Assessment of splanchnic blood flow using magnetic resonance imaging

BACKGROUND AND AIMS: The splanchnic circulation has an important function in the body under both physiological and pathophysiological conditions. Despite its importance, no reliable noninvasive procedures for estimating splanchnic circulation have been established. The aim of this study was to evaluate MRI as a tool for assessing intra-abdominal blood flows of the aorta, portal vein (VPO) and the major intestinal and hepatic vessels. METHODS: In nine healthy volunteers, the proximal aorta (AOP) and distal abdominal aorta (AOD), superior mesenteric artery (SAM), celiac trunk (CTR), hepatic arteries (common and proper hepatic arteries, AHC and AHP, respectively), and VPO were localized on contrast-enhanced magnetic resonance angiography images. Volumetric flow was measured using a two-dimensional cine echocardiogram-gated phase contrast technique. Measurements were taken before and 30 min after continuous intravenous infusion of somatostatin (250 microg/h) and were independently evaluated by two investigators. RESULTS: Blood flow measured by MRI in the VPO, SAM, AOP, AHP, and CTR significantly decreased after drug infusion. Flows in the AOD and AHC showed a tendency to decrease (P>0.05). Interrater agreement on flows in MRI was very good for large vessels (VPO, AOP, and AOD), with a concordance correlation coefficient of 0.94, as well as for smaller vessels such as the CTR, AHC, AHP, and SAM (concordance correlation coefficient =0.78). CONCLUSION: Somatostatin-induced blood flow changes in the splanchnic region were reliably detected by MRI. MRI may be useful for the noninvasive assessment of blood flow changes in the splanchnic region.

Magnetic resonance imaging anatomy of the normal equine larynx and pharynx

The purpose of the present study was to describe normal magnetic resonance (MR) imaging anatomy of the equine larynx and pharynx and to present the optimal protocol, sequences, and possible limitations of this examination technique. Using a 0.3 T unit, the laryngeal and pharyngeal regions was imaged in two horses. The protocol consisted of sagittal and transverse T2-weighted (T2w) fast spin echo, transverse T1-weighted (T1w) spin echo, and dorsal high-resolution T1w gradient echo (both pre- and postcontrast enhancement) sequences. Euthanasia was performed at the end of the imaging procedure. Macroscopic anatomy of the cadaver sections were compared with the MR images in transverse, midsagittal, and parasagittal planes. There was good differentiation of anatomic structures, including soft tissues. The laryngeal cartilages, hyoid apparatus, and upper airway muscle groups with their attachments could be clearly identified. However, it was not always possible to delineate individual muscles in each plane. Most useful were both T2w and T1w transverse sequences. Intravenous application of contrast medium was helpful to identify blood vessels. The MR images corresponded with the macroscopic anatomy of cadaver sections.

Linking brain connectivity across different time scales with electroencephalogram, functional magnetic resonance imaging, and diffusion tensor imaging

Structural and functional connectivity are intrinsic properties of the human brain and represent the amount of cognitive capacities of individual subjects. These connections are modulated due to development, learning, and disease. Momentary adaptations in functional connectivity alter the structural connections, which in turn affect the functional connectivity. Thus, structural and functional connectivity interact on a broad timescale. In this study, we aimed to explore distinct measures of connectivity assessed by functional magnetic resonance imaging and diffusion tensor imaging and their association to the dominant electroencephalogram oscillatory property at rest: the individual alpha frequency (IAF). We found that in 21 healthy young subjects, small intraindividual temporal IAF fluctuations were correlated to increased blood oxygenation level-dependent signal in brain areas associated to working memory functions and to the modulation of attention. These areas colocalized with functionally connected networks supporting the respective functions. Furthermore, subjects with higher IAF show increased fractional anisotropy values in fascicles connecting the above-mentioned areas and networks. Hence, due to a multimodal approach a consistent functionally and structurally connected network related to IAF was observed.

Magnetic resonance imaging findings in dogs with traumatic intervertebral disk extrusion with or without spinal cord compression: 31 cases (2006-2010)

OBJECTIVE To determine the prevalence of spinal cord compression subsequent to traumatic intervertebral disk (IVD) extrusion in dogs, characterize factors associated with spinal cord compression in dogs with traumatic IVD extrusion, and evaluate the outcomes of dogs with traumatic IVD extrusion with or without spinal cord compression. DESIGN Retrospective case series. ANIMALS 31 dogs with traumatic IVD extrusion. PROCEDURES Medical records and MRI findings were reviewed for dogs with a history of trauma to the spinal region. Dogs were included in the study if a neurologic examination and MRI were performed and there was a description of clinical signs and MRI findings including identification of the spinal cord segment affected by IVD extrusion, presence or absence of spinal cord compression, treatment, and outcome available for review. RESULTS 31 of 50 (62%) dogs had traumatic IVD extrusions without any other detectable vertebral lesions; 9 (29%) and 22 (71%) of those 31 dogs did and did not have spinal cord compression, respectively. Dogs with spinal cord compression were significantly older and more likely to be chondrodystrophic and have evidence of generalized IVD degeneration, compared with dogs without spinal cord compression. The outcome for dogs with spinal cord compression was similar to that for dogs without spinal cord compression. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated traumatic IVD extrusion was common and should be considered as a differential diagnosis for dogs with trauma to the spinal region, and spinal cord compression should be evaluated, especially in older or chondrodystrophic dogs.

Catch-up alveolarization in ex-preterm children: evidence from (3)He magnetic resonance

RATIONALE Histologic data from fatal cases suggest that extreme prematurity results in persisting alveolar damage. However, there is new evidence that human alveolarization might continue throughout childhood and could contribute to alveolar repair. OBJECTIVES To examine whether alveolar damage in extreme-preterm survivors persists into late childhood, we compared alveolar dimensions between schoolchildren born term and preterm, using hyperpolarized helium-3 magnetic resonance. METHODS We recruited schoolchildren aged 10-14 years stratified by gestational age at birth (weeks) to four groups: (1) term-born (37-42 wk; n = 61); (2) mild preterm (32-36 wk; n = 21); (3) extreme preterm (<32 wk, not oxygen dependent at 4 wk; n = 19); and (4) extreme preterm with chronic lung disease (<32 wk and oxygen dependent beyond 4 wk; n = 18). We measured lung function using spirometry and plethysmography. Apparent diffusion coefficient, a surrogate for average alveolar dimensions, was measured by helium-3 magnetic resonance. MEASUREMENTS AND MAIN RESULTS The two extreme preterm groups had a lower FEV1 (P = 0.017) compared with term-born and mild preterm children. Apparent diffusion coefficient was 0.092 cm(2)/second (95% confidence interval, 0.089-0.095) in the term group. Corresponding values were 0.096 (0.091-0.101), 0.090 (0085-0.095), and 0.089 (0.083-0.094) in the mild preterm and two extreme preterm groups, respectively, implying comparable alveolar dimensions across all groups. Results did not change after controlling for anthropometric variables and potential confounders. CONCLUSIONS Alveolar size at school age was similar in survivors of extreme prematurity and term-born children. Because extreme preterm birth is associated with deranged alveolar structure in infancy, the most likely explanation for our finding is catch-up alveolarization.

Inverse relationship between fractionated electrograms and atrial fibrosis in persistent atrial fibrillation: combined magnetic resonance imaging and high-density mapping

OBJECTIVES This study sought to evaluate the relationship between fibrosis imaged by delayed-enhancement (DE) magnetic resonance imaging (MRI) and atrial electrograms (Egms) in persistent atrial fibrillation (AF). BACKGROUND Atrial fractionated Egms are strongly related to slow anisotropic conduction. Their relationship to atrial fibrosis has not yet been investigated. METHODS Atrial high-resolution MRI of 18 patients with persistent AF (11 long-lasting persistent AF) was registered with mapping geometry (NavX electro-anatomical system (version 8.0, St. Jude Medical, St. Paul, Minnesota)). DE areas were categorized as dense or patchy, depending on their DE content. Left atrial Egms during AF were acquired using a high-density, 20-pole catheter (514 ± 77 sites/map). Fractionation, organization/regularity, local mean cycle length (CL), and voltage were analyzed with regard to DE. RESULTS Patients with long-lasting persistent versus persistent AF had larger left atrial (LA) surface area (134 ± 38 cm(2) vs. 98 ± 9 cm(2), p = 0.02), a higher amount of atrial DE (70 ± 16 cm(2) vs. 49 ± 10 cm(2), p = 0.01), more complex fractionated atrial Egm (CFAE) extent (54 ± 16 cm(2) vs. 28 ± 15 cm(2), p = 0.02), and a shorter baseline AF CL (147 ± 10 ms vs. 182 ± 14 ms, p = 0.01). Continuous CFAE (CFEmean [NavX algorithm that quantifies Egm fractionation] <80 ms) occupied 38 ± 19% of total LA surface area. Dense DE was detected at the left posterior left atrium. In contrast, the right posterior left atrium contained predominantly patchy DE. Most CFAE (48 ± 14%) occurred at non-DE LA sites, followed by 41 ± 12% CFAE at patchy DE and 11 ± 6% at dense DE regions (p = 0.005 and p = 0.008, respectively); 19 ± 6% CFAE sites occurred at border zones of dense DE. Egms were less fractionated, with longer CL and lower voltage at dense DE versus non-DE regions: CFEmean: 97 ms versus 76 ms, p < 0.0001; local CL: 153 ms versus 143 ms, p < 0.0001; mean voltage: 0.63 mV versus 0.86 mV, p < 0.0001. CONCLUSIONS Atrial fibrosis as defined by DE MRI is associated with slower and more organized electrical activity but with lower voltage than healthy atrial areas. Ninety percent of continuous CFAE sites occur at non-DE and patchy DE LA sites. These findings are important when choosing the ablation strategy in persistent AF.

Integration of merged delayed-enhanced magnetic resonance imaging and multidetector computed tomography for the guidance of ventricular tachycardia ablation: a pilot study

BACKGROUND Delayed enhancement (DE) MRI can assess the fibrotic substrate of scar-related VT. MDCT has the advantage of inframillimetric spatial resolution and better 3D reconstructions. We sought to evaluate the feasibility and usefulness of integrating merged MDCT/MRI data in 3D-mapping systems for structure-function assessment and multimodal guidance of VT mapping and ablation. METHODS Nine patients, including 3 ischemic cardiomyopathy (ICM), 3 nonischemic cardiomyopathy (NICM), 2 myocarditis, and 1 redo procedure for idiopathic VT, underwent MRI and MDCT before VT ablation. Merged MRI/MDCT data were integrated in 3D-mapping systems and registered to high-density endocardial and epicardial maps. Low-voltage areas (<1.5 mV) and local abnormal ventricular activities (LAVA) during sinus rhythm were correlated to DE at MRI, and wall-thinning (WT) at MDCT. RESULTS Endocardium and epicardium were mapped with 391 ± 388 and 1098 ± 734 points per map, respectively. Registration of MDCT allowed visualization of coronary arteries during epicardial mapping/ablation. In the idiopathic patient, integration of MRI data identified previously ablated regions. In ICM patients, both DE at MRI and WT at MDCT matched areas of low voltage (overlap 94 ± 6% and 79 ± 5%, respectively). In NICM patients, wall-thinning areas matched areas of low voltage (overlap 63 ± 21%). In patients with myocarditis, subepicardial DE matched areas of epicardial low voltage (overlap 92 ± 12%). A total number of 266 LAVA sites were found in 7/9 patients. All LAVA sites were associated to structural substrate at imaging (90% inside, 100% within 18 mm). CONCLUSION The integration of merged MDCT and DEMRI data is feasible and allows combining substrate assessment with high-spatial resolution to better define structure-function relationship in scar-related VT.

Combined Ultrasmall Superparamagnetic Particles of Iron Oxide–Enhanced and Diffusion-weighted Magnetic Resonance Imaging Facilitates Detection of Metastases in Normal-sized Pelvic Lymph Nodes of Patients with Bladder and Prostate Cancer

Background Conventional cross-sectional imaging with computed tomography and magnetic resonance imaging (MRI) has limited accuracy for lymph node (LN) staging in bladder and prostate cancer patients. Objective To prospectively assess the diagnostic accuracy of combined ultrasmall superparamagnetic particles of iron oxide (USPIO) MRI and diffusion-weighted (DW) MRI in staging of normal-sized pelvic LNs in bladder and/or prostate cancer patients. Design, setting, and participants Examinations with 3-Tesla MRI 24–36 h after administration of USPIO using conventional MRI sequences combined with DW-MRI (USPIO-DW-MRI) were performed in 75 patients with clinically localised bladder and/or prostate cancer staged previously as N0 by conventional cross-sectional imaging. Combined USPIO-DW-MRI findings were analysed by three independent readers and correlated with histopathologic LN findings after extended pelvic LN dissection (PLND) and resection of primary tumours. Outcome measurements and statistical analysis Sensitivity and specificity for LN status of combined USPIO-DW-MRI versus histopathologic findings were evaluated per patient (primary end point) and per pelvic side (secondary end point). Time required for combined USPIO-DW-MRI reading was assessed. Results and limitations At histopathologic analysis, 2993 LNs (median: 39 LNs; range: 17–68 LNs per patient) with 54 LN metastases (1.8%) were found in 20 of 75 (27%) patients. Per-patient sensitivity and specificity for detection of LN metastases by the three readers ranged from 65% to 75% and 93% to 96%, respectively; sensitivity and specificity per pelvic side ranged from 58% to 67% and 94% to 97%, respectively. Median reading time for the combined USPIO-DW-MRI images was 9 min (range: 3–26 min). A potential limitation is the absence of a node-to-node correlation of combined USPIO-DW-MRI and histopathologic analysis. Conclusions Combined USPIO-DW-MRI improves detection of metastases in normal-sized pelvic LNs of bladder and/or prostate cancer patients in a short reading time.

On the use of Cramér-Rao minimum variance bounds for the design of magnetic resonance spectroscopy experiments

Localized Magnetic Resonance Spectroscopy (MRS) is in widespread use for clinical brain research. Standard acquisition sequences to obtain one-dimensional spectra suffer from substantial overlap of spectral contributions from many metabolites. Therefore, specially tuned editing sequences or two-dimensional acquisition schemes are applied to extend the information content. Tuning specific acquisition parameters allows to make the sequences more efficient or more specific for certain target metabolites. Cramér-Rao bounds have been used in other fields for optimization of experiments and are now shown to be very useful as design criteria for localized MRS sequence optimization. The principle is illustrated for one- and two-dimensional MRS, in particular the 2D separation experiment, where the usual restriction to equidistant echo time spacings and equal acquisition times per echo time can be abolished. Particular emphasis is placed on optimizing experiments for quantification of GABA and glutamate. The basic principles are verified by Monte Carlo simulations and in vivo for repeated acquisitions of generalized two-dimensional separation brain spectra obtained from healthy subjects and expanded by bootstrapping for better definition of the quantification uncertainties.

Magnetic resonance imaging and genetic investigation of a case of Rottweiler leukoencephalomyelopathy.

BACKGROUND Leukoencephalomyelopathy is an inherited neurodegenerative disorder that affects the white matter of the spinal cord and brain and is known to occur in the Rottweiler breed. Due to the lack of a genetic test for this disorder, post mortem neuropathological examinations are required to confirm the diagnosis. Leukoencephalopathy with brain stem and spinal cord involvement and elevated lactate levels is a rare, autosomal recessive disorder in humans that was recently described to have clinical features and magnetic resonance imaging (MRI) findings that are similar to the histopathologic lesions that define leukoencephalomyelopathy in Rottweilers. Leukoencephalopathy with brain stem and spinal cord involvement is caused by mutations in the DARS2 gene, which encodes a mitochondrial aspartyl-tRNA synthetase. The objective of this case report is to present the results of MRI and candidate gene analysis of a case of Rottweiler leukoencephalomyelopathy to investigate the hypothesis that leukoencephalomyelopathy in Rottweilers could serve as an animal model of human leukoencephalopathy with brain stem and spinal cord involvement. CASE PRESENTATION A two-and-a-half-year-old male purebred Rottweiler was evaluated for generalised progressive ataxia with hypermetria that was most evident in the thoracic limbs. MRI (T2-weighted) demonstrated well-circumscribed hyperintense signals within both lateral funiculi that extended from the level of the first to the sixth cervical vertebral body. A neurodegenerative disorder was suspected based on the progressive clinical course and MRI findings, and Rottweiler leukoencephalomyelopathy was subsequently confirmed via histopathology. The DARS2 gene was investigated as a causative candidate, but a sequence analysis failed to identify any disease-associated variants in the DNA sequence. CONCLUSION It was concluded that MRI may aid in the pre-mortem diagnosis of suspected cases of leukoencephalomyelopathy. Genes other than DARS2 may be involved in Rottweiler leukoencephalomyelopathy and may also be relevant in human leukoencephalopathy with brain stem and spinal cord involvement.

Quantitative 1H-magnetic resonance spectroscopy of human brain: Influence of composition and parameterization of the basis set in linear combination model-fitting

Localized short-echo-time (1)H-MR spectra of human brain contain contributions of many low-molecular-weight metabolites and baseline contributions of macromolecules. Two approaches to model such spectra are compared and the data acquisition sequence, optimized for reproducibility, is presented. Modeling relies on prior knowledge constraints and linear combination of metabolite spectra. Investigated was what can be gained by basis parameterization, i.e., description of basis spectra as sums of parametric lineshapes. Effects of basis composition and addition of experimentally measured macromolecular baselines were investigated also. Both fitting methods yielded quantitatively similar values, model deviations, error estimates, and reproducibility in the evaluation of 64 spectra of human gray and white matter from 40 subjects. Major advantages of parameterized basis functions are the possibilities to evaluate fitting parameters separately, to treat subgroup spectra as independent moieties, and to incorporate deviations from straightforward metabolite models. It was found that most of the 22 basis metabolites used may provide meaningful data when comparing patient cohorts. In individual spectra, sums of closely related metabolites are often more meaningful. Inclusion of a macromolecular basis component leads to relatively small, but significantly different tissue content for most metabolites. It provides a means to quantitate baseline contributions that may contain crucial clinical information.