Radiology Technical Developments

[Technical Developments] Left Ventricle: Automated Segmentation by Using Myocardial Effusion Threshold Reduction and Intravoxel Computation at MR Imaging

2008-08-18

This retrospective analysis of existing patient data had institutional review board approval and was performed in compliance with HIPAA. No informed consent was required. The purpose of the study was to develop and validate an algorithm for automated segmentation of the left ventricular (LV) cavity that accounts for papillary and/or trabecular muscles and partial voxels in cine magnetic resonance (MR) images, an algorithm called LV Myocardial Effusion Threshold Reduction with Intravoxel Computation (LV-METRIC). The algorithm was validated in biologic phantoms, and its results were compared with those of manual tracing, as well as those of a commercial automated segmentation software (MASS [MR Analytical Software System]), in 38 subjects. LV-METRIC accuracy in vitro was 98.7%. Among the 38 subjects studied, LV-METRIC and MASS ejection fraction estimations were highly correlated with manual tracing (R² = 0.97 and R² = 0.95, respectively). Ventricular volume estimations were smaller with LV-METRIC and larger with MASS than those calculated by using manual tracing, though all results were well correlated (R² = 0.99). LV-METRIC volume measurements without partial voxel interpolation were statistically equivalent to manual tracing results (P > .05). LV-METRIC had reduced intraobserver and interobserver variability compared with other methods. MASS required additional manual intervention in 58% of cases, whereas LV-METRIC required no additional corrections. LV-METRIC reliably and reproducibly measured LV volumes.

Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/248/3/1004/DC1

[Technical Developments] Modulation Transfer Function-based Assessment of Temporal Resolution: Validation for Single- and Dual-Source CT

Ertel, D., Krober, E., Kyriakou, Y., Langner, O., Kalender, W. A. — 2008-08-18

The purpose of this study was to determine a manufacturer-independent quality assurance measurement for temporal resolution with a three-dimensional cardiac motion robot; validation was with single-source (SS) and dual-source (DS) computed tomography (CT). Image acquisition was performed by using standard cardiac protocols. Image contrast–based modulation transfer function (MTF) was assessed as function of time. For motion frequency of 60 beats per minute, MTF slightly decreased by 14% and 6% for SS CT and DS CT, respectively. For higher frequencies, a stronger decrease of MTF (eg, by 50% [SS CT] and 18% [DS CT] at 120 beats per minute) was detected. Effect of manufacturer's adaptive bisegment algorithm for SS CT and corresponding resonance effects of rotation time and heart rate were quantified. The robot-based approach is a reproducible, objective way to assess temporal resolution; it allows practical measurement of temporal resolution and comparison of CT scanners and protocols.

[Technical Developments] Volume Rendering with Color Coding of Tagged Stool during Endoluminal Fly-through CT Colonography: Effect on Reading Efficiency

2008-08-18

Institutional review board approval and informed consent were obtained. This study was conducted to evaluate a newly developed technique for discriminative color coding of tagged stool during three-dimensional (3D) endoluminal fly-through computed tomographic (CT) colonography and to determine its effect on reading efficiency. Thirty patients, including three dropouts, were prepared with moderate cathartic preparation (20 mg bisacodyl, three doses of 200 mL of 5% wt/vol barium sulfate). Images were reviewed by two independent readers with and without color coding. Reader preference, interpretation time, and diagnostic performance were evaluated. Both reviewers preferred color coding. With color coding, interpretation time was shortened by 3 minutes (reader 1, P = .002) and 2.5 minutes (reader 2, P = .009); sensitivity for 6-mm-diameter or larger lesions remained constant at 96% (24 of 25; 95% confidence interval: 78.9%, <100%; P = >.99). This technique facilitates primary 3D interpretation of images obtained with moderate cathartic preparation.

[Technical Developments] Simultaneous MR/PET Imaging of the Human Brain: Feasibility Study

2008-08-18

The purpose of this study was to apply a magnetic resonance (MR) imaging–compatible positron emission tomographic (PET) detector technology for simultaneous MR/PET imaging of the human brain and skull base. The PET detector ring consists of lutetium oxyorthosilicate (LSO) scintillation crystals in combination with avalanche photodiodes (APDs) mounted in a clinical 3-T MR imager with use of the birdcage transmit/receive head coil. Following phantom studies, two patients were simultaneously examined by using fluorine 18 fluorodeoxyglucose (FDG) PET and MR imaging and spectroscopy. MR/PET data enabled accurate coregistration of morphologic and multifunctional information. Simultaneous MR/PET imaging is feasible in humans, opening up new possibilities for the emerging field of molecular imaging.

[Technical Developments] Volumetric Cardiac Quantification by Using 3D Dual-Phase Whole-Heart MR Imaging

2008-07-18

This study was approved by the local institutional ethics committee, and informed consent was obtained from all volunteers and patients. The purpose of the study was to assess ventricular volumes by using three-dimensional (3D) whole-heart data sets acquired during end-systolic and end-diastolic phases during one free-breathing magnetic resonance imaging examination. In five healthy volunteers and 10 patients, 3D dual cardiac phase data sets, short-axis multisection breath-hold images, and through-plane flow images of the great vessels were acquired. Within these data sets, statistic analyses were performed to compare stroke, end-systolic, and end-diastolic volumes for the left ventricle (LV) and the right ventricle (RV). Results showed that the breath-hold multisection approach, the flow measurement approach, and the new dual-phase 3D approach delivered comparable results for quantification of cardiac volumes and function. High correlation values greater than 0.95 were found when these methods were compared, and no significant differences were recognized for stroke, end-systolic, or end-diastolic volumes in either the LV or the RV.

[Technical Developments] Xenon Ventilation CT with a Dual-Energy Technique of Dual-Source CT: Initial Experience

2008-07-18

Institutional review board approval and written informed consent were obtained. Although xenon (Xe) ventilation CT has been introduced as a potential method with which to depict regional ventilation, quantification of Xe enhancement has been limited by the variability of lung attenuation caused by different lung volumes between scans. The purpose of this study was to assess the feasibility of Xe ventilation CT with a dual-energy technique. Dual-energy CT was performed in 12 subjects after Xe inhalation. With use of a dual-energy technique, the Xe component could be extracted without any influence from lung volume. Dynamic and static regional ventilation function can be displayed with an exact match to the thin-section CT image.

Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/248/2/615/DC1

[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

Radiology Technical Developments

[Technical Developments] Left Ventricle: Automated Segmentation by Using Myocardial Effusion Threshold Reduction and Intravoxel Computation at MR Imaging

[Technical Developments] Modulation Transfer Function-based Assessment of Temporal Resolution: Validation for Single- and Dual-Source CT

[Technical Developments] Volume Rendering with Color Coding of Tagged Stool during Endoluminal Fly-through CT Colonography: Effect on Reading Efficiency

[Technical Developments] Simultaneous MR/PET Imaging of the Human Brain: Feasibility Study

[Technical Developments] Volumetric Cardiac Quantification by Using 3D Dual-Phase Whole-Heart MR Imaging

[Technical Developments] Xenon Ventilation CT with a Dual-Energy Technique of Dual-Source CT: Initial Experience

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