Search

Background Simultaneous acquisition of magnetic resonance angiography (MRA) and diagnostic images is challenging in contrast-enhanced upper abdominal MRI. Purpose To evaluate the image quality of MRA of the abdomen acquired simultaneously with diagnostic MR images, and to compare the contrast effect, conspicuity of aortic branches, and pancreatic lesions in MRA between gadobutrol and gadoterate meglumine. Study type Prospective. Population Eighty-eight patients with known and suspected upper abdominal disease. Field strength/sequences 3T/4D-eTHRIVE (T1 -weighted fat-suppressed 3D fast gradient echo) for multiarterial phase imaging. Assessment The artery-to-muscle signal intensity ratio (SIR), conspicuity of aortic branches on the axial, maximum intensity projection (MIP), and volume-rendered (VR) images, and conspicuity of focal pancreatic lesions were compared between gadobutrol and gadoterate meglumine. The diameters of aortic branches were measured on axial MRA and computed tomography angiography (CTA) images and then compared. Statistical tests Quantitative and qualitative data were assessed with the Mann-Whitney U-test. The diameters of aortic branches between MRA and CTA were compared with a Spearman rank correlation test. Results View-sharing multiarterial phase imaging was successfully performed in all patients. The SIRs of common hepatic artery (P = 0.0051) and left renal artery (RA) (P = 0.045), vascular conspicuities of right and left hepatic arteries (P = 0.010 and 0.030) and right and left RAs on axial (P = 0.0065 and 0.036), and that of gastroduodenal artery on MIP (P = 0.039) with gadobutrol were significantly higher than those with gadoterate meglumine. The conspicuity of focal pancreatic lesions were comparable between the gadobutrol and gadoterate meglumine (P = 0.73). The vascular diameters on MRA and CTA were strongly correlated in all aortic branches (r = 0.842-0.942, P Data conclusion High-quality MRA of the abdomen was obtained simultaneously with the diagnostic MR images using view-sharing multiarterial phase imaging that also demonstrated comparable image quality between gadobutrol and gadoterate meglumine. Level of evidence 2 Technical Efficacy Stage 1 J. Magn. Reson. Imaging 2017.

Purpose To develop and evaluate a computer-aided diagnosis (CAD) program for liver lesions on magnetic resonance (MR) images for classification of the risk of hepatocellular carcinoma (HCC) following the liver imaging reporting and data system (LI-RADS). Materials and Methods Liver MR images from 41 patients with hyperenhancing liver lesions categorized as LR 3, 4, and 5 were evaluated by two radiologists. The major LI-RADS features of each index liver lesion were recorded, including size (maximum transverse diameter), presence of hyperenhancement, washout appearance, and capsule appearance. A CAD program was implemented to register MR images at different contrast-enhancement phases, segment liver lesions, extract lesion features, and classify lesions according to LI-RADS. The LI-RADS features quantified by CAD were compared with those assessed by radiologists using the intraclass correlation coefficient (ICC) and receiver operator curve (ROC) analyses. The LI-RADS categorization between CAD and radiologists was evaluated using the weighted Cohen's kappa coefficient. Results The mean and standard deviation of the lesion diameters were 21 ± 11 mm (range, 7–70 mm) by radiologists and 22 ± 11 mm (range, 8–72 mm) by CAD (ICC, 0.96–0.97). The area under the curve (AUC) for the washout assessment by CAD was 0.79–0.93 with sensitivity 0.69–0.82 and specificity 0.79–1. The AUC for the capsule assessment by CAD was 0.79–0.9 with sensitivity 0.75–0.9 and specificity 0.82–0.96. The classifications by the radiologists and CAD coincided in 76–83% lesions (k = 0.57–0.71), while the agreements between radiologists were in 78% lesions (k = 0.59). Conclusion We developed a CAD program for liver lesions on MR images and showed a substantial agreement in the LI-RADS-based classification of the risk of HCCs between the CAD and radiologists. Level of Evidence: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017.

PURPOSE To increase temporal-signal-to-noise ratio (tSNR) and blood oxygen level-dependent (BOLD) sensitivity at high-susceptibility regions of the brain by means of a simultaneous multiecho multithin-slice summation imaging technique. MATERIALS AND METHODS The simultaneous multislice (SMS) technique was implemented with multiecho (SMSME) and multiecho with thin-slice summation (SMSME-thin) at 3T. Multiecho data were summated based on the local apparent T2* weighting factor. Ten healthy subjects were studied for the whole brain activation by breath-holding. The tSNR values and the number of activated pixels acquired with SMSME and SMSME-thin were compared with those acquired with the conventional gradient-echo EPI in multiple brain regions RESULTS SMS methods accelerated imaging time by 5-fold as compared with the conventional method, resulting in the acquisition of three echoes and four thin-slices during the same TR of 2.5 seconds. At high-susceptibility regions, including the amygdala, inferior and middle temporal, and anterior frontal lobes, SMSME increased tSNR values by up to ∼80% and BOLD activation by up to ∼20% (paired t-test, P < 0.05). SMSME-thin further increased values as compared with SMSME (∼45% for tSNR and ∼20% for activation, P < 0.05). CONCLUSION The SMSME-thin imaging technique enhanced the temporal-signal-to-noise ratio and functional activation at high susceptibility regions of the brain. J. Magn. Reson. Imaging 2016;44:478-485.

Purpose The multiband (MB) excitation and reconstruction technique was both developed and evaluated for accelerated data acquisition of arterial spin labeling (ASL) to cover whole brain perfusion maps. Theory and Methods MB excitation was incorporated into a pulsed ASL (PASL) technique and compared with conventional single-band excitation PASL from healthy subjects, using a 32-channel head receiver coil at 3 T. The MB de-aliasing performance and effectiveness in perfusion measurement were measured with varying MB acceleration factors and gaps between MB excitations. Results The MB PASL perfusion maps were in good agreement with the conventional single-band PASL maps at matched slices. The imaging coverage could be effectively extended with the MB technique by a factor up to 5. A gap as small as 3 cm between MB excitations resulted in a comparable ASL signal loss and temporal-signal-to-noise ratio with single-band PASL. Conclusion The MB ASL technique is an effective method to evaluate whole brain perfusion because it minimizes the temporal spread of labeled spins across slices, resulting in more accurate perfusion measurements. Magn Reson Med 70:1653–1661, 2013. © 2013 Wiley Periodicals, Inc.

Compatible dual-echo arteriovenography (CODEA) is a recent MRI technique for simultaneous acquisition of an MR angiogram (MRA) and MR venogram (MRV) with image quality comparable to conventional single-echo acquisitions. The purpose of this study was to evaluate the utility of CODEA in imaging patients with chronic stroke and to test the utility of a new image representation technique (“enhanced maximum intensity projection [MIP]") based on tissue segmentation, intensity inversion, and vessel enhancement filtering) for MRV. Arterial and venous abnormalities associated with stroke were delineated on MRA and MRV acquired simultaneously with the CODEA technique. CODEA MRV displayed with the enhanced MIP technique facilitated the visualization of the overall venous structures in 3D. Reduced venous vascularity was detected in the regions of arterial occlusion compared to the contralateral normal brain regions. The CODEA technique along with the enhanced MIP technique may be valuable, particularly in clinical applications that require efficient MRA/MRV imaging because of limited scan time such as in acute stroke. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 152–156, 2013

Alternate ascending/descending directional navigation (ALADDIN) is a new imaging technique that provides interslice perfusion-weighted and magnetization transfer (MT) asymmetry images. In this article, we investigated the effects of gradient imperfections on ALADDIN MT asymmetry (MTA) signals. Subtraction artifacts increasing with readout offsets were detectable in ALADDIN MTA images from an agarose phantom but not from a water phantom. Slice-select offsets had no significant effect on the artifacts in MTA. The artifacts were suppressed by averaging signals over the readout gradient polarities independent of scan parameters. All these results suggested that the subtraction artifacts were induced by readout eddy currents. With suppression of the artifacts, ALADDIN signals in human brain and skeletal muscle varied less with scan conditions. Percent signal changes of MTA in human skeletal muscle (0.51 ± 0.11%, N = 3) were about 30% of those in white matter. The new averaging scheme will allow for more accurate MTA imaging with ALADDIN, especially at off-center positions. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

Purpose: To compare 11C-choline positron emission tomography (C-PET), 18F-fluorodeoxyglucose PET (FDG-PET), and MR imaging in the preoperative detection of prostate cancer. Materials and Methods: C-PET, FDG-PET, and MR images were obtained in 43 consecutive patients with suspected prostate cancer, and prostate cancers were histopathologically confirmed in 26 patients. Unenhanced T1-weighted, T2-weighted, and gadolinium-enhanced MR images were obtained. C-PET and FDG-PET were conducted 1.5 and 60 minutes after injection of 5.5 and 5.0 MBq/kg tracers, respectively. A nuclear and a genitourinary radiologist retrospectively reviewed PET and MR images at random, respectively, and assigned a confidence level for the presence of prostate cancer using a four-point scale. Diagnostic performance was tested using the McNemar test and receiver operating characteristic curve analysis. Results: The sensitivity was greater (P < 0.05) with MR (88%) and C-PET (73%) images than with FDG-PET images (31%). The accuracy was greater (P < 0.05) with MR images (88%) than with C-PET (67%) and FDG-PET (53%) images. The area-under-curve value with MR (0.90) was greater than those with C-PET (0.53) and FDG-PET (0.54) images (P < 0.01). Conclusion: MR imaging should be primarily performed in the preoperative detection of prostate cancer. C-PET and FDG-PET did not improve the detection. J. Magn. Reson. Imaging 2010;31:1151–1156. © 2010 Wiley-Liss, Inc.

This study evaluates reliability of current technology for measurement of renal arterial blood flow by breath-held velocity-encoded MRI. Overall accuracy was determined by comparing MRI measurements with known flow in controlled-flow-loop phantom studies. Measurements using prospective and retrospective gating methods were compared in phantom studies with pulsatile flow, not revealing significant differences. Phantom study results showed good accuracy, with deviations from true flow consistently below 13% for vessel diameters 3mm and above. Reproducibility in human subjects was evaluated by repeated studies in six healthy control subjects, comparing immediate repetition of the scan, repetition of the scan plane scouting, and week-to-week variation in repeated studies. The standard deviation in the 4-week protocol of repeated in vivo measurements of single-kidney renal flow in normal subjects was 59.7 mL/min, corresponding with an average coefficient of variation of 10.55%. Comparison of renal arterial blood flow reproducibility with and without gadolinium contrast showed no significant differences in mean or standard deviation. A breakdown among error components showed corresponding marginal standard deviations (coefficients of variation) 23.8 mL/min (4.21%) for immediate repetition of the breath-held flow scan, 39.13 mL/min (6.90%) for repeated plane scouting, and 40.76 mL/min (7.20%) for weekly fluctuations in renal blood flow.

Purpose: To implement a dual-echo sequence MRI technique at 7T for simultaneous acquisition of time-of-flight (TOF) MR angiogram (MRA) and blood oxygenation level-dependent (BOLD) MR venogram (MRV) in a single MR acquisition and to compare the image qualities with those acquired at 3T. Materials and Methods: We implemented a dual-echo sequence with an echo-specific k-space reordering scheme to uncouple the scan parameter requirements for MRA and MRV at 7T. The MRA and MRV vascular contrast was enhanced by maximally separating the k-space center regions acquired for the MRA and MRV and by adjusting and applying scan parameters compatible between the MRA and MRV. The same imaging sequence was implemented at 3T. Four normal subjects were imaged at both 3T and 7T. MRA and MRV at 7T were reconstructed both with and without phase-mask filtering and were compared quantitatively and qualitatively with those at 3T with phase-mask filtering. Results: The depiction of small cortical arteries and veins on MRA and MRV at 7T was substantially better than that at 3T, due to about twice higher contrast-to-noise ratio (CNR) for both arteries (164 ±57 vs. 77 ± 26) and veins (72 ± 8 vs. 36 ± 6). Even without use of the phase-masking filtering, the venous contrast at 7T (65 ± 7) was higher than that with the filtering at 3T (36 ± 6). Conclusion: The dual-echo arteriovenography technique we implemented at 7T allows the improved visualization of small vessels in both the MRA and MRV because of the greatly increased signal-to-noise ratio (SNR) and susceptibility contrast, compared to 3T. J. Magn. Reson. Imaging 2010;31:255–261. © 2009 Wiley-Liss, Inc.

An improved dual-echo sequence magentic resonance (MR) imaging technique was developed to simultaneously acquire a time-of-flight MR angiogram (MRA) and a blood oxygenation level-dependent MR venogram (MRV) in a single MR acquisition at 3 T. MRA and MRV require conflicting scan conditions (e.g., excitation RF profile, flip angle, and spatial presaturation pulse) for their optimal image quality. This conflict was not well counterbalanced or reconciled in previous methods reported for simultaneous acquisition of MRA and MRV. In our dual-echo sequence method, an echo-specific K-space reordering scheme was used to uncouple the scan parameter requirements for MRA and MRV. The MRA and MRV vascular contrast was enhanced by maximally separating the K-space center regions acquired for the MRA and MRV, and by adjusting and applying scan parameters compatible between the MRA and MRV. As a preliminary result, we were able to acquire a simultaneous dual-echo MRA and MRV with image quality comparable to that of the conventional single-echo MRA and MRV that were acquired separately at two different sessions. Furthermore, integrated with tilted optimized nonsaturating excitation and multiple overlapping thin-slab acquisition techniques, our dual-echo MRA and MRV provided seamless vascular continuity over a large coverage volume of the brain anatomy. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

The objective of this research was to develop and validate a custom computed tomography dose-reduction simulation technique for producing images that have an appearance consistent with the same scan performed at a lower mAs (with fixed kVp, rotation time, and collimation). Synthetic noise is added to projection (sinogram) data, incorporating a stochastic noise model that includes energy-integrating detectors, tube-current modulation, bowtie beam filtering, and electronic system noise. Experimental methods were developed to determine the parameters required for each component of the noise model. As a validation, the outputs of the simulations were compared to measurements with cadavers in the image domain and with phantoms in both the sinogram and image domain, using an unbiased root-mean-square relative error metric to quantify agreement in noise processes. Four-alternative forced-choice (4AFC) observer studies were conducted to confirm the realistic appearance of simulated noise, and the effects of various system model components on visual noise were studied. The ''just noticeable difference (JND)'' in noise levels was analyzed to determine the sensitivity of observers to changes in noise level. Individual detector measurements were shown to be normally distributed (p>0.54), justifying the use of a Gaussian random noise generator for simulations. Phantom tests showed the ability tomore » match original and simulated noise variance in the sinogram domain to within 5.6%{+-}1.6% (standard deviation), which was then propagated into the image domain with errors less than 4.1%{+-}1.6%. Cadaver measurements indicated that image noise was matched to within 2.6%{+-}2.0%. More importantly, the 4AFC observer studies indicated that the simulated images were realistic, i.e., no detectable difference between simulated and original images (p=0.86) was observed. JND studies indicated that observers' sensitivity to change in noise levels corresponded to a 25% difference in dose, which is far larger than the noise accuracy achieved by simulation. In summary, the dose-reduction simulation tool demonstrated excellent accuracy in providing realistic images. The methodology promises to be a useful tool for researchers and radiologists to explore dose reduction protocols in an effort to produce diagnostic images with radiation dose ''as low as reasonably achievable.''.« less

In ultrahigh-field MRI, such as 7 T, the signal-to-noise ratio (SNR) increases while transmit (Tx) field (B1+) can be degraded due to inhomogeneity and elevated specific absorption rate (SAR). By applying new array coil concepts to both Tx and receive (Rx) coils, the B1+ homogeneity and SNR can be improved. In this study, we developed and tested in vivo a new RF coil system for 7 T breast MRI. An RF coil system composed of an eight-channel Tx-only array based on a tic-tac-toe design (can be combined to operate in single-Tx mode) in conjunction with an eight-channel Rx-only insert was developed. Characterizations of the B1+ field and associated SAR generated by the developed RF coil system were numerically calculated and empirically measured using an anatomically detailed breast model, phantom and human breasts. In vivo comparisons between 3 T (using standard commercial solutions) and 7 T (using the newly developed coil system) breast imaging were made. At 7 T, about 20% B1+ inhomogeneity (standard deviation over the mean) was measured within the breast tissue for both the RF simulations and 7 T experiments. The addition of the Rx-only array enhances the SNR by a factor of about three. High-quality MR images of human breast were acquired in vivo at 7 T. For the in vivo comparisons between 3 T and 7 T, an approximately fourfold increase of SNR was measured with 7 T imaging. The B1+ field distributions in the breast model, phantom and in vivo were in reasonable agreement. High-quality 7 T in vivo breast MRI was successfully acquired at 0.6 mm isotropic resolution using the newly developed RF coil system.

In magnetic resonance angiography, contrast agents are frequently used to help highlight arteries over background tissue. Unfortunately, enhancing veins hamper the visualization of arteries when data are collected over a long period of time after the arterial phase of the contrast agent. To overcome this problem, we have developed a novel imaging and postprocessing method that is capable of eliminating veins by utilizing the susceptibility difference between veins and surrounding tissue. This method was applied in the peripheral vasculature where the vessels are predominantly parallel to the main field and where the blood oxygen level-dependent effect is most pronounced. Results are presented for both long (15.8 msec) and short echo times (7.8 msec) and for sequential and centrally reordered acquisition schemes. The short echo scan approach appears to be the most promising, making it possible to obtain good suppression of the venous signal even when the timing is not perfect or when repeat scans are necessary.

The impact of the contrast infusion scheme on contrast-enhanced coronary artery imaging was investigated. The imaging technique was a retrospective respiratory-gated gradient-echo sequence. To improve the contrast between blood vessels and myocardium, an inversion pulse was applied to null the myocardial signal. Extravascular contrast agent was infused slowly during data acquisition. Two contrast infusion schemes were compared in animal and volunteer studies and with simulations. One scheme enhanced blood signals during acquisition of both peripheral and central k-space data, which resulted in a relatively flat low-pass k-space filter. The other scheme mainly enhanced blood signals during acquisition of central k-space data, which resulted in a sharp low-pass k-space filter. It is concluded that the former scheme improves the signal-to-noise ratio and edge definition of coronary arteries compared with the latter scheme. J. Magn. Reson. Imaging 1999;10:800-805.

The segmentation and three-dimensional representation of the liver from a computed tomography (CT) scan is an important step in many medical applications, such as in the surgical planning for a living-donor liver transplant and in the automatic detection and documentation of pathological states. A method is being developed to automatically extract liver structure from abdominal CT scans using a priori information about liver morphology and digital image-processing techniques. Segmentation is performed sequentially image-by-image (slice-by-slice), starting with a reference image in which the liver occupies almost the entire right half of the abdomen cross section. Image processing techniques include gray-level thresholding, Gaussian smoothing, and eight-point connectivity tracking. For each case, the shape, size, and pixel density distribution of the liver are recorded for each CT image and used in the processing of other CT images. Extracted boundaries of the liver are smoothed using mathematical morphology techniques and B-splines. Computer-determined boundaries were compared with those drawn by a radiologist. The boundary descriptions from the two methods were in agreement, and the calculated areas were within 10%.

Purpose: To develop a fully automated method to segment cartilage from the magnetic resonance (MR) images of knee and to evaluate the performance of the method on a public, open dataset. Methods: The segmentation scheme consisted of three procedures: multiple-atlas building, applying a locally weighted vote (LWV), and region adjustment. In the atlas building procedure, all training cases were registered to a target image by a nonrigid registration scheme and the best matched atlases selected. A LWV algorithm was applied to merge the information from these atlases and generate the initial segmentation result. Subsequently, for the region adjustment procedure, the statistical information of bone, cartilage, and surrounding regions was computed from the initial segmentation result. The statistical information directed the automated determination of the seed points inside and outside bone regions for the graph-cut based method. Finally, the region adjustment was conducted by the revision of outliers and the inclusion of abnormal bone regions. Results: A total of 150 knee MR images from a public, open dataset (available atwww.ski10.org) were used for the development and evaluation of this approach. The 150 cases were divided into the training set (100 cases) and the test set (50 cases). The cartilages were segmented successfully in all test cases in an average of 40 min computation time. The average dice similarity coefficient was 71.7% ± 8.0% for femoral and 72.4% ± 6.9% for tibial cartilage. Conclusions: The authors have developed a fully automated segmentation program for knee cartilage from MR images. The performance of the program based on 50 test cases was highly promising.

Purpose: To develop and validate a CTdose reduction simulation model. Method and Materials: A noise model was developed incorporating the mechanisms of stochastic noise in energy‐integrating x‐ray detectors, tube current modulation, bowtie beam filtering, and electronic system noise by adding synthetic noise to projection data (sinogram).Experiments were performed to determine the parameters required for the noise model, and the effects of various components were studied. Various scans were performed on an empty gantry, cylinder phantom, cadaver head, and a skull (an asymmetric object) at varyious flux levels. Seventeen clinical scans from three different centers were included. As a validation, the outputs of the simulations were compared to actual measurements in both the sinogram and image domain. Four‐alternative forced‐choice (4AFC) observer studies were performed to confirm the realistic appearance of simulated images. Tests were conducted to establish the “just noticeable difference (JND)” in noise levels, and the sensitivities of observers to changes in noise levels were determined. Results: The gaussian random noise generator was found to be appropriate for simulations. Measurements demonstrated a match of the noise variance to within 5% in the sinogram domain, which propagates into the image domain. The 4AFC observer studies indicated that the simulated imagery was realistic, with no detectable difference between simulated and original imagery (25%±7.9%). The JND studies indicated that observers reliably detected noise‐levels differences corresponding to 20–30% changes in tube current, implying that accuracies in simulation on the order of ∼9% would result in images that could not be reliably differentiated from original images.Conclusion: The dose‐reduction simulation tool demonstrated excellent image fidelity. The methodology promises to be a useful tool for radiologists to explore dose reduction protocols in efforts to produce diagnostic images with radiation dose “as low as reasonably achievable” (ALARA).

Purpose: Generally, in MRI, PET, and CTimage datasets, more information is available for defining the target volume (or normal structures) than is used during the target segmentation. We introduce a method to take advantage of all the imaging information available for target segmentation, including multi‐modality images or multiple image sets from the same modality. Method and Materials: We generalized the multi‐valued level set deformable model (Chan et al., JVCI (2000) 11:130–141) for simultaneous 2D/3D segmentation/registration of multi‐modality images consisting of a combination of PET, CT, or MR datasets. Information from multi modality image sets is combined to define the final target volume. The method was evaluated on three patient cases, including: a non‐small cell lungcancer case with PET/CT, a cervix cancer case with PET/CT, and a prostate patient case with CT and MR. Results: In the case of the lungtumor the level set algorithm took 120 iterations for convergence, while in the case cervix tumor it converged after 30 iterations because the tumor has a deformed circular shape. In the prostate case, it took 50 iterations to converge and the results were made more sensitive to the shape prior information, because MR provides less gradient strength than PET. The computational time was on the order of few seconds in all cases. Conclusion: We a developed a new target segmentation algorithm which uses information simultaneously from multiple modalities. Our initial results indicate that the algorithm is promising and could provide physicians with a reliable contouring tool for lung, cervical, and prostate cancer. This research was partially supported by NIH grant R01 CA85181 and a grant from TomoTherapy, Inc.