Whole‐heart contrast‐enhanced coronary magnetic resonance angiography using gradient echo interleaved EPI

Whole‐heart coronary MR angiography (MRA) is a promising method for detecting coronary artery disease. However, the imaging time is relatively long (on the order of 10–15 min). Such a long imaging time may result in patient discomfort and compromise the robustness of whole‐heart coronary MRA due to increased respiratory and cardiac motion artifacts. The goal of this study was to optimize a gradient echo interleaved echo planar imaging (GRE‐EPI) acquisition scheme for reducing the imaging time of contrast‐enhanced whole‐heart coronary MRA. Numerical simulations and phantom studies were used to optimize the GRE‐EPI sequence parameters. Healthy volunteers were scanned with both the proposed GRE‐EPI sequence and a 3D TrueFISP sequence for comparison purposes. Slow infusion (0.5 cc/sec) of Gd‐DTPA was used to enhance the signal‐to‐noise ratio (SNR) of the GRE‐EPI acquisition. Whole‐heart images with the GRE‐EPI technique were acquired with a true resolution of 1.0 × 1.1 × 2.0 mm³ in an average scan time of 4.7 ± 0.7 min with an average navigator efficiency of 44 ± 6%. The GRE‐EPI acquisition showed excellent delineation of all the major coronary arteries with scan time reduced by a factor of 2 compared with the TrueFISP acquisition. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Magnetic resonance imaging of the brain with gadopentetate dimeglumine-DTPA: Comparison of T1-weighted spin-echo and 3D gradient-echo sequences

Short TR, short TE, high resolution, 3D gradient-recalled echo (GRE) imaging was evaluated for lesion detection in the brain. High resolution 3D GRE data acquisition was used to reduce partial volume effects and flow artifacts, to better visualize smaller structures, to minimize signal losses caused by field inhomogeneities, and to allow better image reformatting. Spin-echo (SE) and 3D GRE approaches were compared for lesion detection after the administration of an MR contrast agent, gadopentetate dimeglumine. Preliminary clinical studies demonstrated that the signal-to-noise ratio (SNR) in each slice of the GRE scan was worse than that of the SE scan because of the much thicker slices acquired with the SE technique. However, by averaging two adjacent 3D slices, the SNR of the two methods was essentially equivalent. In the averaged GRE slices, large lesions were seen just as well as in the SE images. More importantly, small lesions were better visualized in the thin 3D GRE images than in the thick SE images for the lesions studied in this work and the protocols used. These observations were confirmed by theoretical simulations.     

First-pass contrast-enhanced inversion recovery and driven equilibrium fast gre imaging studies: Detection of acute myocardial ischemia

The purpose of this study was (1) to monitor the dynamic effects Of T1 -enhancing and magnetic SUSCCPtibility contrast material on normal canine myocardium using inversion recovery (IR)- and driven equilibrium @E)-prepared fast gradient-recalled echo (GRE) sequences and (2) to determine the relative value of T1-enhancing and magnetic eusceptibflity contrast material in detecting regions of ischemia in the same animal. Normal dogs (n = 5) and dogs with acute occlusion of the left anterior descending (LAD] coronary artery [n = 11) were studied using a 1.5-T NIR imager. ECG-gated fast IR-prepared GRE images were acquired using TI/TR/TE of 700/7.0/2.9 msec and a flip angle of 7°. Fast DE-prepared GRE images were obtained using a flip angle of 12° and a DE delay /TR/TE of 60/10.2/4.2 msec. Sequential images were acquired to monitor transit of 0.06 mmol/kg gadodiamide injection and 0.2 and 0.4 mmol/kg sprodiamide injection. On slice-nonselective IR fast GRE images. gadodiamide caused signiflcant enhancement of the normal myocardium and the left ventricular (LV) chamber blood. In dogs with LAD occlusion, the ischemic region was defined as an area of low signal intensity (SI). On DE-prepared GRE sequences, administration of sprodiamide resulted in a substantial decrease in signal from normal myocardium and LV chamber blood in normal dogs. In animals subjected to LAD occlusion, this contrast medium produced a transient decrease in SI from normal myocardium [P <.06) and no signiflcant change in SI from ischemic myocardium. IR- and DE-prepared taet GRE imaging can be used to monitor the transit of Tl-enhancing and magnetic susceptibility contrast material in the heart. respectively. Cardiac image quality was much better when slice-nonselective IR-prepared fast GRE sequences were used rather than DE-prepared fast GRE.     

Synergistic effect between iron and gadolinium in MRI

Different combinations of iron glycerophosphate (Fe) and gadolinium-diethylene triamine pentaacetic acid (DTPA) (Gd) were imaged with a three-dimensional (3D) gradient-recalled echo (GRE), a 2D GRE, and a HASTE sequence on a 1.5-T MR scanner. A combination of Fe and Gd results in a synergistic effect, which improves the signal gain for selective 3D imaging of the colon and simultaneously decreases the endoluminal signal on the HASTE and 2D GRE images for better visualization of water and Gd-enhanced structures in the gut wall.     

Assessment and compensation of susceptibility artifacts in gradient echo MRI of hyperpolarized 3He gas.

The effects of macroscopic background field gradients upon 2D gradient echo images of inhaled (3)He in the human lung were investigated at 1.5 T. Effective compensation of in-slice signal loss in (3)He gradient echo images was then demonstrated using a multiple acquisition interleaved single gradient echo sequence. This method restores signal dephasing through a combination of separate images acquired with different slice refocusing gradients. In vivo imaging of volunteers with the sequence shows substantial restoration of signal at the lung periphery and close to blood vessels. The technique presented may be useful when using (3)He MRI for volumetric measurements of lung ventilation and in studies using (3)He combined with intravenous contrast as a means of assessing lung ventilation/perfusion (V/Q).     

Detection of hepatic hypovascular metastases: 3D gradient echo MRI using a hepatobiliary contrast agent

Purpose:

To assess the diagnostic performance of gadobenate dimeglumine‐enhanced 3D gradient echo (3D‐GRE) magnetic resonance imaging (MRI) for the detection of hepatic hypovascular metastases.

Materials and Methods:

We retrospectively analyzed the initial radiologic reports of MRI of 41 patients with suspected hepatic metastases. Seventy‐nine metastatic lesions were confirmed by histopathology or intraoperative ultrasound (IOUS). The sensitivity and positive predictive values for the diagnosis of hepatic metastasis were determined among each MRI set (hepatobiliary phase, precontrast images, dynamic imaging). The diagnostic performance of dynamic image set and combined dynamic and hepatobiliary image set was also evaluated by two radiologists using alternative free response receiver operating characteristic (ROC) analysis.

Results:

The overall detection rate and positive predictive value of MR were 96.2% (76/79) and 96.2% (76/79), respectively. Images obtained with hepatobiliary phase 3D‐GRE showed a significantly better detection rate compared to those with precontrast sequences or dynamic imaging (P = 0.008 and 0.016, respectively). Regarding lesions 1 cm or smaller, the detection rate was 90.3% (28/31). Each reader showed a higher Az value of the combined hepatobiliary image set than those of the dynamic image set.

Conclusion:

3D‐GRE MRI using a hepatobiliary contrast agent is an accurate tool in the detection of hepatic hypovascular metastases and improves detection rate compared with precontrast and dynamic imaging. J. Magn. Reson. Imaging 2010;31:571–578. © 2010 Wiley‐Liss, Inc.     

Enhancement effects of hepatic dynamic MR imaging at 3.0 T and 1.5 T using gadoxetic acid in a phantom study: comparison with gadopentetate dimeglumine

To identify the optimum sequence at gadoxetic acid enhanced hepatic dynamic magnetic resonance imaging in the arterial phase, we studied phantoms that contained gadoxetic acid or gadopentetate dimeglumine diluted in human blood. We obtained magnetic resonance images at 3.0 T and 1.5 T with one vendor (Siemens) using 3D‐gradient echo (GRE)‐, 2D‐fast low angle shot (FLASH)‐, and turbo spin echo sequences. Contrast ratio was highest for 3D‐GRE; at both 3.0 T and 1.5 T it was superior when the contrast agent was gadoxetic acid. With both gadoxetic acid and gadopentetate dimeglumine, contrast ratio peaked at around 5‐and 2 mmol/L on 3D‐GRE‐ and 2D‐FLASH images, respectively. Compared with gadopentetate dimeglumine, at 3.0 T, the peak contrast ratio of gadoxetic acid was 14.1% better on 3D‐GRE images and 14.0% better on 2D‐FLASH images; at 1.5 T it was 16.4% better on 3D‐GRE‐ and 5.7% better on 2D‐FLASH images. With respect to the magnetic field strength, at 3.0 T the peak contrast ratio of gadoxetic acid was 6.0% better than at 1.5 T on 3D‐GRE images and 49.5% better on 2D‐FLASH images; it was 8.5% better on 3D‐GRE‐ and 44.6% better on 2D‐FLASH images than when the contrast agent was gadopentetate dimeglumine. Thus, gadoxetic acid yielded better enhancement on 3D‐GRE images acquired at 3.0 T than at 1.5 T and enhancement was better than that obtained with gadopentetate dimeglumine at the same concentration. Magn Reson Med 66:213–218, 2011. © 2011 Wiley‐Liss, Inc.     

High-resolution depiction of the cranial nerves in the posterior fossa (N III–N XII) with 2D fast spin echo and 3D gradient echo sequences at 3.0 T

PurposeThe objective of this study was to evaluate the influence of high-resolution imaging obtainable with the higher field strength of 3.0 T on the visualization of the brain nerves in the posterior fossa by using T₂-weighted fast spin echo (FSE) and fast imaging employing steady-state gradient echo (GRE) sequences as the most suitable techniques to visualize each of the cranial nerves.Materials and methodsIn total, 20 nerves were investigated on MR images of 12 volunteers each and selected for comparison, respectively, with the FSE sequences with 5-mm and 2-mm section thicknesses and GRE sequences acquired with a 3.0-T scanner and a quadrature head coil. The resulting MR images were evaluated by three independent readers who rated image quality according to depiction of anatomic detail and contrast with use of a rating scale.ResultsIn general, decrease of the slice thickness showed a significant increase in the detection of nerves as well as in the image quality characteristics. As expected, artifacts were prominent in high-field imaging of the posterior fossa with GRE sequences. Nevertheless, comparing FSE and GRE imaging, the course of brain nerves and brainstem vessels was visualized best with use of the three-dimensional (3D) pulse sequence, although with respect to structural identification and contrast according to the rating scale, observer scores were not significantly improved.ConclusionThe comparison revealed the clear advantage of a thin section. The increased resolution enabled immediate identification of all brainstem nerves. Although image quality is impaired at GRE at high field strength, this sequence most distinctly and confidently depicted pertinent structures and enables 3D reconstruction in order to illustrate complex relations of the brainstem.     

Noninvasive in vivo MRI detection of neuritic plaques associated with iron in APP[V717I] transgenic mice, a model for Alzheimer's disease.

Transgenic mice overexpressing the London mutant of human amyloid precursor protein (APP[V717I]) in neurons develop amyloid plaques in the brain, thus demonstrating the most prominent neuropathological hallmark of Alzheimer's disease. In vivo 3D T2*-weighted MRI on these mice (24 months of age) revealed hypointense brain inclusions that affected the thalamus almost exclusively. Upon correlating these MRI observations with a panel of different histologic staining techniques, it appeared that only plaques that were positive for both thioflavin-S and iron were visible on the MR images. Numerous thioflavin-S-positive plaques in the cortex that did not display iron staining remained invisible to MRI. The in vivo detection of amyloid plaques in this mouse model, using the intrinsic MRI contrast arising from the iron associated with the plaques, creates an unexpected opportunity for the noninvasive investigation of the longitudinal development of the plaques in the same animal. Thus, this work provides further research opportunities for analyzing younger APP[V717I] mouse models with the knowledge of the final outcome at 24 months of age.     

Effects of iodinated contrast and field strength on gadolinium enhancement: implications for direct MR arthrography

PURPOSE: To optimize direct magnetic resonance (MR) arthrography by determining the effect of dilution of gadolinium in iodinated contrast, saline, or albumin on T1-weighted, T2-weighted, and gradient-recalled echo (GRE) images, and the effect of scanner field strength. MATERIALS AND METHODS: Gadopentetate dimeglumine was diluted into normal saline, albumin, or iodinated contrast (0.625 mmol/liter to 40 mmol/liter). Samples were scanned at 1.5T and 0.2T. Signal intensity was measured using T1-weighted spin-echo (SE), T2-weighted SE, and two- and three-dimensional GRE (20 degrees-75 degrees flip angle) sequences. Graphical analysis of signal intensity vs. gadolinium concentration was performed. RESULTS: Albumin had no effect on gadolinium contrast. Dilution of gadolinium in iodinated contrast decreased signal intensity on all sequences compared to samples of identical concentration diluted in saline at both 1.5T and 0.2T: with a 2 mmol/liter gadolinium solution at 1.5T, signal was decreased by 26.1% on T1-weighted images, 31.7% on GRE20 images, and 28.9% on GRE45 images, and the T2 value decreased by 71.1%; at 0.2T, signal was decreased by 23.5% on T1-weighted images. On all sequences, the peak signal shifted to the left (lower gadolinium concentration) when diluted in iodinated contrast. Peak signal was also seen at different gadolinium concentrations on different sequences and field strength: at 1.5T, peak in saline/iodine was 2.5/0.625 mmol/liter on T1-weighted images, and 2.5/1.25 mmol/liter on GRE20 and GRE45 sequences. At 0.2T, peak in saline/iodine was 0.625-2.5/1.25 mmol/liter on T1-weighted images, 0.625-2.5/1.25 on GRE45 images, 2.5-10.0/1.25-5.0 mmol/liter on GRE65 images, and 1.25-5.0/0.625-1.25 mmol/liter on GRE75 images. CONCLUSION: Dilution of gadolinium in iodinated contrast results in decreased signal on T1-weighted, T2-weighted, and GRE images compared to dilution in saline or albuminfor both 1.5-T and 0.2-T scanners; if gadolinium is diluted in iodinated contrast for MR arthrography, a lower concentration should be used because the peak is shifted to the left. The use of iodinated contrast should be minimized, as it may diminish enhancement and lower the sensitivity and specificity of MR arthrography. Optimal gadolinium concentration for MR arthrography is dependent on scanner field strength and a broader range of gadolinium concentration can be used to provide maximal signal at low field strength.     

Differentiation of nonmetastatic and metastatic rodent prostate tumors with high spectral and spatial resolution MRI.

MR images can be acquired with high spectral and spatial resolution to precisely measure lineshapes of the water and fat resonances in each image voxel. Previous work suggests that the high-resolution spectral information can be used to improve image contrast, SNR, sensitivity to contrast agents and to physiologic and biochemical processes that affect local magnetic susceptibility gradients. The potential advantages of high-resolution spectroscopic imaging (SI) suggest that it might be useful for early detection and characterization of tumors. The present experiments evaluate the use of high-resolution SI to discriminate between metastatic and nonmetastatic rodent Dunning prostate tumors. SI datasets were obtained at 4.7 Tesla with an in-plane resolution of 350-500 micron in a single 1.0-mm slice, and 6-8 Hz spectral resolution, before and after i.v. injection of an iron oxide contrast agent. Images of water signal peak height in nonmetastatic tumors were smoother in the tumor interior than images of metastatic tumors (P <.004 by t-test) before contrast media injection. This difference was stronger in contrast-enhanced images (P <.0004). In addition, the boundary between the tumor and muscle was more clearly demarcated in nonmetastatic than metastatic tumors. Combinations of image texture, tumor edge morphology, and changes in T2* following contrast media injection improved discrimination between metastatic and nonmetastatic tumors. The data presented here do not demonstrate that effective discrimination between metastatic and nonmetastatic tumors depends on the use of high-resolution SI. However, the results suggest that SI and/or other MR methods that provide similar contrast might be used clinically for early and accurate detection of metastatic disease.     

MR imaging characterization of postischemic myocardial dysfunction („stunned myocardium”︁): Relationship between functional and perfusion abnormalities

Stunned myocardium has been detected in patients treated successfully with thrombolytic agents. The hypothesis of this study was that fast gradient echo (GRE) imaging could be used to characterize the regional functional and perfusion abnormalities that are indicative of myocardial stunning. This study was designed to monitor and correlate the extent of wall thickness and perfusion abnormalities as determined by fast (segmented k space) cine and contrast enhanced GRE imaging, respectively. Dogs were subjected to left circumflex (LCX) coronary artery occlusion (15 min) followed by 30-minute reperfusion (n = 8). Perivascular flow probes were used to continuously measure flow in left anterior descending (LAD) and LCX coronary arteries. Short-axis inversion recovery prepared fast GRE and cine images were acquired at baseline, at occlusion, and at 1, 10, and 30 minutes of reflow. Regional signal intensity and percent systolic wall thickening were determined at 26 equally spaced circumferential positions to compare the extent of functional and perfusion abnormalities. During occlusion and reperfusion, the ischemic region was demonstrated on contrast-enhanced images as a hypointense and hyperintense region, respectively. During occlusion, the extent of the perfusion defect (32% ± 2% of the circumference of the equatorial slice) correlated closely (r = .74) with the extent of contractile dysfunction (35% ± 2%). After reperfusion, there was transient recovery in the percent wall thickening (26% ± 4% vs 36% ± 4% normal), coinciding with the reactive hyperemic response, but this was followed by a significant decline in wall thickening at 10 minutes (19% ± 4%) and 30 minutes (12% ± 2%). Fast MR imaging may be useful to monitor postischemic myocardial abnormalities after thrombolytic therapy and the response to pharmacologic interventions.     

Myocardial first pass perfusion: steady-state free precession versus spoiled gradient echo and segmented echo planar imaging.

The imaging sequences used in first pass (FP) perfusion to date have important limitations in contrast-to-noise ratio (CNR), temporal and spatial resolution, and myocardial coverage. As a result, controversy exists about optimal imaging strategies for FP myocardial perfusion. Since imaging performance varies from subject to subject, it is difficult to form conclusions without direct comparison of different sequences in the same subject. The purpose of this study was to directly compare the saturation recovery SSFP technique to other more commonly used myocardial first pass perfusion techniques, namely spoiled GRE and segmented EPI. Differences in signal-to-noise ratio (SNR), CNR, relative maximal upslope (RMU) of signal amplitude, and artifacts at comparable temporal and spatial resolution among the three sequences were investigated in computer simulation, contrast agent doped phantoms, and 16 volunteers. The results demonstrate that SSFP perfusion images exhibit an improvement of approximately 77% in SNR and 23% in CNR over spoiled GRE and 85% SNR and 50% CNR over segmented EPI. Mean RMU was similar between SSFP and spoiled GRE, but there was a 58% increase in RMU with SSFP versus segmented EPI.     

Cine gradient refocused echo (GRE) imaging of intravascular masses: differentiation between tumor and nontumor thrombus.

Spin echo MR imaging has not permitted reliable differentiation between intraluminal blood clot and tumor thrombus. This study assessed the role of ECG referenced repetitive gradient refocused echo (cine GRE) imaging for the differentiation of intravascular tumor from blood clot. Cine GRE images were reviewed in 23 patients, 11 of whom had intravascular tumor and 12 of whom had intravascular blood clots. Percentage contrast between the lesion and skeletal muscle as the reference tissue was determined from a subjective review of the images and objective signal intensity measurements. Intravascular clots were found to be lower in signal intensity than muscle (mean -55 +/- 29%). Intravascular tumors showed higher signal intensity relative to muscle (mean +17 +/- 9%) with the exception of myxomas (n = 2), which had signal intensity values relative to muscle as low as clots (mean -41 +/- 17%). Three masses in the inferior vena cava were composed of central tumor and peripheral clot; the two components could be differentiated with cine GRE imaging. Cine GRE imaging provides adequate signal intensity differences to visualize intravascular masses and helps to differentiate intravascular clot from tumor thrombus. However, if the tumor contains substantial amounts of iron, then the signal is also low and consequently clot and thrombus may not be distinguishable. This can occur in some atrial myxomas.     

Suppression of intravascular signal on fat-saturated contrast-enhanced thoracic MR arteriograms

PURPOSE: To assess the prevalence of artifactual signal intensity loss within the aortic arch and proximal branch vessels on fat-saturated contrast material-enhanced magnetic resonance (MR) arteriograms of the thoracic aorta and to hypothesize about the cause of the loss of signal intensity. MATERIALS AND METHODS: Between January and June 1998, 105 consecutive MR arteriograms of the thoracic aorta were acquired in 103 patients at 1.5 T. Imaging included an arterial phase three-dimensional (3D) fat-saturated contrast-enhanced gradient-echo (GRE) sequence followed by a delayed two-dimensional (2D) transverse fat-saturated GRE sequence. All MR images were reviewed by two radiologists who were blinded to patient history and results of imaging studies and who evaluated the images for the presence of intraluminal loss of signal intensity in the aortic arch and the proximal branch vessels. RESULTS: Intravascular loss of signal intensity was present in at least one vessel on 23 of the 105 arterial phase 3D studies. Seventy-one of 91 left subclavian arterial segments had loss of signal intensity on the delayed 2D studies. CONCLUSION: Intravascular signal intensity loss can be present on contrast-enhanced fat-saturated images of the aortic arch and proximal branch vessels, particularly the left subclavian artery. This phenomenon, which is to the authors' knowledge previously unreported and which is hypothesized to result from undesired water saturation, should not be misinterpreted as stenotic or occlusive vascular disease.     

T1-weighted spoiled gradient-echo MR imaging of focal hepatic lesion: comparison of in-phase vs opposed-phase pulse sequence

The goal of our prospective study was to compare quantitatively and qualitatively in-phase and opposed-phase T1-weighted breath-hold spoiled gradient-recalled-echo (GRE) MR imaging technique for imaging focal hepatic lesion. Thirty-eight patients with 53 focal hepatic lesions had in-phase (TR = 12.3 ms, TE = 4.2 ms) and opposed-phase (TR = 10.1 ms, TE = 1.9 ms) GRE (flip angle = 30°, bandwidth ± 32 kHz, matrix size 256 × 128, one signal average) MR imaging at 1.5 T. Images were analyzed quantitatively by measuring the lesion-to-liver contrast and for lesion detection. In addition, images were reviewed qualitatively for lesion conspicuity. Quantitatively, lesion-to-liver contrast obtained with in-phase (3.22 ± 1.86) and opposed-phase pulse sequence (3.72 ± 2.32) were not statistically different (Student's t-test). No difference in sensitivity was found between in-phase and opposed-phase pulse sequence (31 of 53, sensitivity 58 % vs 30 of 53, sensitivity 57 %, respectively). Two lesions not seen with opposed-phase imaging were detected with in-phase imaging. Conversely, one lesion not seen on in-phase imaging was detected on opposed-phase imaging so that the combination of in-phase and opposed-phase imaging yielded detection of 32 of 53 lesions (sensitivity 60 %). Qualitatively, lesion conspicuity was similar with both techniques. However, in-phase images showed better lesion conspicuity than opposed-phase images in 9 cases, and opposed-phase images showed better lesion conspicuity than in-phase images in 7 cases. No definite advantage (at a significant level) emerged between in-phase and opposed-phase spoiled GRE imaging. Because differences in lesion conspicuity and lesion detection may be observed with the two techniques in individual cases, MR evaluation of patients with focal hepatic lesion should include both in-phase and opposed-phase spoiled GRE imaging. Received 30 October 1996; Revision received 6 January 1997; Accepted 8 January 1997     

MR imaging of the human hand and wrist at 7 T

Objective  The purpose of this study was to evaluate the feasibility, quality, and possible future implications of magnetic resonance imaging (MRI) of the human hand and wrist at 7 T. Materials and methods  Images of the left hand of a healthy volunteer were acquired with a 7- and a 1.5-T whole body system and comparatively analyzed. Axial and coronal two-dimensional gradient echo (GRE) images with inflow saturation, coronal 3D GRE images, and time-of-flight angiographies were obtained without averaging. Image details were related to the complex hand anatomy. Results  With the 7-T protocols established in this study, high-quality and high-resolution images of the hand and wrist were obtained. In the 2D GRE images at 7 T, small anatomical structures of the hand were depicted in vivo with superior detail and resolution, compared to 1.5 T and published studies at lower field strength. Signal-to-noise ratios (SNRs) were approximately five times higher at 7 T compared to 1.5 T. Additionally, thin 3D GRE images with good quality of the whole hand were obtained in a short acquisition time. Moreover, time-of-flight angiographies of the small hand arteries have been acquired without the application of contrast agents. Conclusion  Seven-tesla imaging of the hand can be used in vivo with ultra-high resolution and sufficient SNR. It allows for exact delineation of most anatomical structures including nerves, muscles, tendons, ligaments, cartilage, and blood vessels.     

Detection of hepatic metastases by superparamagnetic iron oxide-enhanced MR imaging: prospective comparison between 1.5-T and 3.0-T images in the same patients

Objective:

To prospectively compare the diagnostic performance of superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance (MR) imaging at 3.0 T and 1.5 T for detection of hepatic metastases.

Methods:

A total of 28 patients (18 men, 10 women; mean age, 61 years) with 80 hepatic metastases were prospectively examined by SPIO-enhanced MR imaging at 3.0 T and 1.5 T. T1-weighted gradient-recalled-echo (GRE) images, T2*-weighted GRE images and T2-weighted fast spin-echo (SE) images were acquired. The tumour-to-liver contrast-to-noise ratio (CNR) of the lesions was calculated. Three observers independently reviewed each image. Image artefacts and overall image quality were analysed, sensitivity and positive predictive value for the detection of hepatic metastases were calculated, and diagnostic accuracy using the receiver-operating characteristics (ROC) method was evaluated.

Results:

The tumour-to-liver CNRs were significantly higher at 3.0 T. Chemical shift and motion artefact were more severe, and overall image quality was worse on T2-weighted fast SE images at 3.0 T. Overall image quality of the two systems was similar on T1-weighted GRE images and T2*-weighted GRE images. Sensitivity and area under the ROC curve for the 3.0-T image sets were significantly higher.

Conclusion:

SPIO-enhanced MR imaging at 3.0 T provided better diagnostic performance for detection of hepatic metastases than 1.5 T.     

Axial 3D gradient-echo imaging for improved multiple sclerosis lesion detection in the cervical spinal cord at 3T

Introduction

In multiple sclerosis (MS), spinal cord imaging can help in diagnosis and follow-up evaluation. However, spinal cord magnetic resonance imaging (MRI) is technically challenging, and image quality, particularly in the axial plane, is typically poor compared to brain MRI. Because gradient-recalled echo (GRE) images might offer improved contrast resolution within the spinal cord at high magnetic field strength, both without and with a magnetization transfer prepulse, we compared them to T2-weighted fast-spin-echo (T2-FSE) images for the detection of MS lesions in the cervical cord at 3T.

Methods

On a clinical 3T MRI scanner, we studied 62 MS cases and 19 healthy volunteers. Axial 3D GRE sequences were performed without and with off-resonance radiofrequency irradiation. To mimic clinical practice, all images were evaluated in conjunction with linked images from a sagittal short tau inversion recovery scan, which is considered the gold standard for lesion detection in MS. Two experienced observers recorded image quality, location and size of focal lesions, atrophy, swelling, and diffuse signal abnormality independently at first and then in consensus.

Results

The number and volume of lesions detected with high confidence was more than three times as high on both GRE sequences compared to T2-FSE (p?<?0.0001). Approximately 5 % of GRE scans were affected by artifacts that interfered with image interpretation, not significantly different from T2W-FSE.

Conclusions

Axial 3D GRE sequences are useful for MS lesion detection when compared to 2D T2-FSE sequences in the cervical spinal cord at 3T and should be considered when examining intramedullary spinal cord lesions.     

Comparison of Gd-DTPA-induced signal enhancements in rat brain C6 glioma among different pulse sequences in 3-Tesla magnetic resonance imaging

Background: T1-shortening contrast media are routinely used in magnetic resonance (MR) examinations for the diagnosis of brain tumors. Although some studies show a benefit of 3 Tesla (T) compared to 1.5T in delineation of brain tumors using contrast media, it is unclear which pulse sequences are optimal.

Purpose: To compare gadopentetate dimeglumine (Gd-DTPA)-induced signal enhancements in rat brain C6 glioma in the thalamus region among different pulse sequences in 3T MR imaging.

Material and Methods: Five rats with a surgically implanted C6 glioma in their thalamus were examined. T1-weighted brain images of the five rats were acquired before and after Gd-DTPA administration (0.1 mmol/kg) using three clinically available pulse sequences (spin echo [SE], fast SE [FSE], fast spoiled gradient echo [FSPGR]) at 3T. Signal enhancement in the glioma (E_T) was calculated as the signal intensity after Gd-DTPA administration scaled by that before administration. Pulse sequences were compared using the Tukey-Kramer test.

Results: E_T was 1.12±0.05 for FSE, 1.26±0.11 for FSPGR, and 1.20±0.11 for SE. FSPGR showed significantly higher signal enhancement than FSE and comparable enhancement to SE.

Conclusion: FSPGR is superior to FSE and comparable to SE in its ability to delineate rat brain C6 glioma in the thalamus region.