Aparna Singhal

Ultra-low-dose, time-resolved contrast-enhanced magnetic resonance angiography of the carotid arteries at 3.0 tesla.

Purpose:To determine whether time-resolved magnetic resonance angiography (TR-MRA) with ultra-low-dose gadolinium chelate (1.5–3.0 mL) can reliably detect or rule out hemodynamically significant disease in the carotid-vertebral artery territory. Materials and Methods:Hundred consecutive patients (62 women, 38 men, mean age = 56.6 years) underwent both TR-MRA and standard high-resolution contrast-enhanced magnetic resonance angiography (CE-MRA), having been randomized to 1 of 2 groups; group A receiving a contrast dose of 1.5 mL for TR-MRA and group B receiving 3.0 mL. For scoring purposes the arterial system was divided into 21 segments. All TR-MRA and CE-MRA studies were blindly assessed by 2 radiologists for overall image quality, segmental arterial visualization, grading of arterial stenosis/occlusion, and incidence and severity of artifact. TR-MRA findings were directly compared with those of the corresponding CE-MRA examinations. Results:Group A TR-MRA studies were of significantly inferior overall image quality compared with those of the corresponding CE-MRA examinations (P = 0.01 for both observers). In group B, overall image quality was similar for TR-MRA and single-phase CE-MRA examinations. On a segmental basis, a higher number of “insufficient quality” segments were identified in group A TR-MRA studies than in group B. A similar reduction in the incidence of artifacts was observed for group B relative to group A TR-MRA studies. Both groups A and B TR-MRA studies were of high specificity, negative predictive values, and accuracy (>97%). Conclusion:Ultra-low dose TR-MRA may be performed with 3 mL of gadolinium chelate with preservation of overall image quality and arterial segmental visualization relative to single phase CE-MRA, whereas a 1.5 mL contrast dose is associated with more suboptimal studies. Nonetheless, even at doses as low as 1.5 mL, TR-MRA can exclude arterial stenosis or occlusion.

Noncontrast 3D Steady State Free Precession Magnetic Resonance Angiography of the Thoracic Central Veins Using Nonselective Radiofrequency Excitation Over a Large Field of View : Initial Experience

Purpose:To evaluate the feasibility of three-dimensional (3D) steady state free precession (SSFP) magnetic resonance angiography (MRA) using nonselective radiofrequency excitation for the assessment of thoracic central veins. Materials and Methods:Thirty consecutive patients (17 males, 13 females, age range 22–76) with various cardiac and thoracic vascular diseases underwent free-breathing electrocardiogram-gated noncontrast SSFP MRA and conventional high-resolution 3D contrast-enhanced (CE) MRA of the thorax at 1.5 T. Two readers evaluated both datasets for findings: venous visibility and sharpness (from 0, not visualized to 3, excellent definition); artifacts; signal-to-noise ratio (SNR); and contrast-to-noise ratio (CNR) in 8 venous segments including superior vena cava (SVC), supra-diaphragmatic inferior vena cava, bilateral brachiocephalic, proximal subclavian, and lower internal jugular veins. Statistical analysis was performed using Wilcoxon test for overall image quality and vessel visibility, t test for SNR and CNR analysis, and kappa coefficient for inter-observer variability. Results:3D SSFP and CE-MRA were successfully performed in all patients. Scan time for SSFP MRA ranged from 5 to 10 minutes (mean ± standard deviation, 7 ± 2 minutes). Reader 1 (2) graded the overall image quality as excellent and good on SSFP MRA in 23 (25) and 7 (5) patients, and on CE-MRA in 22 (23) and 8 (9) patients, respectively. On SSFP MRA, readers 1 and 2 graded 234 (97.5%) and 233 (97.1%) venous segments with diagnostic definition (grades 2 and 3) (κ = 0.69), respectively. On conventional CE-MRA, readers 1 and 2 graded 231 (96.3%) and 232 (96.7%) venous segments with diagnostic definition (grades 2 and 3) (κ = 0.68), respectively. Segmental visibility and sharpness were higher for lower internal jugular veins on CE-MRA for each reader (P < 0.001). No significant difference existed for venous visibility and sharpness scores for other venous segments between the 2 techniques for both readers (P > 0.05). SNR and CNR values were lower for internal jugular veins on SSFP MRA (P < 0.001). No significant difference existed between SNR and CNR values for the other venous segments on SSFP and CE-MRA (P > 0.05 for all). The 2 readers demonstrated patent SVC Glenn shunt to main pulmonary artery (n = 3), patent extra cardiac Fontan shunt from inferior vena cava to pulmonary artery confluence (n = 2), and dilatation and thrombosis of SVC (n = 1) and right brachiocephalic vein (n = 1) on both datasets. Conclusion:Free breathing navigator-gated noncontrast 3D SSFP MRA with nonselective radiofrequency excitation provides high image quality and sufficient SNR and CNR for confident evaluation of thoracic central veins.

Two-dimensional MR spectroscopy of minimal hepatic encephalopathy and neuropsychological correlates in vivo.

To evaluate regional cerebral metabolic and structural changes in patients with minimal hepatic encephalopathy (MHE) using two‐dimensional (2D) MR spectroscopy (MRS) and T   1 ‐weighted MRI, to correlate the observed MR changes with neuropsychological (NP) test scores, and to compare the diagnostic accuracy of MRI, 2D MRS, and NP tests in discriminating between patients and healthy subjects.

Three-dimensional imaging of pulmonary veins by a novel steady-state free-precession magnetic resonance angiography technique without the use of intravenous contrast agent: initial experience.

Purpose:To evaluate the feasibility of 3-dimensional (3D) steady-state free-precession (SSFP) magnetic resonance angiography (MRA) using nonselective radiofrequency excitation for imaging of pulmonary veins (PVs) without intravenous gadolinium chelate and to correlate the results with conventional contrast-enhanced MRA (CE-MRA). Material and Methods:Forty consecutive patients with history of atrial fibrillation underwent free-breathing respiratory navigator-gated electrocardiogram-triggered SSFP MRA without contrast administration and conventional high-resolution 3D CE-MRA of the thorax at 1.5 T. Two readers assessed both datasets for vascular definition (from 0, not visualized, to 3, excellent definition), artifacts, and ostial diameters. Statistical analysis was performed using Wilcoxon, paired t test, and kappa coefficient. Results:On SSFP MRA, readers 1 and 2 graded 96.4% (160/166) and 97% (161/166) of the segments as having diagnostic visibility and sharpness, respectively (k = 0.82). On CE-MRA datasets, all segments were graded as having diagnostic visibility and sharpness by both readers (k = 0.86). No significant difference existed for visibility and sharpness of pulmonary venous segments between the datasets for each reader (P[r] > 0.05). Reader 1 (2) identified 27 (28) and 35 (32) motion artifacts on SSFP and CE-MRA datasets, respectively. No significant difference was found to exist between ostial diameters on CE-MRA and SSFP datasets (P > 0.05). Conclusion:Our study shows that 3D depiction of PVs without intravenous contrast is feasible with nonslice-selective SSFP MRA. This novel MRA technique may be used in certain patients with atrial fibrillation to assess the number and size of PV ostia draining to the left atrium prior to radiofrequency ablation.

Characterization of Intra-myocellular Lipids using 2D Localized Correlated Spectroscopy and Abdominal Fat using MRI in Type 2 Diabetes

A major goal of this pilot study was to quantify intramyocellular lipids (IMCL), extramyocellular lipids (EMCL), unsaturation index (UI) and metabolites such as creatine (Cr), choline (Ch) and carnosine (Car), in the soleus muscle using two-dimensional (2D) localized correlated spectroscopy (L-COSY). Ten subjects with type 2 diabetes (T2D), controlled by lifestyle management alone, and 9 healthy control subjects, were studied. In T2D patients only, the following measurements were obtained: body mass index (BMI); waist circumference (WC); abdominal visceral and subcutaneous fat quantified using breath-held magnetic resonance imaging (MRI); a fasting blood draw for assessment of glucose, insulin, and estimation of homeostasis model assessment of insulin resistance (HOMA-IR), HbA1c, and high-sensitivity c-reactive protein (hs-CRP). Analysis of the soleus muscle 2D L-COSY spectral data showed significantly elevated IMCL ratios with respect to Cr and decreased IMCL UI in T2D when compared to healthy subjects (P < 0.05). In T2D subjects, Pearson correlation analysis showed a positive correlation of IMCL/Cr with EMCL/Cr (0.679, P < 0.05) and HOMA-IR (0.633, P < 0.05), and a non-significant correlation of visceral and subcutaneous fat with magnetic resonance spectroscopy (MRS) and other metrics. Characterization of muscle IMCL and EMCL ratios, UI, and abdominal fat, may be useful for the noninvasive assessment of the role of altered lipid metabolism in the pathophysiology of T2D, and for assessment of the effects of future therapeutic interventions designed to alter metabolic dysfunction in T2D.

Magnetic resonance T2‐relaxometry and 2D L‐correlated spectroscopy in patients with minimal hepatic encephalopathy

To evaluate T2‐relaxation changes in patients with minimal hepatic encephalopathy (MHE) using T2 relaxometry and to correlate T2 values with brain metabolites evaluated using 2D magnetic resonance spectroscopy (MRS).

Assessment of cerebral arteriovenous malformations with high temporal and spatial resolution contrast-enhanced magnetic resonance angiography: a review from protocol to clinical application.

The combination of high spatial and high temporal resolution contrast-enhanced magnetic resonance angiography (MRA) at 3.0 T has enabled the detailed evaluation of functional vascular anatomy and hemodynamics of cerebral arteriovenous malformations (AVMs). Key contributory technical factors for the successful implementation of MRA in patients with different vascular pathologies are multicoil and multichannel receiver arrays, which enable higher parallel acquisition at 3.0 T over a uniform and a large field of view for highly temporally and spatially resolved MRA. Magnetic resonance angiography enables both screening of patients with suspected AVMs and follow-up of patients after therapy. It allows the characterization of AVMs with respect to nidus configuration, size, venous drainage, and so on, according to the Spetzler-Martin classification.

156 Pulmonary vein imaging by 3D non-contrast, free breathing SSFP MR angiography; a novel technique

Introduction Radiofrequency ablation of foci in pulmonary veins has emerged as a therapeutic option for patients with medically refractory atrial fibrillation or those unable to tolerate drugs. Preprocedural imaging is important and is being increasingly utilized to assess pulmonary venous anatomy. Contrast enhanced Magnetic Resonance Angiography (CEMRA) has been shown to be an efficient modality for assessment of pulmonary veins with excellent spatial resolution without any exposure to radiation and iodinated contrast. However, CE-MRA is operator dependant and requires patient cooperation for breath holding. Additionally, high dose gadolinium use has been recently reported to be associated with the occurrence of Nephrogenic Systemic Fibrosis (NSF) in certain patients including renal disease patients. Recently, three dimensional navigator gated free breathing selective steady-state free precession (SSFP) sequence has been employed to display non-contrast MR angiography of the heart and great vessels. The SSFP causes inherent high contrast between the blood pool and background tissues in the body due to high T2/T1 ratio.

1053 Assessment of complex peripheral vascular malformations with highly time-resolved 3D contrast-enhanced MR angiography and single phase high-spatial resolution 3D contrast-enhanced MRA at 3.0 Tesla

Introduction Over the past few years, contrast enhanced MR angiography (CE-MRA) techniques have emerged as non-invasive and safe alternative imaging approaches for comprehensive imaging of upper and lower extremity vascular malformations. Due to its high-spatial resolution, singlephase CE-MRA is desirable for evaluation of the anatomical extent and morphological details of these lesions. However, this technique is limited in providing functional and dynamic information of vascular malformations. Rapid dynamic viewing is necessary for appropriate visualization of arteries from veins in lesions with fast flow such as peripheral arteriovenous malformations (AVMs). Time resolved MRA provides dynamic information which are complementary to conventional MRA by showing the flow dynamics of these disorders, demonstrating feeding arteries or draining veins, and differentiating a slow from high flow lesion.