Enhancement in a brain glioma model: a comparison of half-dose gadobenate dimeglumine versus full-dose gadopentetate dimeglumine at 1.5 and 3 T.

PURPOSE: To examine dose reduction comparing enhancement with full-dose gadopentetate dimeglumine (0.1 mmol/kg) to half-dose gadobenate dimeglumine in a rat brain glioma model. MATERIALS AND METHODS: Intra-axial parenchymal brain tumors were implanted in 17 experimental animals. The 13 surviving animals were imaged at 1.5 or 3 T. Either gadopentetate dimeglumine or gadobenate dimeglumine was injected in random order on consecutive days. Tumor signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and contrast enhancement (CE) for each agent were obtained with region of interest analyses and compared. Lesions were confirmed histopathologically. RESULTS: Statistically significantly lower SNR, CNR, and CE parameters were found at both 1.5 and 3 T with half-dose gadobenate dimeglumine relative to full-dose gadopentetate dimeglumine (P < 0.05). SNR on average at 3 T was 70.0 ± 14.4 for gadopentetate dimeglumine and 57.0 0 ± 4.8 for gadobenate dimeglumine (P < 0.02). CONCLUSION: Improved r1 relaxivity with gadobenate dimeglumine does not produce adequate half-dose contrast-enhancement relative to full-dose gadopentetate dimeglumine.

Technical considerations in MR angiography: an image-based guide.

As the complexity of the magnetic resonance angiography (MRA) techniques grows, it becomes more difficult for the practicing radiologist to appreciate the physical principles underlying these studies. Nevertheless, such an understanding is requisite for improving clinical image quality. As radiologists are most accustomed to dealing with medical images in everyday practice, it seems natural that an image-based approach to teaching MRA physics, rather than complex mathematical equations or pulse sequence diagrams, would be preferable. This article adopts such an approach. Simple ways to improve MRA image quality are emphasized along with new technologies and their physical basis. The ultimate goal of the article is to facilitate the practicing radiologist becoming more aware of the variety of MR techniques available, being more confident in modifying sequence parameters to improve image quality and reduce contrast dose, and understanding the basis behind newer MRA techniques.

Clinical evaluation of single-shot and readout-segmented diffusion-weighted imaging in stroke patients at 3 T.

BACKGROUND: Diffusion-weighted imaging (DWI) magnetic resonance imaging (MRI) is most commonly performed utilizing a single-shot echo-planar imaging technique (ss-EPI). Susceptibility artifact and image blur are severe when this sequence is utilized at 3 T. PURPOSE: To evaluate a readout-segmented approach to DWI MR in comparison with single-shot echo planar imaging for brain MRI. MATERIAL AND METHODS: Eleven healthy volunteers and 14 patients with acute and early subacute infarctions underwent DWI MR examinations at 1.5 and 3T with ss-EPI and readout-segmented echo-planar (rs-EPI) DWI at equal nominal spatial resolutions. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) calculations were made, and two blinded readers ranked the scans in terms of high signal intensity bulk susceptibility artifact, spatial distortions, image blur, overall preference, and motion artifact. RESULTS: SNR and CNR were greatest with rs-EPI (8.1 ± 0.2 SNR vs. 6.0 ± 0.2; P <10(-4) at 3T). Spatial distortions were greater with single-shot (0.23 ± 0.03 at 3T; P <0.001) than with rs-EPI (0.12 ± 0.02 at 3T). Combined with blur and artifact reduction, this resulted in a qualitative preference for the readout-segmented scans overall. CONCLUSION: Substantial image quality improvements are possible with readout-segmented vs. single-shot EPI - the current clinical standard for DWI - regardless of field strength (1.5 or 3 T). This results in improved image quality secondary to greater real spatial resolution and reduced artifacts from susceptibility in MR imaging of the brain.

Echo planar diffusion-weighted imaging: possibilities and considerations with 12- and 32-channel head coils.

Interest in clinical brain magnetic resonance imaging using 32-channel head coils for signal reception continues to increase. The present investigation assesses possibilities for improving diffusion-weighted image quality using a 32-channel in comparison to a conventional 12-channel coil. The utility of single-shot (ss) and an approach to readout-segmented (rs) echo planar imaging (EPI) are examined using both head coils. Substantial image quality improvements are found with rs-EPI. Imaging with a 32-channel head coil allows for implementation of greater parallel imaging acceleration factors or acquisition of scans at a higher resolution. Specifically, higher resolution imaging with rs-EPI can be achieved by increasing the number of readout segments without increasing echo-spacing or echo time to the degree necessary with ss-EPI - a factor resulting in increased susceptibility artifact and reduced signal-to-noise with the latter.

Time-resolved MR angiography of renal artery stenosis in a swine model at 3 Tesla using gadobutrol with digital subtraction angiography correlation.

PURPOSE: To establish the minimum dose required for detection of renal artery stenosis using high temporal resolution, contrast enhanced MR angiography (MRA) in a porcine model. MATERIALS AND METHODS: Surgically created renal artery stenoses were imaged with 3 Tesla MR and digital subtraction angiography (DSA) in 12 swine in this IACUC approved protocol. Gadobutrol was injected intravenously at doses of 0.5, 1, 2, and 4 mL for time-resolved MRA (1.5 × 1.5 mm(2) spatial resolution). Region of interest analysis was performed together with stenosis assessment and qualitative evaluation by two blinded readers. RESULTS: Mean signal to noise ratio (SNR) and contrast to noise ratio (CNR) values were statistically significantly less with the 0.5-mL protocol (P < 0.001). There were no statistically significant differences among the other evaluated doses. Both readers found 10/12 cases with the 0.5-mL protocol to be of inadequate diagnostic quality (κ = 1.0). All other scans were found to be adequate for diagnosis. Accuracies in distinguishing between mild/insignificant (<50%) and higher grade stenoses (>50%) were comparable among the higher-dose protocols (sensitivities 73-93%, specificities 62-100%). CONCLUSION: Renal artery stenosis can be assessed with very low doses (~0.025 mmol/kg bodyweight) of a high concentration, high relaxivity gadolinium chelate formulation in a swine model, results which are promising with respect to limiting exposure to gadolinium based contrast agents.

Are you ready?--lessons learned from the Fort Hood shooting in Texas.

On November 5, 2009, a US Army psychiatrist allegedly opened fire with one or more handguns, killing 12 military personnel and one civilian at Fort Hood in Killeen, Texas. The most severely wounded casualties were transported to Scott and White Memorial Hospital, a Level I trauma center and tertiary care teaching hospital in Temple, Texas associated with the Texas A&M University College of Medicine. Ten victims arrived in a 1-h period with another two arriving in the second hour, necessitating an emergency response to a mass casualty event. Our radiology department's response was largely unplanned and was therefore the result of many spontaneous actions and ideas. We share our experiences and from them formulate guidelines for a general radiology surge model for mass casualty events. It is our hope to raise awareness and help other radiology departments to prepare for such an unexpected event.

IDEAL imaging of the musculoskeletal system: robust water fat separation for uniform fat suppression, marrow evaluation, and cartilage imaging.

OBJECTIVE: The objective of this article is to discuss the acquisition of high-quality MR images of the musculoskeletal system with uniform fat suppression using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL). IDEAL is a three-point water-fat separation method that provides robust fat suppression even in the complex magnetic environments commonly encountered during clinical musculoskeletal imaging. CONCLUSION: The IDEAL technique provides uniform fat saturation even in complex magnetic environments and simultaneously produces in-phase and opposed-phase images that may be useful for characterization of osseous lesions. The IDEAL water-fat separation method is highly versatile and has been successfully combined with T1-weighted, T2-weighted, steady-state free precession, and spoiled gradient-recalled echo techniques to produce high-quality MR images in clinically acceptable scanning times.