T2-based-Dixon "water only" signal intensity was higher in younger than older mice (P<0.001 nude mice; P<0.01 SCID mice) both at 4.7 and 7 T. This corresponded to an increase in glandular hyperplasia in older mice by histology (P<0.01, n = 6).

CONCLUSION

T2-based Dixon "water only" images best depict the mouse prostate in young and old nude mice at 4.7 and 7 T. The mouse prostate decreases in size with age. The decrease in T2 and T2-based Dixon "water only" signal with age corresponds with glandular hyperplasia. Findings suggest age should be an important determinant when choosing models of prostate biology and disease.

Liver MRI at 3.0 tesla: comparison of image quality and lesion detectability between single-source conventional and dual-source parallel radiofrequency transmissions

OBJECTIVE

To prospectively and intraindividually compare liver magnetic resonance imaging (MRI) using single-source and dual-source parallel radiofrequency (RF) transmissions at 3.0-T for image quality, lesion detectability, and lesion contrast.

METHODS

Ninety-nine patients with 139 liver lesions underwent liver MRI at 3.0-T. Two radiologists performed a consensus review of T2-weighted images (T2WI), heavily T2WI (HT2WI), gadoxetic acid-enhanced hepatobiliary images, and diffusion-weighted imaging using single-source and dual-source RF transmissions with regard to image quality and lesion detectability. Contrast ratios between liver lesions and liver parenchyma were also calculated.

RESULTS

Image quality was better with dual-source than with single-source at T2WI and HT2WI (P < 0.05), but lesion detectabilities were similar for all sequences. There was no significant difference in mean contrast ratios for all sequences (P > 0.05).

CONCLUSION

Dual-source RF transmission provides a better image quality with T2WI and HT2WI than with single-source. However, 2 techniques showed similar lesion detectability.

Ocular volumetry using fast high-resolution MRI during visual fixation

BACKGROUND AND PURPOSE

Volumetry may be useful for evaluating treatment response and prognosis of intraocular lesions. Phantom, volunteer, and patient studies were performed to determine whether ocular MR volumetry is reproducible.

MATERIALS AND METHODS

Half-Fourier single-shot RARE and FSPGR sequences at 1.5T with a 76-mm-diameter surface coil were optimized to obtain still ocular images. Volumetry accuracies of each sequence were compared with simulated subretinal phantom volumes. Ocular volumetry was performed in 15 volunteers twice in 1 week by using contiguous axial images of the globes while the subjects stared at a target, and images were acquired in 2 seconds before the subjects were instructed to blink, with this process repeated as necessary. Imaging, intraobserver, and interobserver reproducibility for volumes of the whole eyeball and anterior chamber were assessed. Ocular volumetry was also performed in 6 patients with intraocular tumors before and after treatment.

RESULTS

The phantom study demonstrated that measurement error rates with RARE were significantly lower than with FSPGR (P<.01). The volunteer study demonstrated excellent imaging and intraobserver reproducibility of RARE volumetry for whole eyeballs and anterior chambers (P<.01). Although no interobserver differences were observed in anterior chamber volume measurement (P=.33), there was a significant difference between the 2 observers in eyeball volume measurement (P<.01). Follow-up volumetric data were useful for treatment decisions in all patients.

CONCLUSIONS

Ocular volumetry from contiguous ultrafast RARE images obtained during visual fixation is feasible in volunteer and patient studies and is superior to FSPGR images.

Diagnostic accuracy of ultra-high-b-value 3.0-T diffusion-weighted MR imaging for detection of prostate cancer

PURPOSE

To investigate the diagnostic accuracy of 3.0-T diffusion-weighted imaging (DWI) for detection of prostate cancer by using different b-values.

METHODS

Seventy-three patients underwent magnetic resonance imaging (MRI) at 3.0 T. Three MRI sets were reviewed by two radiologists: MRI and DWI (b = 500 s/mm(2)) (protocol A), MRI and DWI (b = 1000 s/mm(2)) (protocol B), and MRI and DWI (b = 2000s/mm(2)) (protocol C). Areas under the receiver operating characteristic curve (AUCs) were calculated.

RESULTS

The mean of the AUCs in protocol C was larger than those in protocol A and in protocol B (P<.05).

CONCLUSION

DWI (b = 2000s/mm(2)) at 3.0 T can improve the diagnostic accuracy for detection of prostate cancer.

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.

In vivo proton MRS of normal pancreas metabolites during breath-holding and free-breathing

AIM

To characterize normal pancreas metabolites using in vivo proton magnetic resonance spectroscopy ((1)H MRS) at 3T under conditions of breath-holding and free-breathing.

MATERIALS AND METHODS

The pancreases of 32 healthy volunteers were examined using (1)H MRS during breath-holding and free-breathing acquisitions in a single-voxel point-resolved selective spectroscopy sequence (PRESS) technique using a 3T MRI system. Resonances were compared between paired spectra of the two breathing modes. Furthermore, correlations between lipid (Lip) content and age, body-mass index (BMI), as well as choline (Cho) peak visibility of the normal pancreas were analysed during breath-holding.

RESULTS

Twenty-nine pairs of spectra were successfully obtained showing three major resonances, Lip, Cho, cholesterol and the unsaturated parts of the olefinic region of fatty acids (Chol+Unsat). Breath-hold spectra were generally better, with higher signal-to-noise ratios (SNR; Z=-2.646, p=0.008) and Cho peak visible status (Z=-2.449, p=0.014). Correlations were significant between spectra acquired by the two breathing modes, especially for Lip height, Lip area, and the area of other peaks at 1.9-4.1ppm. However, the Lip resonance was significantly different between the spectra of the two breathing modes (p<0.05). In the breath-holding spectra, there were significant positive correlations between Lip peak height, area, and age (r=0.491 and 0.521, p=0.007 and 0.004), but not between Lip peak area and BMI. There was no statistical difference in Cho resonances between males and females. The Lip peak height and area were significantly higher in the Cho peak invisible group than in the Cho peak visible group (t=2.661 and 2.353, p=0.030 and 0.043).

CONCLUSION

In vivo(1)H MRS of the normal pancreas at 3T is technically feasible and can characterize several metabolites. (1)H MRS during breath-holding acquisition is superior to that during free-breathing acquisition.

Current problems and future opportunities of abdominal magnetic resonance imaging at higher field strengths

Introduction of high-field-strength whole-body MR scanners to clinical routine made abdominal magnetic resonance (MR) imaging widely available. Higher field strength provides improved signal yield, but other issues such as shorter wavelength and increased power deposition of radiofrequency in tissue must also be taken into account. This review describes current problems and future opportunities of abdominal MR imaging at 3.0 T under special consideration of relevant physical properties and technical challenges: impact of higher field strength on signal-to-noise ratio, Larmor frequency, and chemical shift effects are elucidated in detail. Furthermore, changes in longitudinal and transverse relaxation times as well as increased susceptibility effects at 3.0 T are reported. General safety issues and limitations in radiofrequency power deposition are discussed. Subsequently, implications of the previously mentioned changed MR properties at 3.0 T on clinical abdominal examinations applying different sequence types are described.

[Breast MRI: Artefacts and pitfalls]

Multiple artefacts and pitfalls may occur with breast MRI. Artefacts are secondary to the MR technique itself while pitfalls often are the result of human error. The most common artefacts include motion, pulsation, chemical shift and magnetic susceptibility. The most common pitfalls include improper contrast injection, poor patient positioning, improper placement of the ROI and improper characterization of physiological and iatrogenic contrast enhancement. The identification of these artefacts and pitfalls on breast MR images may reduce their impact or even eliminate them. The use of optimized protocols is necessary. It is important to explain to patients the sequence of the examination, ensure proper placement of the breasts in the coil and optimize the contrast injection. The ROI should always be placed over the most suspicious region of the lesion. Finally, it is recommended to perform the MRI during the second week of the menstrual cycle and to discontinue the use of HRT 2 months prior to scanning when possible.

Accuracy of perfusion MRI with high spatial but low temporal resolution to assess invasive breast cancer response to neoadjuvant chemotherapy: a retrospective study

Background

To illustrate that Breast-MRI performed in high spatial resolution and low temporal resolution (1 minute) allows the measurement of kinetic parameters that can assess the final pathologic response to neoadjuvant chemotherapy in breast cancer.

Methods

Breast-MRI was performed in 24 women before and after treatment. Eight series of 1.11 minute-duration were acquired with a sub-millimeter spatial resolution. Transfer constant (K^trans) and leakage space (V_e) were calculated using measured and theoretical Arterial Input Function (AIF). Changes in kinetic parameters after treatment obtained with both AIFs were compared with final pathologic response graded in non-responder (< 50% therapeutic effect), partial-responder (> 50% therapeutic effect) and complete responder. Accuracies to identify non-responders were compared with receiver operating characteristic curves.

Results

With measured-AIF, changes in kinetic parameters measured after treatment were in agreement with the final pathological response. Changes in V_e and K^trans were significantly different between non-(N = 11), partial-(N = 7), and complete (N = 6) responders, (P = 0.0092 and P = 0.0398 respectively). A decrease in V_e of more than -72% and more than -84% for K^trans resulted in 73% sensitivity for identifying non-responders (specificity 92% and 77% respectively). A decrease in V_e of more than -87% helped to identify complete responders (Sensitivity 89%, Specificity 83%). With theoretical-AIF, changes in kinetic parameters had lower accuracy.

Conclusion

There is a good agreement between pathological findings and changes in kinetic parameters obtained with breast-MRI in high spatial and low temporal resolution when measured-AIF is used. Further studies are necessary to confirm whether MRI contrast kinetic parameters can be used earlier as a response predictor to neoadjuvant chemotherapy.

Current Status and New Developments in Breast MRI

SUMMARY: Breast magnetic resonance imaging (MRI) is the most sensitive imaging modality for the detection of breast cancer. Its specificity is equivalent to that of mammography. Nowadays, breast MRI is an absolutely essential breast imaging method. Technical innovations allow dynamic contrast-enhanced (DCE) MRI of both breasts with high image quality. Thereby, DCE breast MRI should always be performed with regard to current standards. New quantitative techniques such as diffusion-weighted MRI are promising. However, they still have potential pitfalls, in particular with regard to the diagnosis of non-mass lesions and small breast lesions. Ongoing technical innovations can possibly help to further optimize breast MRI.

Focal liver lesions at 3.0 T: lesion detectability and image quality with T2-weighted imaging by using conventional and dual-source parallel radiofrequency transmission

PURPOSE

To prospectively compare T2-weighted single-shot turbo spin-echo (TSE) sequences performed with parallel and conventional radiofrequency (RF) transmission at 3.0 T for liver lesion detection, image quality, lesion conspicuity, and lesion contrast.

MATERIALS AND METHODS

After written informed consent and institutional review board approval, 52 consecutive patients (32 men, 20 women; mean age, 56.6 years ± 13.7 [standard deviation]) underwent routine magnetic resonance (MR) imaging with a clinical 3.0-T unit. Two independent readers reviewed images acquired with conventional and dual-source parallel RF transmission for detection of focal liver lesions, with separate reading of a third radiologist, including all available imaging findings, clinical history, and histopathologic findings, as reference. Image quality and lesion conspicuity were rated on five- and three-point evaluation scales, respectively. Contrast ratios between focal liver lesions and adjacent liver parenchyma were calculated. Significance was determined by using nonparametric Wilcoxon signed-rank and marginal homogeneity tests.

RESULTS

With the reference standard, 106 index lesions were identified in 22 patients. Detection rate significantly improved from 87% (92 of 106) to 97% (103 of 106) (reader 1) and from 85% (90 of 106) to 96% (102 of 106) (reader 2) with parallel RF transmission (reader 1, P = .0078; reader 2, P = .002). Quality of parallel RF transmission images was assigned scores significantly higher, compared with quality of conventional RF transmission images (mean for reader 1, 2.88 ± 0.73 vs 4.04 ± 0.44; mean for reader 2, 2.81 ± 0.72 vs 4.04 ± 0.39; P < .0001 for both). Lesion conspicuity scores were significantly higher on parallel RF transmission images, compared with conventional RF transmission images (mean for reader 1, 2.02 ± 0.64 vs 2.92 ± 0.27; mean for reader 2, 2.06 ± 0.67 vs 2.90 ± 0.30; P < .0001 for both). Contrast ratios were significantly higher with parallel RF transmission (P < .05).

CONCLUSION

Compared with conventional RF transmission, parallel RF transmission significantly improved liver lesion detection rate, image quality, lesion conspicuity, and lesion contrast.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101429/-/DC1.

Multiparametric MRI biomarkers for measuring vascular disrupting effect on cancer

Solid malignancies have to develop their own blood supply for their aggressive growth and metastasis; a process known as tumor angiogenesis. Angiogenesis is largely involved in tumor survival, progression and spread, which are known to be significantly attributed to treatment failures. Over the past decades, efforts have been made to understand the difference between normal and tumor vessels. It has been demonstrated that tumor vasculature is structurally immature with chaotic and leaky phenotypes, which provides opportunities for developing novel anticancer strategies. Targeting tumor vasculature is not only a unique therapeutic intervention to starve neoplastic cells, but also enhances the efficacy of conventional cancer treatments. Vascular disrupting agents (VDAs) have been developed to disrupt the already existing neovasculature in actively growing tumors, cause catastrophic vascular shutdown within short time, and induce secondary tumor necrosis. VDAs are cytostatic; they can only inhibit tumor growth, but not eradicate the tumor. This novel drug mechanism has urged us to develop multiparametric imaging biomarkers to monitor early hemodynamic alterations, cellular dysfunctions and metabolic impairments before tumor dimensional changes can be detected. In this article, we review the characteristics of tumor vessels, tubulin-destabilizing mechanisms of VDAs, and in vivo effects of the VDAs that have been mostly studied in preclinical studies and clinical trials. We also compare the different tumor models adopted in the preclinical studies on VDAs. Multiparametric imaging biomarkers, mainly diffusion-weighted imaging and dynamic contrast-enhanced imaging from magnetic resonance imaging, are evaluated for their potential as morphological and functional imaging biomarkers for monitoring therapeutic effects of VDAs.

Comparison of multi-echo and single-echo gradient-recalled echo sequences for SPIO-enhanced liver MRI at 3 T

AIM

To assess the utility of a T2*-weighted, multi-echo data imaging combination sequenced on superparamagnetic iron oxide (SPIO)-enhanced liver magnetic resonance imaging (MRI) using a 3 T system.

MATERIALS AND METHODS

Fifty patients underwent SPIO-enhanced MRI at 3 T using T2*-weighted, single-echo, gradient-recalled echo (GRE) sequences [fast imaging with steady precession; repetition time (TR)/echo time (TE), 126 ms/9 ms; flip angle, 30°] and multi-echo GRE (multi-echo data image combination) sequences (TR/TE, 186 ms/9 ms; flip angle, 30°). Three radiologists independently reviewed the images in a random order. The sensitivity and accuracy for the detection of focal hepatic lesions (a total of 76 lesions in 33 patients; 48 solid lesions, 28 non-solid lesions) were compared by analysing the area under the receiver operating characteristic curves. Image artefacts (flow artefacts, susceptibility artefacts, dielectric artefacts, and motion artefacts), lesion conspicuity, and overall image quality were evaluated according to a four-point scale: 1, poor; 2, fair; 3, good; 4, excellent. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the lesions were compared.

RESULTS

Image artefacts were more frequent with single-echo GRE (p<0.05). The mean scale of image quality assessment for flow, susceptibility, dielectric, and motion artefacts were 2.76, 3.13, 3.42, and 2.89 with single-echo, respectively, compared with 3.47, 3.43, 3.47, and 3.39, respectively, with multi-echo GRE. There was no significant difference in lesion conspicuity between single-echo (3.15) and multi-echo (3.30) GRE sequences. The overall image quality was significantly (p<0.05) better with multi-echo (3.37) than with single-echo GRE (2.89). The mean SNR and CNR of the lesions were significantly (p<0.05) higher on multi-echo (79±23 and 128±59, respectively) images than on single-echo (38±11 and 102±44, respectively) images. Lesion detection accuracy and sensitivity were not significantly different between the two sequences. Mean accuracies and sensitivities were 0.864 and 0.785 for single-echo and 0.847 and 0.785 for multi-echo GRE, respectively.

CONCLUSION

At 3 T, the T2*-weighted, multi-echo data image combination sequence performs comparably to the T2*-weighted, single-echo GRE sequence for SPIO-enhanced MRI with good overall image quality and a decrease in undesired artefacts.

Cardiovascular magnetic resonance at 3.0 T: current state of the art

There are advantages to conducting cardiovascular magnetic resonance (CMR) studies at a field strength of 3.0 Telsa, including the increase in bulk magnetization, the increase in frequency separation of off-resonance spins, and the increase in T1 of many tissues. However, there are significant challenges to routinely performing CMR at 3.0 T, including the reduction in main magnetic field homogeneity, the increase in RF power deposition, and the increase in susceptibility-based artifacts.In this review, we outline the underlying physical effects that occur when imaging at higher fields, examine the practical results these effects have on the CMR applications, and examine methods used to compensate for these effects. Specifically, we will review cine imaging, MR coronary angiography, myocardial perfusion imaging, late gadolinium enhancement, and vascular wall imaging.

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.

Current and future trends in magnetic resonance imaging assessments of the response of breast tumors to neoadjuvant chemotherapy

The current state-of-the-art assessment of treatment response in breast cancer is based on the response evaluation criteria in solid tumors (RECIST). RECIST reports on changes in gross morphology and divides response into one of four categories. In this paper we highlight how dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and diffusion-weighted MRI (DW-MRI) may be able to offer earlier, and more precise, information on treatment response in the neoadjuvant setting than RECIST. We then describe how longitudinal registration of breast images and the incorporation of intelligent bioinformatics approaches with imaging data have the potential to increase the sensitivity of assessing treatment response. We conclude with a discussion of the potential benefits of breast MRI at the higher field strength of 3T. For each of these areas, we provide a review, illustrative examples from clinical trials, and offer insights into future research directions.

Cancer imaging: novel concepts in clinical magnetic resonance imaging

Cancer is a major public health problem in the Western world. Imaging is of crucial importance in oncology, because it may reduce cancer-related morbidity and mortality. To improve tumour evaluation, there is a need for functional imaging modalities that go beyond gross assessment of anatomical abnormalities and allow visualization and quantification of biochemical processes in vivo. Magnetic resonance imaging (MRI) not only provides anatomical information, but also offers a wide range of functional sequences that may aid the evaluation of cancerous lesions. Furthermore, MRI provides the opportunity to guide and monitor anticancer therapies noninvasively. The aim of this review is to highlight some of the most promising developments of MRI in the functional assessment of cancer and the guidance and monitoring of (novel) anticancer therapies.

Magnetic resonance angiography of abdominal vessels at 3 T

Magnetic resonance angiography (MRA) has evolved significantly since first described in the early 1990s. Unrivaled image quality and freedom from artifacts has made it a reliable and widely utilized technique. Imaging at 3 T offers the potential for higher resolutions images with better temporal resolution compared to 1.5 T. This article will review the technique and contrast agents required to perform MRA at 3 T and the relevant clinical applications. We also discuss non-contrast enhanced MRA in the era of nephrogenic systemic fibrosis and future prospect for MRA at 3 T.

Whole-body MR imaging, bone diffusion imaging: how and why?

Whole-body MRI (W-B MRI) and diffusion-weighted imaging (DWI) are two novel techniques that greatly facilitate the evaluation of many disorders of childhood. In the musculoskeletal system, these techniques primarily aid in the evaluation of the marrow, although there is increasing interest in the study of soft-tissue abnormalities with W-B MRI and of cartilage with DWI.The normal pattern of marrow transformation affects both modalities throughout childhood. Haematopoietic marrow has a much higher signal intensity than fatty marrow on W-B MRI short tau inversion recovery (STIR) images (Darge et al. Eur J Radiol 68:289-298, 2008). Diffusion is greater in haematopoietic marrow than in fatty marrow and decreases in the skeleton with age (Jaramillo et al. Pediatr Radiol 34:S48, 2004). It is important therefore to remember that the entire skeleton is haematopoietic at birth and that there is a process of marrow transformation to fatty marrow. Marrow conversion proceeds from the fingers to the shoulders and from the toes to the hips. Within each bone, fatty marrow transformation begins in the epiphyses, and within the shaft of the long bones fatty marrow transformation begins at the diaphysis and proceeds towards the metaphyses.

In vitro evaluation of MR imaging issues at 3T for aneurysm clips made from MP35N: Findings and information applied to 155 additional aneurysm clips

BACKGROUND AND PURPOSE

Aneurysm clips need to be tested at 3T to characterize MR imaging concerns, including magnetic field interactions, MR imaging-related heating, and artifacts. Therefore, we evaluated these risks for aneurysm clips.

MATERIALS AND METHODS

Three different MP35N aneurysm clips (Codman Slim-Line Aneurysm Clip, straight, blade length 25-mm; Codman Slim-Line Aneurysm Clip Graft, 5-mm diameter x 5-mm width; Codman Slim-Line Aneurysm Clip, reinforcing 30 degrees angle, 6-mm x 18-mm) that represented the largest mass for 155 additional clips made from MP35N were tested. The clips were evaluated at 3T for magnetic field interactions, heating, and artifacts. We studied MR imaging-related heating, placing the clip in a gelled-saline-filled phantom with MR imaging performed by using a transmit/receive radio-frequency body coil at a whole-body average SAR of 3 W/kg for 15 minutes. Artifacts were characterized by using T1-SE and GRE pulse sequences.

RESULTS

Each aneurysm clip showed relatively minor magnetic field interactions, which would not cause movement in situ. Heating was not excessive (highest temperature change, <1.8 degrees C). Artifacts may create problems if the area of interest is in the same area or close to the aneurysm clip.

CONCLUSIONS

The results of this investigation demonstrated that it would be acceptable (ie, "MR conditional" using current terminology) for patients with these aneurysm clips to undergo MR imaging at < or =3T. Notably, on the basis of the sizes of the clips that underwent testing, these findings pertain to 155 additional aneurysm clips made from the same material.

DeltaR2* in fetal sheep brains during hypoxia: MR imaging at 3.0 T versus that at 1.5 T

PURPOSE

To investigate the feasibility of fetal blood oxygen level-dependent magnetic resonance (MR) imaging at 1.5 T and to compare DeltaR2* in the brains of fetal sheep during hypoxia at 3.0 T with that at 1.5 T.

MATERIALS AND METHODS

All experimental protocols were reviewed and approved by the local authorities on animal protection. Between January 2006 and May 2006, fetal brain measurements were performed in eight pregnant ewes with 1.5-T and 3.0-T MR imaging units after fetal paralysis was achieved by administering pancuronium bromide. With both imaging units, a T2*-weighted single-shot gradient-echo echo-planar imaging sequence (echo time, 30 msec at 3.0 T and 50 msec at 1.5 T) was used to measure T2* signal changes (DeltaR2*) in the fetal brain in control conditions and during hypoxia (maternal oxygenation, 50%-70%). A carotid catheter was placed and maintained in the fetuses to enable measurement of the fetal arterial oxygen saturation (SaO(2)). DeltaR2* was correlated with fetal SaO(2), and linear regression analysis was performed. A paired t test was used to evaluate differences, with a significance level of P < .05.

RESULTS

At both field strengths, a signal intensity decrease on T2*-weighted images during hypoxia was detected. At 1.5 T, mean fetal SaO(2) was reduced from 65.4% +/- 9.2 (standard deviation) during control conditions to 17.7% +/- 6.2 during hypoxia. DeltaR2* and fetal SaO(2) correlated significantly (r = 0.98, P = .018). At 3.0 T, fetal SaO(2) was reduced from 62.4% +/- 7.5 during control conditions to 18% +/- 7.5 during hypoxia. DeltaR2* and fetal SaO(2) also correlated significantly (r = 0.95, P = .012). A linear fit resulted in a slope value of 0.084 +/- 0.003 for 1.5 T and 0.166 +/- 0.016 for 3.0 T. This means a doubled sensitivity of DeltaR2* for oxygen saturation variations at 3.0 T compared with 1.5 T.

CONCLUSION

MR imaging at 3.0 T is more sensitive than that at 1.5 T in the detection of DeltaR2* in the fetal brain during hypoxia. However, there was a signal decrease in the fetal brain in all 1.5-T experiments during hypoxia. Thus it is possible to measure fetal DeltaR2* at 1.5 T, which may be of more practical relevance for the evaluation of pregnant women.

MRI safety update 2008: part 2, screening patients for MRI

OBJECTIVE

This article is the second part of a two-part series on MRI safety. In this article, part 2, the topic of screening patients for MRI procedures is addressed.

CONCLUSION

To prevent incidents and accidents associated with MRI, it is necessary to regularly revisit the safety topics that directly impact patient management especially with respect to the subjects that are "new," those that should be reassessed because of recent changes, topics that deserve emphasis because of controversy or confusion, and information that should be considered in light of new findings.