Early proton magnetic resonance spectroscopy during and after therapeutic hypothermia in perinatal hypoxic-ischemic encephalopathy.

BACKGROUND: Hypoxic-ischemic encephalopathy (HIE) remains a significant cause of mortality and neurodevelopmental impairment despite treatment with therapeutic hypothermia. Magnetic resonance H1-spectroscopy measures concentrations of cerebral metabolites to detect derangements in aerobic metabolism. OBJECTIVE: We assessed MR spectroscopy in neonates with HIE within 18-24 h of initiating therapeutic hypothermia and at 5-6 days post therapeutic hypothermia. MATERIALS AND METHODS: Eleven neonates with HIE underwent MR spectroscopy of the basal ganglia and white matter. We compared metabolite concentrations during therapeutic hypothermia and post-therapeutic hypothermia and between moderate and severe HIE. RESULTS: During therapeutic hypothermia, neonates with severe HIE had decreased basal ganglia N-acetylaspartate (NAA; 0.62±0.08 vs. 0.72±0.05; P=0.02), NAA + N-acetylaspartylglutamate (NAAG; 0.66±0.11 vs. 0.77±0.06; P=0.05), glycerophosphorylcholine + phosphatidylcholine (GPC+PCh; 0.28±0.05 vs. 0.38±0.06; P=0.02) and decreased white matter GPC+PCh (0.35±0.13 vs. 0.48±0.04; P=0.02) compared to neonates with moderate HIE. For all subjects, basal ganglia NAA decreased (-0.08±0.07; P=0.01), whereas white matter GPC+PCh increased (0.03±0.04; P=0.04) from therapeutic hypothermia MRI to post-therapeutic-hypothermia MRI. All metabolite values are expressed in mmol/L. CONCLUSION: Decreased NAA and GPC+PCh were associated with greater HIE severity and could distinguish neonates who might benefit most from targeted additional neuroprotective therapies.

Cerebral oxygen metabolism during and after therapeutic hypothermia in neonatal hypoxic-ischemic encephalopathy: a feasibility study using magnetic resonance imaging.

BACKGROUND: Therapeutic hypothermia is the standard-of-care treatment for infants diagnosed with moderate-to-severe hypoxic-ischemic encephalopathy (HIE). MRI for assessing brain injury is usually performed after hypothermia because of logistical challenges in bringing acutely sick infants receiving hypothermia from the neonatal intensive care unit (NICU) to the MRI suite. Perhaps examining and comparing early cerebral oxygen metabolism disturbances to those after rewarming will lead to a better understanding of the mechanisms of brain injury in HIE and the effects of therapeutic hypothermia. OBJECTIVE: The objectives were to assess the feasibility of performing a novel T2-relaxation under spin tagging (TRUST) MRI technique to measure venous oxygen saturation very early in the time course of treatment, 18-24 h after the initiation of therapeutic hypothermia, to provide a framework to measure neonatal cerebral oxygen metabolism noninvasively, and to compare parameters between early and post-hypothermia MRIs. MATERIALS AND METHODS: Early (18-24 h after initiating hypothermia) MRIs were performed during hypothermia treatment in nine infants with HIE (six with moderate and three with severe HIE). Six infants subsequently had an MRI after hypothermia. Mean values of cerebral blood flow, oxygen extraction fraction, and cerebral metabolic rate of oxygen from MRIs during hypothermia were compared between infants with moderate and severe HIE; and in those with moderate HIE, we compared cerebral oxygen metabolism parameters between MRIs performed during and after hypothermia. RESULTS: During the initial hypothermia MRI at 23.5±5.2 h after birth, infants with severe HIE had lower oxygen extraction fraction (P=0.04) and cerebral metabolic rate of oxygen (P=0.03) and a trend toward lower cerebral blood flow (P=0.33) compared to infants with moderate HIE. In infants with moderate HIE, cerebral blood flow decreased and oxygen extraction fraction increased between MRIs during and after hypothermia (although not significantly); cerebral metabolic rate of oxygen (P=0.93) was not different. CONCLUSION: Early MRIs were technically feasible while maintaining hypothermic goal temperatures in infants with HIE. Cerebral oxygen metabolism early during hypothermia is more disturbed in severe HIE. In infants with moderate HIE, cerebral blood flow decreased and oxygen extraction fraction increased between early and post-hypothermia scans. A comparison of cerebral oxygen metabolism parameters between early and post-hypothermia MRIs might improve our understanding of the evolution of HIE and the benefits of hypothermia. This approach could guide the use of adjunctive neuroprotective strategies in affected infants.

Improving spectral quality in fetal brain magnetic resonance spectroscopy using constructive averaging.

PURPOSE: A common source of loss in signal-to-noise ratio (SNR) in fetal brain magnetic resonance spectroscopy (MRS) is from fetal movement and temporal magnetic field drift. We investigated the feasibility of using constructive averaging strategies for improving the spectral quality and recovering the SNR loss from these effects. MATERIALS AND METHODS: Eight fetuses, between 20 3/7 and 38 2/7 weeks' gestation, were scanned with MRS at 1.5 T. Single-voxel point-resolved spectroscopy of the fetal brain with TE = 144 ms (in one case additional TE = 288 ms) was performed in a dynamic mode, and individual spectra of 128 acquisitions were saved. With constructive averaging strategy individual acquisitions were corrected for phase variations and frequency drift before averaging. Constructively averaged spectra were compared to those using conventional averaging to evaluate differences in spectral quality and SNR. RESULTS: The definition of key metabolite peaks was qualitatively improved using constructive averaging, including the doublet structure of lactate in one case. Constructive averaging was associated with SNR increases, ranging from 11% to 40%, and the SNR further improved in one case when outliers from severe motion were rejected before averaging. CONCLUSION: Our results demonstrate the feasibility of using constructive averaging for improving SNR in fetal MRS, which is likely to improve the characterization of fetal brain metabolites.

Contrast volume reduction with superior vena cava catheter-directed coronary CT angiography: comparison with peripheral i.v. contrast enhancement in a swine model.

OBJECTIVE: Conventional MDCT angiography uses a traditional peripheral i.v. approach for contrast injection; however, we describe our experience with a superior vena cava (SVC) catheter approach for coronary artery MDCT angiography as a potential means of decreasing iodinated contrast volume. CONCLUSION: Central SVC contrast injection can decrease the contrast volume by 50% while maintaining coronary attenuation similar to that of peripheral i.v. injection. This approach has potential in reducing the contrast volume on coronary MDCT angiography studies and therefore the risk of contrast-induced nephropathy in certain high-risk patients. Further studies with higher injection rates and faster scan acquisition are needed for defining a lower contrast volume threshold.

A liposomal Gd contrast agent does not cross the mouse placental barrier.

The trans-placental permeability of liposomal Gadolinium (Gd) nanoparticle contrast agents was evaluated in a pregnant mouse model. Pregnant Balb/c mice at 16.5 (±1) days of gestation were imaged using a 3D Spoiled Gradient Echo method at 9.4 T using two contrast agents: a clinically approved Gd chelate, Multihance(®) (gadobenate dimeglumine), and a novel experimental liposomal Gd agent. A Dynamic Contrast Enhancement (DCE) protocol was used to capture the dynamics of contrast entry and distribution in the placenta, and clearance from circulation. A blinded clinical radiologist evaluated both sets of images. A reference region model was used to measure the placental flow and physiological parameters; volume transfer constant (K(trans)), efflux rate constant (K(ep)). The Gd content of excised placentae and fetuses was measured, using inductively coupled plasma mass spectrometry (ICP-MS). MRI images of pregnant mice and ICP-MS analyses of placental and fetal tissue demonstrated undetectably low transplacental permeation of the liposomal Gd agent, while the clinical agent (Multihance) avidly permeated the placental barrier. Image interpretation and diagnostic quality was equivalent between the two contrast agents. Additional testing to determine both maternal and fetal safety of liposomal Gd is suggested.

Spatial Mapping of Translational Diffusion Coefficients Using Diffusion Tensor Imaging: A Mathematical Description.

In this article, we discuss the theoretical background for diffusion weighted imaging and diffusion tensor imaging. Molecular diffusion is a random process involving thermal Brownian motion. In biological tissues, the underlying microstructures restrict the diffusion of water molecules, making diffusion directionally dependent. Water diffusion in tissue is mathematically characterized by the diffusion tensor, the elements of which contain information about the magnitude and direction of diffusion and is a function of the coordinate system. Thus, it is possible to generate contrast in tissue based primarily on diffusion effects. Expressing diffusion in terms of the measured diffusion coefficient (eigenvalue) in any one direction can lead to errors. Nowhere is this more evident than in white matter, due to the preferential orientation of myelin fibers. The directional dependency is removed by diagonalization of the diffusion tensor, which then yields a set of three eigenvalues and eigenvectors, representing the magnitude and direction of the three orthogonal axes of the diffusion ellipsoid, respectively. For example, the eigenvalue corresponding to the eigenvector along the long axis of the fiber corresponds qualitatively to diffusion with least restriction. Determination of the principal values of the diffusion tensor and various anisotropic indices provides structural information. We review the use of diffusion measurements using the modified Stejskal-Tanner diffusion equation. The anisotropy is analyzed by decomposing the diffusion tensor based on symmetrical properties describing the geometry of diffusion tensor. We further describe diffusion tensor properties in visualizing fiber tract organization of the human brain.

Coronary 64-slice computed tomographic angiography models employing aortic root and selective catheter directed contrast enhancement in swine: technical feasibility and preliminary results using 3D and 4D reconstructions.

PURPOSE: The technical feasibility of combining catheter directed coronary enhancement and multidetector computed tomographic angiography (MD-CTA) is presented in a swine model at various cardiac and injection rates. MATERIALS/METHODS: A 64-slice CT scanner was used under animal IRB approval in four sedated swine. Common femoral venous/arterial access with a 5 Fr micropuncture kit was ultrasound guided. Investigational 5 Fr diffusion-tip pigtail [aortic root (AR)-MD-CTA] and conventional 5 Fr coronary [selective (S)-MD-CTA] catheters were positioned on the CT table with c-arm fluoroscopy. AR-MD-CTA commenced 1-2 s after injection of 50 cc Visipaque mixed with 50 cc NS at 6 cc/s (n=3), 8 cc/s (n=5) or 10 cc/s (n=7) (HR=120, 100, 90, 80 or 65 bpm). S-MD-CTA (right and left, n=4) (HR= 90, 80, or 65 bpm) commenced 1-2 s after injection of 5 cc Visipaque mixed with 5 cc NS (1 cc/s). IV-MD-CTA (n=4) (HR=80 bpm) commenced 5 or 10 s after aortic peak density with 100 cc Visipaque (5 cc/s) and 50 or 75 cc NS (5 cc/s) flush. Conventional angiography (n=2) used standard protocol. MD-CTA was performed with the following parameters: collimation 0.6 mm, tube rotation time 0.3 s, table feed/rotation 3.8 mm, scan time 10-12 s, tube voltage 120 kVp, effective mAs 850, pitch 0.2, FOV 109-123 mm, slice thickness/increment 0.6 mm/0.3 mm, kernel B25 f smooth. Ex vivo imaging (64-slice CT, n=3) was also performed. Post-processing consisted of coronary peak densities, 3D-MIP's and 4D projections. RESULTS: Catheter directed MD-CTA was feasible at all injection rates at and below 100 bpm and yielded higher peak coronary attenuation values than IV-enhanced studies. Definition and clarity of the tributary and distal anatomy was also higher than IV-enhanced CTA. CONCLUSIONS: Catheter directed MD-CTA can be performed by retrofitting the current CT scanner with a portable c-arm fluoroscopy unit. S and AR MD-CTA provide high coronary anatomy definition and luminal attenuation without obscuring cardiac chamber signal and with the least iodinated contrast volume.

Microvascular obstruction and myocardial function after acute myocardial infarction: assessment by using contrast-enhanced cine MR imaging.

UNLABELLED: This study was approved by the Human Investigation Committee of William Beaumont Hospital, and all patients gave informed consent. The purpose of this study was to prospectively compare contrast material-enhanced cine magnetic resonance (MR) imaging with more-standard MR imaging for the evaluation of microvascular obstruction and myocardial function in 80 patients (56 men, 24 women; mean age, 57 years; range, 29-80 years) with acute myocardial infarction after reperfusion therapy. Findings at contrast-enhanced cine MR imaging agreed with the global and transmural extent of microvascular obstruction at first-pass perfusion (intraclass correlation coefficient [IC] of 0.96 [P < .001] and 0.88 [P < .001], respectively) and inversion-recovery gradient-echo (IC of 0.90 [P < .001] and 0.93 [P < .001], respectively) MR imaging. There was no significant difference between myocardial function parameters before and after contrast material enhancement. Contrast-enhanced cine MR imaging reduced imaging time by 34% (11 of 32 minutes) and improved spatial resolution. SUPPLEMENTAL MATERIAL: radiology.rsnajnls.org/cgi/content/full/240/2/529/DC1

Catheter contrast-enhanced coronary CT-angiography using an aortic root injection--preliminary technical development in four patients.

The feasibility of performing coronary computed tomographic angiography (CTA) with an intra-aortic injection of iodinated contrast was tested in four patients immediately following diagnostic cardiac catheterization and placement of a 6-french pigtail catheter into the aortic root. A diluted contrast mixture [75 cc Omnipaque 350 mixed with 125 cc normal saline (4-slice scanner) vs. 40 cc Omnipaque 350 mixed with 60 cc normal saline (16-slice scanner)] was injected at a rate of 6 to 7.7 cc/sec at the onset of breath-hold and helical (4 slice, n=3, and 16-slice, n=1) retrospective ECG-triggered acquisition. The proximal and distal coronary vasculature including small tributaries were depicted with high signal-to-noise (S/N) and free from underlying blood pool enhancement. The right coronary artery was sub optimally enhanced in two patients. No significant disease was found on CTA or XRA in two patients; however, severe multivessel disease was demonstrated on both modalities in two patients. Catheter contrast-enhanced coronary CTA is feasible utilizing low injection rates and low iodinated contrast volumes, however, catheter modifications are required for consistent and homogeneous opacification of the aortic root.

Lower extremity MR angiography: universal retrofitting of high-field-strength systems with stepping kinematic imaging platforms initial experience.

In 15 volunteers and 84 patients with clinically suspected peripheral vascular disease, a stepping kinematic imaging platform, a manual retrofit stepping magnetic resonance (MR) imaging table, was used with three high-field-strength MR imaging systems to perform multistation peripheral contrast material-enhanced MR angiography in the lower extremity with the existing system phased-array coil. Each examination was performed in less than 45 minutes. Mounting of the stepping kinematic imaging platform was quick and simple and allowed rapid repositioning of a patient relative to the phased-array coil and acquisition of high-spatial-resolution MR angiograms of the peripheral vasculature with use of one injection of MR imaging contrast agent.

Contrast-enhanced three-dimensional MR angiography of the pulmonary vascular tree.

Contrast-enhanced three-dimensional MR angiography has evolved into a promising technique in the study of the pulmonary vasculature. Both congenital and acquired entities can be now morphologically demonstrated in a non-invasive manner obviating the need for conventional pulmonary angiography. Due to spatial resolution limitations, however, it is still premature to routinely apply the method in the detection of small subsegmental emboli, in cases of suspected pulmonary embolism, and further technical developments will be required. In this paper we present a spectrum of congenital and acquired disorders affecting the pulmonary vascular tree as demonstrated with contrast-enhanced three-dimensional MR angiography.