Radiology Technical Developments

[Technical Developments] Liver Imaging at 3.0 T: Diffusion-induced Black-Blood Echo-planar Imaging with Large Anatomic Volumetric Coverage as an Alternative for Specific Absorption Rate-intensive Echo-Train Spin-Echo Sequences: Feasibility Study

van den Bos, I. C., Hussain, S. M., Krestin, G. P., Wielopolski, P. A. — 2008-06-19

Institutional Review Board approval and signed informed consent were obtained by all participants for an ongoing sequence optimization project at 3.0 T. The purpose of this study was to evaluate breath-hold diffusion-induced black-blood echo-planar imaging (BBEPI) as a potential alternative for specific absorption rate (SAR)-intensive spin-echo sequences, in particular, the fast spin-echo (FSE) sequences, at 3.0 T. Fourteen healthy volunteers (seven men, seven women; mean age ± standard deviation, 32.7 years ± 6.8) were imaged for this purpose. Liver coverage (20 cm, z-axis) was always performed in one 25-second breath hold. Imaging parameters were varied interactively with regard to echo time, diffusion b value, and voxel size. Images were evaluated and compared with fat-suppressed T2-weighted FSE images for image quality, liver delineation, geometric distortions, fat suppression, suppression of the blood signal, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR). An optimized short- (25 msec) and long-echo (80 msec) BBEPI provided full anatomic, single breath-hold liver coverage (100 and 50 sections, respectively), with resulting voxel sizes of 3.3 x 2.7 x 2.0 mm and 3.3 x 2.7 x 4.0 mm, respectively. Repetition time was 6300 msec, matrix size was 160 x 192, and an acceleration factor of 2.00 was used. b Values of more than 20 sec/mm² showed better suppression of the blood signal but b values of 10 sec/mm² provided improved volume coverage and signal consistency. Compared with fat-suppressed T2-weighted FSE, the optimized BBEPI sequence provided (a) comparable image quality and liver delineation, (b) acceptable geometric distortions, (c) improved suppression of fat and blood signals, and (d) high CNR and SNR. BBEPI is feasible for fast, low-SAR, thin-section morphologic imaging of the entire liver in a single breath hold at 3.0 T.

[Technical Developments] Cerebral Microbleeds: Accelerated 3D T2-weighted GRE MR Imaging versus Conventional 2D T2-weighted GRE MR Imaging for Detection

2008-06-19

The purpose of this study was to prospectively compare high-spatial-resolution accelerated three-dimensional (3D) T2*-weighted gradient-recalled-echo (GRE) magnetic resonance (MR) images with conventional two-dimensional (2D) T2*-weighted GRE MR images for the depiction of cerebral microbleeds. After obtaining institutional review board approval and informed consent, 200 elderly participants (age range, 69.7–96.7 years; 108 [54%] women) were imaged at 1.5 T by using both sequences. Presence, number, and location of microbleeds were recorded for both sequences, and differences were tested by using McNemar and signed rank tests. Cerebral microbleeds were detected in significantly more participants on 3D T2*-weighted GRE images (35.5%) than on 2D T2*-weighted GRE images (21.0%; P < .001). Furthermore, in persons with microbleeds visualized on both image sets, significantly more microbleeds (P < .001) were seen on 3D images than on 2D images. For both sequences, the proportion of participants with a microbleed in a lobar (cortical gray and subcortical white matter), deep, or infratentorial location was similar. In conclusion, accelerated 3D T2*-weighted GRE images depict more microbleeds than do conventional 2D T2*-weighted GRE images.

[Technical Developments] Cerebral Arteries: Fully Automated Segmentation from CT Angiography--A Feasibility Study

Manniesing, R., Viergever, M. A., van der Lugt, A., Niessen, W. J. — 2008-05-16

The purpose of this study was to retrospectively assess the feasibility of a fully automated image postprocessing tool for the segmentation of the arterial cerebrovasculature from computed tomographic (CT) angiography in 27 patients (nine men, 18 women; mean age, 55 years; age range, 33–76 years) with subarachnoid hemorrhage. The institutional review board approved this study, and informed consent was waived. The proposed method, which does not require the acquisition of an additional CT scan for bone suppression, consists of the following: (a) automatic detection of the main arteries for initialization, (b) segmentation of these arteries through the skull base, and (c) suppression of the large veins near the skull. The parameters of this method were optimized on the training subset of nine patients, and the method was successful at segmentation of the arteries in 15 (83%) of the 18 remaining patients. The difference between automatic and manual diameter measurements was 0.0 mm ± 0.4 (standard deviation). The study results showed that fully automated segmentation of the cerebral arteries is feasible.

Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/247/3/841/DC1

[Technical Developments] Real-time MR-guided Wire Localization of Breast Lesions by Using an Open 1.0-T Imager: Initial Experience

2008-04-22

The purpose of this study was to prospectively evaluate technique and time factors for real-time magnetic resonance (MR) imaging–guided wire localization of suspicious breast lesions by using an open 1.0-T MR imager. It was conducted with institutional review board approval; informed consent was given by patients. Needle placement was monitored in 30 women (mean age, 50.5 years; range, 28–70 years) by using a dynamic balanced gradient-echo (single-shot turbo field-echo [TFE]) sequence with a temporal resolution of 0.5 second. In all patients, the tip of the needle was clearly identified during placement. Consistent with balanced TFE (BTFE) imaging, diagnostic MR imaging after the interventional procedure confirmed that the hookwires were placed 0–6 mm (mean, 3.3 mm) from the target lesions. The total procedure time ranged from 16–36 minutes. Results show that real-time MR-guided wire localization permits correction of the needle position during placement and reduces the interventional procedure time.

Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/2472071039/DC1

[Technical Developments] Transperineal Prostate Intervention: Robot for Fully Automated MR Imaging--System Description and Proof of Principle in a Canine Model

2008-04-22

The study was approved by the animal care and use committee. The purpose of the study was to prospectively establish proof of principle in vivo in canines for a magnetic resonance (MR) imaging–compatible robotic system designed for image-guided prostatic needle intervention. The entire robot is built with nonmagnetic and dielectric materials and in its current configuration is designed to perform fully automated brachytherapy seed placement within a closed MR imager. With a 3.0-T imager, in four dogs the median error for MR imaging–guided needle positioning and seed positioning was 2.02 mm (range, 0.86–3.18 mm) and 2.50 mm (range, 1.45–10.54 mm), respectively. The robotic system is capable of accurate MR imaging–guided prostatic needle intervention within a standard MR imager in vivo in a canine model.

[Technical Developments] Liver Fat Content and T2*: Simultaneous Measurement by Using Breath-hold Multiecho MR Imaging at 3.0 T--Feasibility

2008-04-22

Research ethics committee approval was obtained for this study, and written informed consent was obtained from all participants. The purpose was to prospectively evaluate the feasibility of breath-hold multiecho in- and out-of-phase magnetic resonance (MR) imaging for simultaneous lipid quantification and T2* measurement. A spoiled gradient-echo sequence with seven echo times alternately in phase and out of phase was used at 3.0 T. Imaging was performed in a lipid phantom, in five healthy volunteers (all men; mean age, 37 years), and in five obese individuals with hyperlipidemia or diabetes (four men, one woman; mean age, 53 years). A biexponential curve-fitting model was used to derive the relative signal contributions from fat and water, and these results were compared with results of liver proton MR spectroscopy, the reference standard. There was a significant correlation between multiecho and spectroscopic measurements of hepatic lipid concentration (r² = 0.99, P < .001). In vivo, the T2* of water was consistently longer than that of fat and reliably enabled the signal components to be correctly assigned. In the lipid phantom, the multiecho method could be used to determine the fat-to-water ratio and the T2* values of fat and water throughout the entire range of fat concentrations. Multiecho imaging shows promise as a method of simultaneous fat and T2* quantification.

[Technical Developments] Coronary Artery Anomalies and Variants: Technical Feasibility of Assessment with Coronary MR Angiography at 3 T

2008-03-27

The purpose of this study was to prospectively use a whole-heart three-dimensional (3D) coronary magnetic resonance (MR) angiography technique specifically adapted for use at 3 T and a parallel imaging technique (sensitivity encoding) to evaluate coronary arterial anomalies and variants (CAAV). This HIPAA-compliant study was approved by the local institutional review board, and informed consent was obtained from all participants. Twenty-two participants (11 men, 11 women; age range, 18–62 years) were included. Ten participants were healthy volunteers, whereas 12 participants were patients suspected of having CAAV. Coronary MR angiography was performed with a 3-T MR imager. A 3D free-breathing navigator-gated and vector electrocardiographically–gated segmented k-space gradient-echo sequence with adiabatic T2 preparation pulse and parallel imaging (sensitivity encoding) was used. Whole-heart acquisitions (repetition time msec/echo time msec, 4/1.35; 20° flip angle; 1 x 1 x 2-mm acquired voxel size) lasted 10–12 minutes. Mean examination time was 41 minutes ± 14 (standard deviation). Findings included aneurysms, ectasia, arteriovenous fistulas, and anomalous origins. The 3D whole-heart acquisitions developed for use with 3 T are feasible for use in the assessment of CAAV.

[Technical Developments] Isotropic High-Spatial-Resolution Contrast-enhanced 3.0-T MR Angiography in Patients Suspected of Having Renal Artery Stenosis

2008-03-27

The purpose of this study was to prospectively evaluate the diagnostic performance of contrast material–enhanced magnetic resonance (MR) angiography performed at 3 T for assessment of renal artery stenosis (RAS) by using parallel acquisition techniques with high acceleration factors and with digital subtraction angiography (DSA) as the reference standard. The study was institutional review board approved, and written informed consent was obtained from all patients. Twenty-nine patients (18 men, 11 women; mean age, 57.1 years ± 14.3 [standard deviation]) suspected of having RAS underwent MR angiography. Images were evaluated qualitatively and quantitatively. The interobserver variability, sensitivity, specificity, and positive and negative predictive values of 3-T MR angiography, as compared with DSA (performed in 15 patients), were calculated. All examinations yielded good or excellent image quality. The sensitivity and specificity of MR angiography in grading significant (>75%) stenosis were 94% and 96%, respectively. Owing to its high sensitivity, contrast-enhanced 3-T MR angiography can be used reliably to exclude RAS and can serve as a useful screening method in the diagnostic work-up of patients with arterial hypertension.

[Technical Developments] Semiautomated Quantification of the Mass and Distribution of Vascular Calcification with Multidetector CT: Method and Evaluation

Raman, R., Raman, B., Napel, S., Rubin, G. D. — 2008-03-27

Institutional review board approval was obtained for this HIPAA-compliant study. Informed consent was obtained for prospective evaluation in 21 asymptomatic volunteers (10 women, 11 men; mean age, 60 years) but waived for retrospective (10 patients with and five patients without disease) evaluation. Prospective validation was in phantoms. Quantification of mass and calcium distribution was performed with fast semiautomated method, without calibration. For actual versus measured mass in phantoms, R² was 0.98; absolute and percentage errors were 1.2 mg and 9.1%, respectively. In asymptomatic volunteers, mean interscan variability for calcium mass quantification in extracoronary arteries was 24.9 mg; mean was 991 units for Agatston scoring. In coronary arteries, mean variability was 5.5 mg; mean Agatston variability was 27.7 units. At retrospective computed tomography, mean total calcified mass was 321.3 mg. Accurate quantification of mass and distribution of calcification in simulated arteries with this method can be applied in vivo, with low interscan variability.

Radiology Technical Developments

[Technical Developments] Liver Imaging at 3.0 T: Diffusion-induced Black-Blood Echo-planar Imaging with Large Anatomic Volumetric Coverage as an Alternative for Specific Absorption Rate-intensive Echo-Train Spin-Echo Sequences: Feasibility Study

[Technical Developments] Cerebral Microbleeds: Accelerated 3D T2*-weighted GRE MR Imaging versus Conventional 2D T2*-weighted GRE MR Imaging for Detection

[Technical Developments] Cerebral Arteries: Fully Automated Segmentation from CT Angiography--A Feasibility Study

[Technical Developments] Real-time MR-guided Wire Localization of Breast Lesions by Using an Open 1.0-T Imager: Initial Experience

[Technical Developments] Transperineal Prostate Intervention: Robot for Fully Automated MR Imaging--System Description and Proof of Principle in a Canine Model

[Technical Developments] Liver Fat Content and T2*: Simultaneous Measurement by Using Breath-hold Multiecho MR Imaging at 3.0 T--Feasibility

[Technical Developments] Coronary Artery Anomalies and Variants: Technical Feasibility of Assessment with Coronary MR Angiography at 3 T

[Technical Developments] Isotropic High-Spatial-Resolution Contrast-enhanced 3.0-T MR Angiography in Patients Suspected of Having Renal Artery Stenosis

[Technical Developments] Semiautomated Quantification of the Mass and Distribution of Vascular Calcification with Multidetector CT: Method and Evaluation

[Technical Developments] Cerebral Microbleeds: Accelerated 3D T2-weighted GRE MR Imaging versus Conventional 2D T2-weighted GRE MR Imaging for Detection