Ultrasound Time-Harmonic Elastography of the Aorta: Effect of Age and Hypertension on Aortic Stiffness Objectives The aim of this study was to investigate ultrasound time-harmonic elastography for quantifying aortic stiffness in vivo in the context of aging and arterial hypertension. Materials and Methods Seventy-four participants (50 healthy participants and 24 participants with long-standing hypertension) were prospectively included between January 2018 and October 2018, and underwent ultrasound time-harmonic elastography of the upper abdominal aorta. Compound maps of shear-wave speed (SWS) as a surrogate of tissue stiffness were generated from multifrequency wave fields covering the full field-of-view of B-mode ultrasound. Blood pressure and pulse wave velocity were measured beforehand. Interobserver and intraobserver agreement was determined in 30 subjects. Reproducibility of time-harmonic elastography was assessed in subgroups with repeated measurements after 20 minutes and after 6 months. Linear regression analysis, with subsequent age adjustment of SWS obtained, receiver operating characteristic analysis, and intraclass correlation coefficients (ICCs) were used for statistical evaluation. Results Linear regression analysis revealed a significant effect of age on SWS with an increase by 0.024 m/s per year (P < 0.001). Age-adjusted SWS was significantly greater in hypertensives (0.24 m/s; interquartile range [IQR], 0.17–0.40 m/s) than in healthy participants (0.07 m/s; IQR, −0.01 to 0.06 m/s; P < 0.001). A cutoff value of 0.15 m/s was found to differentiate best between groups (area under the receiver operating characteristic curve, 0.966; 95% confidence interval, 0.93–1.0; P < 0.001; 83% sensitivity and 98% specificity). Interobserver and intraobserver variability was excellent (ICC, 0.987 and 0.937, respectively). Reproducibility was excellent in the short term (ICC, 0.968; confidence interval, 0.878–0.992) and good in the long term (ICC, 0.844; confidence interval, 0.491–0.959). Conclusions Ultrasound time-harmonic elastography of the upper abdominal aorta allows quantification of aortic wall stiffness in vivo and shows significantly higher values in patients with arterial hypertension.

Magnetization Transfer Imaging Is Unaffected by Decreases in Renal Perfusion in Swine Objectives Multiparametric renal magnetic resonance imaging (MRI), including diffusion-weighted imaging, magnetic resonance elastography, and magnetization transfer imaging (MTI), is valuable in the noninvasive assessment of renal fibrosis. However, hemodynamic changes in diseased kidneys may impede their ability to measure renal fibrosis. Because MTI assesses directly tissue content of macromolecules, we test the hypothesis that MTI would be insensitive to renal hemodynamic changes in swine kidneys with acute graded ischemia. Materials and Methods Seven domestic pigs underwent placement of an inflatable silicone cuff around the right renal artery to induce graded renal ischemia. Multiparametric MRI was performed at baseline, 50%, 75%, and 100% renal artery stenosis as well as reperfusion. Measurements included regional perfusion, R2*, apparent diffusion coefficient (ADC), stiffness, and magnetization transfer ratio (MTR) using arterial spin-labeled MRI, blood oxygenation–dependent MRI, diffusion-weighted imaging, magnetic resonance elastography, and MTI, respectively. Histology was performed to rule out renal fibrosis. Results During graded ischemia, decreases in renal perfusion were accompanied with elevated R2*, decreased ADC, and stiffness, whereas no statistically significant changes were observed in the MTR. No fibrosis was detected by histology. After release of the obstruction, renal perfusion showed only partial recovery, associated with return of kidney R2*, ADC, and stiffness to baseline levels, whereas cortical MTR decreased slightly. Conclusions Renal MTI is insensitive to decreases in renal perfusion and may offer reliable assessment of renal structural changes.

Measuring Dynamic CT Perfusion Based on Time-Resolved Quantitative DECT Iodine Maps: Comparison to Conventional Perfusion at 80 kVp for Pancreatic Carcinoma Objectives Using dual-energy computed tomography (DECT) for quantifying iodine content after injection of contrast agent could provide a quantitative basis for dynamic computed tomography (CT) perfusion measurements by means of established mathematical models of contrast agent kinetics, thus improving results by combining the strength of both techniques, which was investigated in this study. Materials and Methods A dynamic DECT acquisition over 51 seconds performed at 80/Sn140 kVp in 17 patients with pancreatic carcinoma was used to calculate iodine-enhancement images for each time point by means of 3-material decomposition. After motion correction, perfusion maps of blood flow were calculated using the maximum-slope model from both 80 kVp image data and iodine-enhancement images. Blood flow was measured in regions of interest placed in healthy pancreatic tissue and carcinoma for both of the derived perfusion maps. To assess image quality of input data, an adjusted contrast-to-noise ratio was calculated for 80 kVp images and iodine-enhancement images. Susceptibility of perfusion results to residual patient breathing motion during acquisition was investigated by measuring blood flow in fatty tissue surrounding the pancreas, where blood flow should be negligible compared with the pancreas. Results For both 80 kVp and iodine-enhancement images, blood flow was significantly higher in healthy tissue (114.2 ± 37.4 mL/100 mL/min or 115.1 ± 36.2 mL/100 mL/min, respectively) than in carcinoma (46.5 ± 26.6 mL/100 mL/min or 49.7 ± 24.7 mL/100 mL/min, respectively). Differences in blood flow between 80 kVp image data and iodine-enhancement images were statistically significant in healthy tissue, but not in carcinoma. For 80 kVp images, adjusted contrast-to-noise ratio was significantly higher (1.3 ± 1.1) than for iodine-enhancement images (1.1 ± 0.9). When evaluating fatty tissue surrounding the pancreas for estimating influence of patient motion, measured blood flow was significantly lower for iodine-enhancement images (30.7 ± 12.0 mL/100 mL/min) than for 80 kVp images (39.0 ± 19.1 mL/100 mL/min). Average patient radiation exposure was 8.01 mSv for dynamic DECT acquisition, compared with 4.60 mSv for dynamic 80 kVp acquisition. Discussion Iodine enhancement images can be used to calculate CT perfusion maps of blood flow, and compared with 80 kVp images, results showed only a small difference of 1 mL/100 mL/min in blood flow in healthy tissue, whereas patient radiation exposure was increased for dynamic DECT. Perfusion maps calculated based on iodine-enhancement images showed lower blood flow in fatty tissues surrounding the pancreas, indicating reduced susceptibility to residual patient breathing motion during the acquisition.

Tumor Contrast Enhancement and Whole-Body Elimination of the Manganese-Based Magnetic Resonance Imaging Contrast Agent Mn-PyC3A Objectives The goals of this study were to compare the efficacy of the new manganese-based magnetic resonance imaging (MRI) contrast agent Mn-PyC3A to the commercial gadolinium-based agents Gd-DOTA and to Gd-EOB-DTPA to detect tumors in murine models of breast cancer and metastatic liver disease, respectively, and to quantify the fractional excretion and elimination of Mn-PyC3A in rats. Methods T1-weighted contrast-enhanced MRI with 0.1 mmol/kg Mn-PyC3A was compared with 0.1 mmol/kg Gd-DOTA in a breast cancer mouse model (n = 8) and to 0.025 mmol/kg Gd-EOB-DTPA in a liver metastasis mouse model (n = 6). The fractional excretion, 1-day biodistribution, and 7-day biodistribution in rats after injection of 2.0 mmol/kg [52Mn]Mn-PyC3A or Gd-DOTA were quantified by 52Mn gamma counting or Gd elemental analysis. Imaging data were compared with a paired t test; biodistribution data were compared with an unpaired t test. Results The postinjection-preinjection increases in tumor-to-muscle contrast-to-noise ratio (ΔCNR) 3 minutes after injection of Mn-PyC3A and Gd-DOTA (mean ± standard deviation) were 17 ± 3.8 and 20 ± 4.4, respectively (P = 0.34). Liver-to-tumor ΔCNR values at 8 minutes postinjection of Mn-PyC3A and Gd-EOB-DTPA were 28 ± 9.0 and 48 ± 23, respectively (P = 0.11). Mn-PyC3A is eliminated with 85% into the urine and 15% into the feces after administration to rats. The percentage of the injected doses (%ID) of Mn and Gd recovered in tissues after 1 day were 0.32 ± 0.12 and 0.57 ± 0.12, respectively (P = 0.0030), and after 7 days were 0.058 ± 0.051 and 0.19 ± 0.052, respectively (P < 0.0001). Conclusions Mn-PyC3A provides comparable tumor contrast enhancement to Gd-DOTA in a mouse breast cancer model and is more completely eliminated than Gd-DOTA; partial hepatobiliary elimination of Mn-PyC3A enables conspicuous delayed phase visualization of liver metastases.

Modulating Diffusion-Weighted Magnetic Resonance Imaging for Screening in Oncologic Tertiary Prevention: A Prospective Ex Vivo and In Vivo Study Introduction Diffusion-weighted imaging (DWI) is an important part of oncological magnetic resonance imaging (MRI) examinations, especially for tertiary cancer prevention in terms of early detection of recurrent disease. However, abdominal studies can be challenged by motion artifacts, poor signal-to-noise ratios, and visibility of retroperitoneal structures, which necessitates sequence optimization depending on the investigated region. This study aims at prospectively evaluating an adapted DWI sequence ex vivo and in vivo in oncologic patients undergoing abdominal MRI. Methods This institutional review board–approved, prospective study included phantom measurements, volunteer examinations, and oncologic patient examinations of the abdomen. Fifty-seven MRI examinations in 54 patients (mean age, 58 years; range, 21–90 years) were included into the analysis. The MRI examination were performed at a 1.5 T MRI scanner (MAGNETOM Aera; Siemens Healthcare, Erlangen, Germany) and included both a standard EPI-DWI (s-DWI; b = 50, 900 s/mm2) and an adapted DWI (opt-DWI; EPI-DWI with b = 0, 50, 900, 1500 s/mm2, acquisition with higher spatial resolution and optimized processing for the abdomen including motion correction, adaptive image combination, and background suppression). For b = 900 s/mm2, the ratio of signal intensity in the normal tissue and the standard deviation of the noise in the surrounding air was quantitatively calculated; image quality and tissue differentiation parameters were rated by 2 independent, blinded readers using a 5-point Likert scale. Statistics included Wilcoxon signed-rank test and kappa statistic (P < 0.05/0.0125 after Bonferroni correction). Results The DWI phantom demonstrated an optimized contour sharpness and inlay differentiation for opt-DWI. The apparent ratio of normal tissue signal/standard deviation of background noise at b = 900 s/mm2 of the right/left hemiabdomen was significantly increased in opt-DWI (mean, 71.9 ± 23.5/86.0 ± 43.3) versus s-DWI (mean, 51.4 ± 15.4/63.4 ± 36.5; P < 0.001). Image quality parameters (contour sharpness and tissue differentiation of upper abdominal and retroperitoneal structures) were significantly increased in opt-DWI versus s-DWI (P < 0.001). Interreader reliability test showed good agreement (kappa = 0.768; P < 0.001). Discussion This study prospectively evaluated the potential of adapted DWI for screening in tertiary prevention of oncologic patients. An optimized DWI protocol with advanced processing achieved improved image quality in quantitative and qualitative analyses. Oncological optimization of DWI should be performed before its application in cancer patients to improve both screening and follow-up examinations, to better unleash the diagnostic potential of DWI.

Three Tesla 3D High-Resolution Vessel Wall MRI of the Orbit may Differentiate Arteritic From Nonarteritic Anterior Ischemic Optic Neuropathy Background Anterior ischemic optic neuropathy (AION) is the most common cause of acute optic neuropathy in older patients. Distinguishing between arteritic AION (A-AION) and nonarteritic (NA-AION) is paramount for improved patient management. Purpose The aim of this study was to evaluate 3-dimensional high-resolution vessel wall (HR-VW) magnetic resonance imaging (MRI) at 3 T to discriminate A-AION from NA-AION. Materials and Methods This prospective single-center study was approved by a national research ethics board and included 27 patients (17 A-AION and 10 NA-AION) with 36 AIONs from December 2014 to August 2017 who underwent 3 T HR-VW MRI. Two radiologists blinded to clinical data individually analyzed the imaging separately and in random order. Discrepancies were resolved by consensus with a third neuroradiologist. The primary diagnostic criterion was the presence of inflammatory changes of the ophthalmic artery. Secondary diagnostic criteria included the presence of an enhancement of the optic nerve or its sheath, the optic disc, or inflammatory changes of posterior ciliary or extracranial arteries. A Fisher exact test was used to compare A-AION from NA-AION patients. Results Inflammatory changes of the ophthalmic artery were present in all patients with A-AION but in none of NA-AION (P < 0.0001). Its sensitivity, specificity, positive predictive value, and negative predictive value were 100%. Inflammatory changes of posterior ciliary arteries were significantly more likely in A-AOIN (82% vs 0%, P < 0.0001). Interreader and intrareader agreements were almost perfect (κ = 0.82–1). Conclusions High-resolution vessel wall MRI seems highly accurate when distinguishing A-AION from NA-AION and might be useful to improve patient management.

Transcranial Shear Wave Elastography of Neonatal and Infant Brains for Quantitative Evaluation of Increased Intracranial Pressure Objectives Increased intracranial pressure (ICP) in neonates and infants is a severe disease state that requires adequate diagnosis and, depending on the clinical situation and whether it is increasing, a rapid and efficient therapy. Clinical evaluation, B-mode ultrasound, and Doppler ultrasound give rise to a basic noninvasive diagnosis of increased ICP. The purpose of this prospective study was 2-fold: first, to analyze the technical feasibility of obtaining shear wave elastography (SWE) measurements of an infant's brain, and second, to compare the values of healthy neonates to those who have hydrocephalus and are either suspected of having or invasively shown to have increased ICP. Materials and Methods This was a prospective, institutional review board–approved study of 184 neonates and infants with a mean age of 12 weeks (ranging from 1 day to 12 months). The final, technical evaluable cohort consisted of 166 infants, of whom 110 were healthy asymptomatic infants and 56 were diagnosed with hydrocephalus. Of the latter, 38 showed clinically increased ICP and 18 did not. Invasive ICP measurements were available from 47 of the children. All infants underwent systematic examination using B-mode ultrasound, Doppler ultrasound, and SWE using a high-resolution linear 15-MHz probe (Aixplorer; Supersonic), by 1 of 2 radiologists, each of whom had at least 5 years' experience examining children's brains and applying SWE. Semiquantitative and quantitative SWE measurements were performed. We compared the SWE values to each participant's clinical symptoms and to their invasive ICP measurement results. Correlations were calculated using Pearson and Spearman correlation coefficients. We used Student t test to compare the mean SWE values in healthy children to those of children with increased ICP. Results Shear wave elastography in the brain was technically feasible, giving reliable SWE measurements in 110 (88.7%) of 124 of healthy children and in 56 (93.3%) of 60 children with hydrocephalus. Shear wave elastography values and, thus, rigidity in the brain's parenchyma were significantly higher in children with hydrocephalus (n = 56) than in healthy children (n = 110; mean, 21.8 kPa vs 14.1 kPa; P = 0.0083). A thorough correlation between invasive ICP measurements and SWE values in a subgroup of patients with hydrocephalus revealed a direct correlation between increased ICP and increased SWE values (r = 0.69, P < 0.001). Mean SWE values were 30.8 kPa (range, 23.9–62.3 kPa) in patients with confirmed increased ICP (n = 35) versus 16.2 kPa (range, 10.2–41.9 kPa) in patients with nonincreased ICP (n = 12). Conclusions Shear wave elastography is feasible in neonates with increased ICP and could be a useful additional diagnostic imaging and monitoring method for children verified or suspected to have increased ICP. However, more evidence is necessary to further evaluate the usefulness of SWE measurements in neonates with hydrocephalus. Clinical Relevance Shear wave elastography can be used as a surrogate marker for ICP in neonates and infants.

Free-Breathing Dynamic Contrast-Enhanced Imaging of the Upper Abdomen Using a Cartesian Compressed-Sensing Sequence With Hard-Gated and Motion-State-Resolved Reconstruction Objectives The aim of this study was to compare a compressed-sensing free-breathing VIBE (fbVIBE) with a conventional breath-hold VIBE (bhVIBE) for dynamic contrast-enhanced imaging of the upper abdomen. Materials and Methods In total, 70 datasets (bhVIBE, n = 30; fbVIBE n = 40; hard-gated [hg] reconstruction, n = 30; motion-state-resolved [mr] reconstruction, n = 10) were assessed by 2 experienced readers. Both sequences were performed on 1.5-T magnetic resonance imaging scanners. The prototypical fbVIBE sequence acquired a navigation signal along with the imaging data and supported 2 different reconstructions: an hg reconstruction that either accepted or rejected an echo train based on the navigation signal and an mr reconstruction that assigned echo trains to their determined motion states. The hg reconstruction to reduce respiratory motion artifacts was carried out inline on the scanner (duration: approximately 8 minutes on the scanner-integrated CPU). The mr reconstruction delivered better results, but the reconstruction time is multiplied by the number of selected motion states (6 in the current study). Comparable reconstruction times to hg reconstruction can only be achieved on GPU-supported scanners. Therefore, the acquired raw data were selectively reconstructed at a later timepoint (duration: approximately 45 minutes). Welch analysis of variance tests were applied to compare image quality (IQ), delineation of structures, artifacts, and diagnostic confidence, which were rated on Likert-type scales (IQ/delineation of structures/diagnostic confidence: 1 [nondiagnostic] to 5 [perfect]; artifacts: 1 [no artifacts] to 5 [severe artifacts]). Mann-Whitney U tests and Kruskal-Wallis H tests were used to compare the extent of artifacts in older (aged ≥70 years) and younger (aged <70 years) patients. Interobserver agreement was assessed using Cohen κ. Results Mean ratings for IQ/delineation of structures/diagnostic confidence of fb(hg)VIBE (4.2 ± 0.7/4.3 ± 0.8/4.3 ± 0.7; κ = 0.8/0.7/0.6) and fb(mr)VIBE (4.9 ± 0.3/4.9 ± 0.3/4.9 ± 0.3; κ = 0.3/1/0.9) were higher compared with those of bhVIBE (3.7 ± 0.8/3.8 ± 0.8/3.9 ± 0.9; κ = 0.9/0.9/0.9), whereas artifacts of fb(hg)VIBE/fb(mr)VIBE were rated lower (fb[hg]VIBE/fb[mr]VIBE/bhVIBE = 2.2 ± 0.9/1.3 ± 0.5/2.4 ± 0.9; κ = 0.6/0.6/0.9). The IQ of fb(hg)VIBE was rated significantly higher compared with that of bhVIBE (P = 0.03). All parameters were significantly improved by mr reconstruction compared with fb(hg)VIBE and bhVIBE (P < 0.001). In the fb(hg)VIBE cohort, an insignificant trend toward lower artifacts in the younger age group (≥70 years: 2.5 ± 0.9 vs <70 years: 1.9 ± 0.8) was found, whereas significant differences emerged in the bhVIBE cohort (≥70 years: 3 ± 0.9 vs <70 years: 2.1 ± 0.9; P = 0.02). Conclusions Fast fbVIBE using hg and mr reconstructions is technically feasible with improved IQ compared with that of bhVIBE. Free-breathing VIBE may be useful for dynamic contrast-enhanced of the upper abdomen, particularly in older and/or severely ill patients with impaired breath-hold capabilities.