Scott K. Nagle

Optimized 3D ultrashort echo time pulmonary MRI

To optimize 3D radial ultrashort echo time MRI for high resolution whole‐lung imaging.

Clinical multishot DW‐EPI through parallel imaging with considerations of susceptibility, motion, and noise

Geometric distortions and poor image resolution are well known shortcomings of single‐shot echo‐planar imaging (ss‐EPI). Yet, due to the motion immunity of ss‐EPI, it remains the most common sequence for diffusion‐weighted imaging (DWI). Moreover, both navigated DW interleaved EPI (iEPI) and parallel imaging (PI) methods, such as sensitivity encoding (SENSE) and generalized autocalibrating parallel acquisitions (GRAPPA), can improve the image quality in EPI. In this work, DW‐EPI accelerated by PI is proposed as a self‐calibrated and unnavigated form of interleaved acquisition. The PI calibration is performed on the b = 0 s/mm2 data and applied to each shot in the rest of the DW data set, followed by magnitude averaging. Central in this study is the comparison of GRAPPA and SENSE in the presence of off‐resonances and motion. The results show that GRAPPA is more robust than SENSE against both off‐resonance and motion‐related artifacts. The SNR efficiency was also investigated, and it is shown that the SNR/scan time ratio is equally high for one‐ to three‐shot high‐resolution diffusion scans due to the shortened EPI readout train length. The image quality improvements without SNR efficiency loss, together with motion tolerance, make the GRAPPA‐driven DW‐EPI sequence clinically attractive. Magn Reson Med 57:881–890, 2007.

Hepatobiliary MR imaging with gadolinium-based contrast agents

The advent of gadolinium‐based “hepatobiliary” contrast agents offers new opportunities for diagnostic magnetic resonance imaging (MRI) and has triggered great interest for innovative imaging approaches to the liver and bile ducts. In this review article we discuss the imaging properties of the two gadolinium‐based hepatobiliary contrast agents currently available in the U.S., gadobenate dimeglumine and gadoxetic acid, as well as important pharmacokinetic differences that affect their diagnostic performance. We review potential applications, protocol optimization strategies, as well as diagnostic pitfalls. A variety of illustrative case examples will be used to demonstrate the role of these agents in detection and characterization of liver lesions as well as for imaging the biliary system. Changes in MR protocols geared toward optimizing workflow and imaging quality are also discussed. It is our aim that the information provided in this article will facilitate the optimal utilization of these agents and will stimulate the readers pursuit of new applications for future benefit. J. Magn. Reson. Imaging 2012;35:492‐511.

High resolution navigated three‐dimensional T1‐weighted hepatobiliary MRI using gadoxetic acid optimized for 1.5 tesla

To determine optimal delay times and flip angles for T1‐weighted hepatobiliary imaging at 1.5 Tesla (T) with gadoxetic acid and to demonstrate the feasibility of using a high‐resolution navigated optimized T1‐weighted pulse sequence to evaluate biliary disease.

Optimized high-resolution contrast-enhanced hepatobiliary imaging at 3 tesla: a cross-over comparison of gadobenate dimeglumine and gadoxetic acid.

To evaluate the signal to noise ratio (SNR) and contrast to noise ratio (CNR) performance of 0.05 mmol/kg gadoxetic acid and 0.1 mmol/kg gadobenate dimeglumine for dynamic and hepatobiliary phase imaging. In addition, flip angles (FA) that maximize relative contrast‐to‐noise performance for hepatobiliary phase imaging were determined.

Functional imaging of the lungs with gas agents

This review focuses on the state‐of‐the‐art of the three major classes of gas contrast agents used in magnetic resonance imaging (MRI)—hyperpolarized (HP) gas, molecular oxygen, and fluorinated gas—and their application to clinical pulmonary research. During the past several years there has been accelerated development of pulmonary MRI. This has been driven in part by concerns regarding ionizing radiation using multidetector computed tomography (CT). However, MRI also offers capabilities for fast multispectral and functional imaging using gas agents that are not technically feasible with CT. Recent improvements in gradient performance and radial acquisition methods using ultrashort echo time (UTE) have contributed to advances in these functional pulmonary MRI techniques. The relative strengths and weaknesses of the main functional imaging methods and gas agents are compared and applications to measures of ventilation, diffusion, and gas exchange are presented. Functional lung MRI methods using these gas agents are improving our understanding of a wide range of chronic lung diseases, including chronic obstructive pulmonary disease, asthma, and cystic fibrosis in both adults and children. J. Magn. Reson. Imaging 2016;43:295–315.

Effectiveness of MR angiography for the primary diagnosis of acute pulmonary embolism: clinical outcomes at 3 months and 1 year.

To determine the effectiveness of MR angiography for pulmonary embolism (MRA‐PE) in symptomatic patients.

Detection of small pulmonary nodules with ultrashort echo time sequences in oncology patients by using a PET/MR system

PURPOSE To investigate the utility of a free-breathing ultrashort echo time (UTE) sequence for the evaluation of small pulmonary nodules in oncology patients by using a hybrid positron emission tomography (PET)/magnetic resonance (MR) imaging system and to compare the nodule detection rate between UTE and a conventional three-dimensional gradient-recalled-echo (GRE) technique. MATERIALS AND METHODS In this HIPAA-compliant, institutional review board-approved prospective study, 82 pulmonary nodules were identified in eight patients with extrathoracic malignancies. Patients underwent free-breathing UTE and dual-echo three-dimensional GRE imaging of the lungs in a hybrid PET/MR imaging unit immediately after clinical PET/computed tomography (CT). CT was considered the reference standard for nodule detection. Two reviewers identified nodules and obtained measurements on MR images. The McNemar test was used to evaluate differences in nodule detection rate between MR techniques, and interrater agreement was assessed by using Bland-Altman plots. RESULTS Mean nodule diameter ± standard deviation was 6.2 mm ± 2.7 (range, 3-17 mm). The detection rate was higher for UTE imaging than for dual-echo GRE imaging for nodules of at least 4 mm (82% vs 34%, respectively; P < .001), with the largest difference in detection noted in the 4-8-mm nodule group (79% vs 21%, P < .001). UTE imaging displayed a higher detection rate than dual-echo GRE imaging for nodules without fluorodeoxyglucose avidity (68% vs 22%, respectively; P < .001). Interrater reliability of nodule detection with MR imaging was high (κ = 0.90 for UTE imaging and κ = 0.92 for dual-echo GRE imaging). CONCLUSION A free-breathing UTE sequence has high sensitivity for the detection of small pulmonary nodules (4-8 mm) and outperformed a three-dimensional dual-echo GRE technique for the detection of small, non-fluorodeoxyglucose-avid nodules.

Oxygen-enhanced 3D radial ultrashort echo time magnetic resonance imaging in the healthy human lung

The purpose of this work was to use 3D radial ultrashort echo time (UTE) MRI to perform whole‐lung oxygen‐enhanced (OE) imaging in humans.

Hyperpolarized Helium-3 MRI of Exercise-Induced Bronchoconstriction During Challenge and Therapy

To investigate the utility of hyperpolarized He‐3 MRI for detecting regional lung ventilated volume (VV) changes in response to exercise challenge and leukotriene inhibitor montelukast, human subjects with exercise induced bronchoconstriction (EIB) were recruited. This condition is described by airway constriction following exercise leading to reduced forced expiratory volume in 1 second (FEV1) coinciding with ventilation defects on hyperpolarized He‐3 MRI.