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BACKGROUND Contrast bolus variation during contrast-enhanced magnetic resonance angiography (CE-MRA) acquisition may lead to vessel blurring. PURPOSE To combine knowledge of how contrast signal intensity (SI) evolves for different injection strategies with anatomically familiar parametric computer models to measure and visually assess the effects of a wide range of variables on modeled CE-MRA, and in doing so develop contrast rate injection guidelines. STUDY TYPE Computer modeling. PHANTOM Digital three-dimensional phantom consisting of orthogonal "aorta," 7 mm diameter "renal arteries" (with 57% and 86% diameter stenoses), and 7 mm diameter "superior mesenteric artery" (with 57% diameter stenosis). FIELD STRENGTH/SEQUENCE One millimeter in-plane resolution arterial CE-MRA imaging at 3 T. ASSESSMENT "Background" (time invariant) and "vascular" (time varying) components of the phantom were each Fourier transformed into the spatial frequency domain, the latter modulated by the SI evolution of a contrast bolus of varying "plateau" lengths and "tail" heights. Data are presented as surface plots of stenosis measurement error and blurring vs. a reference-standard injection. STATISTICAL TESTS Descriptive. RESULTS Shorter plateau lengths and lower tail heights resulted in increased measured stenosis error and blurring vs. the reference standard. Under a 44-second acquisition, full width half maximum stenosis error of the 86% stenosis with 25% plateau length and 25% tail height is 24% as compared to that from the reference standard. As plateau length and tail height approach 100%, stenosis error and blurring approach a floor defined by the MR acquisition's limitations. DATA CONCLUSION We propose that to achieve minimal degradation with CE-MRA, one can create a contrast bolus with either 60% plateau and 50% tail height or 80% plateau with any tail. These considerations may well prove to be of practical importance, possibly via manipulating the tail by means of multiphasic contrast injections. LEVEL OF EVIDENCE 3 TECHNICAL EFFICACY: Stage 1.

3D printing facilitates the creation of accurate physical models of patient-specific anatomy from medical imaging datasets. While the majority of models to date are created from computed tomography (CT) data, there is increasing interest in creating models from other datasets, such as ultrasound and magnetic resonance imaging (MRI). MRI, in particular, holds great potential for 3D printing, given its excellent tissue characterization and lack of ionizing radiation. There are, however, challenges to 3D printing from MRI data as well. Here we review the basics of 3D printing, explore the current strengths and weaknesses of printing from MRI data as they pertain to model accuracy, and discuss considerations in the design of MRI sequences for 3D printing. Finally, we explore the future of 3D printing and MRI, including creative applications and new materials. Level of Evidence: 5 J. Magn. Reson. Imaging 2016.

PURPOSE To evaluate a contrast agent injection method that provides constant magnetic resonance imaging (MRI) signal intensity throughout a contrast-enhanced MR angiography acquisition. MATERIALS AND METHODS A tailored injection profile (TIP) algorithm was developed that used the signal intensity profile from a test bolus as an impulse response function, and predicted the response to various multiphasic injection profiles. Antecubital vein injections were administered via a commercially available multiphasic power injector. The TIP algorithm evaluated the predicted responses and selected the injection that best matched the desired (20-sec plateau) profile. Resulting signal intensity profiles from tailored and standard injection profiles were compared in 20 subjects (10 each). All subjects received a weight-based single-dose (0.1 mmol/kg) of gadoteridol, and abdominal aorta signal intensities were measured at 3T with a time-resolved, thick-slice, 3D spoiled-gradient-echo MR sequence with parameters approximating contrast-enhanced MR angiography. The single-phase, standard injection was injected at 1.6 mL/sec. RESULTS Full-width at 80% maximum (FW80M) signal intensity was significantly longer for the tailored injection profiles (23.0 ± 2.2 vs. 9.0 ± 4.2 sec; P < 0.01). Concurrently, the profile peak signal intensity was reduced by 19% for the tailored profiles (12.0 ± 3.1 vs. 14.8 ± 2.8 times baseline; P = 0.058), nearly reaching significance. CONCLUSION Multiphasic tailored injections from a power injector produced longer signal intensity profiles (156% increase in FW80M) with an accompanying decrease (19%) in peak signal intensity compared to a standard, single-phase injection. J. Magn. Reson. Imaging 2016. J. Magn. Reson. Imaging 2016;44:1664-1672.

Purpose To develop a timing algorithm for three-station moving-table MR angiography of the peripheral arteries (pMRA) based on individual patient hemodynamics that optimizes arterial opacification and minimizes venous enhancement. Methods Two separate patient cohorts were identified for this retrospective study. The first consisted of 71 patients for development of a patient specific timing algorithm to calculate multiple contrast agent bolus transit times at 1.5 Tesla using a spoiled gradient echo sequence. This timing data was applied to a separate group of 59 patients in which one of four predetermined pMRA protocols was performed based on a time-resolved MRA of the calves. Image quality was evaluated by two blinded readers grading venous enhancement and arterial opacification. Results Transit time from abdominal aorta to foot (Ao-F) ranged from 5–46 s, with a mean of 17.8 ± 8.2 s. Arteriovenous window (AVW) transit time ranged from −5 to 65 s, with a mean of 18.3 ± 16.0 s. Ischemic patients had longer injection site-to-arterial transit times (25.6 versus 20.7 s; P

Lymphedema is a chronic progressive edematous disease that in the United States is most commonly related to malignancy and its treatment. Lymphaticovenular anastomosis is a recently introduced microsurgical treatment option for lymphedema that requires the identification and mapping of individual lymphatic channels. While nuclear medicine lymphoscintigraphy has been the primary imaging modality performed to evaluate suspected lymphedema, lymphoscintigraphy does not provide the spatial information necessary for presurgical planning. High-resolution dynamic 3D magnetic resonance imaging (MRI) can noninvasively image abnormal lymphatic channels to both diagnose lymphedema and depict the location and number of individual lymphatic channels for surgical planning. MR lymphangiography can be performed at 1.5T or 3.0T using multichannel phased array surface coils. The main components of the exam are a heavily T2 -weighted 3D sequence to define the severity and extent of edema, a high-resolution dynamic 3D gradient echo imaging after intracutaneous contrast injection to visualize lymphatic channels, and a delayed 3D gradient echo sequence after intravenous contrast to define veins. This article reviews the pathophysiology and microsurgical treatment of lymphedema, presents the imaging protocol used at our institution, and describes exam interpretation and the image postprocessing performed for surgical planning.

Purpose: To use magnetization tagged magnetic resonance imaging (MRI) (tag-MRI) to quantify cardiac induced liver strain and compare strain of cirrhotic and normal livers. Materials and Methods: Tag-MRI was performed at 1.5T on eight subjects with no history of liver disease and 10 patients with liver cirrhosis. A breath-hold peripheral pulse-gated (PPG) conventional tag-MRI cine sequence was performed with planes to include the left lobe of the liver and the inferior wall of the heart. Commercially available software HARP (Diagnosoft, Palo Alto, CA) was used for image analysis and strain calculation. Three regions-of-interest (ROIs) were selected: segment II of the liver near the heart (A), right liver lobe far from the heart (B), and the left ventricular wall (C). The average and maximal (max) strain were measured in A, B, and C. The maximum strains were used to generate a cardiac-corrected strain gradient: (maxA-maxB)/maxC. Results were compared with Student's t-test (SPSS, Chicago, IL). Results: In subjects with no history of liver disease vs. cirrhotic patients, the average strain was 22% ± 7% vs. 4% ± 3% (P < 0.001), the max strain was 63% ± 15% vs. 17% ± 5% (P < 0.001), and the corrected strain gradient was 0.52 ± 0.16 vs. 0.11% ± 0.08%. Conclusion: There is a significant difference in liver strain measured with tag-MRI between subjects with no history of liver disease and patients with cirrhosis. J. Magn. Reson. Imaging 2012; 36:1490–1495. © 2012 Wiley Periodicals, Inc.

Purpose: To assess the effect of attaining higher spatial resolution in contrast-enhanced magnetic resonance angiography (MRA) of renal arteries using parallel imaging, sensitivity encoding (SENSE), by comparing the SENSE contrast-enhanced (CE) MRA against a conventional CE-MRA protocol with identical scan times, injection protocol, and other acquisition parameters. Materials and Methods: Numerical simulations and a direct comparison of SENSE-accelerated versus conventional acquisitions were performed. A total of 41 patients (18 male) were imaged using both protocols for a direct comparison. Both protocols used fluoroscopic triggering, centric encoding, breath-holding, equivalent injection protocol, and lasted ≈30 seconds. Results: Simulated point-spread functions were narrower for the SENSE protocol compared to the conventional protocol. In the patient study, although the SENSE protocol produced images with lower signal-to-noise ratio (SNR), image quality was better for all segments of the renal arteries. In addition, ringing of kidney parenchyma and renal artery blurring were significantly reduced in the SENSE protocol. Finally, reader confidence improved with the SENSE protocol. Conclusion: Despite a reduction in SNR, the higher-resolution SENSE CE-MRA provided improved image quality, reduced artifacts, and increased reader confidence compared to the conventional protocol. J. Magn. Reson. Imaging 2010;31:149–159. © 2009 Wiley-Liss, Inc.

PURPOSE: To demonstrate that with a priori determination of individual patient hemodynamics, peripheral contrast-enhanced magnetic resonance angiography (pCE-MRA) can be customized to maximize signal-to noise ratio (SNR) and avoid venous enhancement. MATERIALS AND METHODS: Using a 1.5T MRI scanner and prototype 18-channel peripheral vascular (PV) coil designed for highly accelerated parallel imaging, geometry (g)-factor maps were determined. SNR-maximized protocols considering the two-dimensional sensitivity encoding (2D SENSE) factor, TE, TR, bandwidth (BW), and flip angle (FA) were precalculated and stored. For each exam, a small aortic timing bolus was performed, followed by dynamic three-dimensional (3D)-MRA of the calf. Using this information, the aorta to pedal artery and calf arteriovenous transit times were measured. This enabled estimation of the maximum upper and middle station acquisition duration to allow lower station acquisition to begin prior to venous arrival. The appropriately succinct SNR-optimized protocol for each station was selected and moving-table pCE-MRA was performed using thigh venous compression and high-relaxivity contrast material. RESULTS: The protocol was successfully applied in 15 patients and all imaging demonstrated good SNR without diagnosis-hindering venous enhancement. CONCLUSION: By knowing each patient's venous enhancement kinetics, scan parameters can be optimized to utilize maximum possible acquisition time. Some time is added for the timing scans, but in return time-resolved calf CE-MRA, maximized SNR, and decreased risk of venous enhancement are gained.

Purpose To explore the use of breath-hold and navigator-gated noncontrast Steady State Free Precession (SSFP) MR angiography (MRA) protocols for the evaluation of renal artery stenosis (RAS). Materials and Methods Twenty patients referred to rule out RAS were imaged using two breath-hold and one navigator-gated SSFP MRA sequences. All patients underwent contrast-enhanced MRA (CE-MRA). Two radiologists evaluated all sequences both qualitatively (blur, artifacts, reader confidence) and quantitatively (maximum stenosis). Using CE-MRA as truth, a receiver operating characteristics (ROC) curve was generated and a statistical analysis of navigator-gated SSFP (Nav SSFP) was performed. Results Seven patients had >50% renal artery stenosis by CE-MRA. Nav SSFP performed significantly better than either breath-hold SSFP technique in terms of blur, artifacts, and reader confidence. Using a 50% threshold for stenosis, sensitivity for detecting RAS was 100%, with a specificity of 85% and a negative predictive value of 100%. The average mean stenosis difference between Nav SSFP and CE-MRA was 9 ± 9%. Conclusion Nav SSFP outperformed breath-hold SSFP in measures of image quality and reader confidence. Sensitivity and negative predictive value for detecting RAS with Nav SSFP was perfect, with an acceptable specificity of 85%. This suggests further study is warranted to evaluate Nav SSFP as a noncontrast screening technique for renal artery stenosis. J. Magn. Reson. Imaging 2007;26:966–973. © 2007 Wiley-Liss, Inc.

Purpose To determine sequence parameters that maximize vascular contrast-to-noise (CNR) for ultra-high resolution equilibrium phase (EP) peripheral imaging for the blood pool agent (BPA) Vasovist. Materials and Methods A model for maximizing CNR in EP MR angiography (MRA) is presented. Tissue relaxation times, coil geometry (g)-factors, and clinical imaging requirements (voxel volume and scan time) were determined from human studies. Using these known values, parameters for TR, TE, bandwidth, flip angle (FA), and sensitivity encoding (SENSE) factor that maximized CNR were derived from the model. CNR was enhanced by using reduction in scan time gained from parallel imaging to increase TR and minimize bandwidth. A total of 10 patients were imaged using model-derived EP CE-MRA parameters. Results The model closely predicted experimental CNR data measured in two clinical studies (r2 = 0.85) and demonstrated an increase in CNR by a factor of 2.3 when subjects were imaged using optimal sequence parameters (P < 0.001). Thigh and calf data were acquired with voxel volumes on the order of 0.2 mm3 using a SENSE factor of 4. Conclusion Recommended imaging parameters for a 12-channel and 18-channel peripheral vascular coil at two doses of Vasovist (0.03 mmol/kg and 0.05 mmol/kg) are presented. J. Magn. Reson. Imaging 2007;26:580–588. © 2007 Wiley-Liss, Inc.

Purpose To study the potential detrimental effects of renal motion on breath-hold three-dimensional contrast-enhanced (CE) magnetic resonance angiography (MRA). Materials and Methods A computer model simulating linear motion was applied to MRA pulse sequences. Subsequently, to study whether renal motion was present, 24 patients being evaluated for possible renovascular hypertension underwent a breath-hold nonenhanced single slice two-dimensional dynamic turbo field-echo magnetic resonance imaging (MRI) scan with a typical duration of 32 seconds. This sequence was followed by breath-hold three-dimensional CE renal MRA. CE-MRA images were evaluated by two independent observers. Results The computer model revealed linear renal motion to cause artifacts. The severity of these artifacts correlated with velocity. Significant (P < 0.001) near linear cranial motion of the kidneys and diaphragm during a sustained breath-hold was found for the right kidney, left kidney, right diaphragm, and left diaphragm (0.26 ± 0.21 mm/second, 0.25 ± 0.23 mm/second, 0.43 ± 0.43 mm/second, and 0.29 ± 0.33 mm/second [mean ± SD], respectively). CE-MRA images showed artifacts of the distal renal artery that corroborated the computer model findings. Conclusion The observed cranial motion of the kidneys during a breath-hold adversely affects distal renal artery image quality on three-dimensional CE-MRA and jeopardizes reliable clinical evaluation. Shortening scan time may be beneficial for decreasing image degradation caused by this phenomenon. J. Magn. Reson. Imaging 2002;16:685–696. Published 2002 Wiley-Liss, Inc.