Biomedical subjects

Kenneth R Maravilla

Publications and source records attributed to Kenneth R Maravilla.

At least 19 recordsLinked to original sources

PubMed2006

Predictors of carotid atherosclerotic plaque progression as measured by noninvasive magnetic resonance imaging.

The purpose of this in vivo MRI study was to quantify changes in atherosclerotic plaque morphology prospectively and to identify factors that may alter the rate of progression in plaque burden. Sixty-eight asymptomatic subjects with >or=50% stenosis, underwent serial carotid MRI examinations over an 18-month period. Clinical risk factors for atherosclerosis, and medications were documented prospectively. The wall and total vessel areas, matched across time-points, were measured from cross-sectional images. The normalized wall index (NWI=wall area/total vessel area), as a marker of disease severity, was documented at baseline and at 18 months. Multiple regression analysis was used to correlate risk factors and morphological features of the plaque with the rate of progression/regression. On average, the wall area increased by 2.2% per year (P=0.001). Multiple regression analysis demonstrated that statin therapy (P=0.01) and a normalized wall index >0.64 (P=0.001) were associated with a significantly reduced rate of progression in mean wall area. All other documented risk factors were not significantly associated with changes in wall area. Findings from this study suggest that increased normalized wall index and the use of statin therapy are associated with reduced rates of plaque progression amongst individuals with advanced, asymptomatic carotid atherosclerosis.

Aged↗

PubMed2006

In vivo imaging of functional disruption, recovery and alteration in rat olfactory circuitry after lesion.

Compensatory changes following disruption of neuronal circuitry have been indicated by previous imaging studies of stroke and other brain injury, but evidence of the pathways involved in such dynamic changes has not been shown in vivo. We imaged rats before and after lesion-induced disruption of the lateral olfactory tract to investigate the subsequent recovery and/or reorganization of functional neuronal circuitry. Serial magnetic resonance imaging was performed following intranasal administration of a paramagnetic track tracer Mn(2+). Images were analyzed using statistical mapping techniques in the stereotactic coordinate system. At 1 week post-lesion, Mn(2+) transport caudal to lesion was reduced as expected, and more importantly, increased transport through the anterior commissure was seen. At 4 weeks post-lesion, there was recovery of transport caudal to lesion, and increased transport through the anterior commissure extended to the contralateral olfactory cortex. Correlation analysis of regional Mn(2+) transport indicated that contralateral enhancement was not simply due to septal window spillover. This study demonstrates for the first time in vivo evidence of compensatory changes in functional neuronal activity to a contralateral pathway through the commissure following brain injury.

Administration, Intranasal↗

PubMed2006

Contrast enhancement of central nervous system lesions: multicenter intraindividual crossover comparative study of two MR contrast agents.

PURPOSE: To prospectively compare gadobenate dimeglumine with gadopentetate dimeglumine (0.1 mmol per kilogram body weight) for enhanced magnetic resonance (MR) imaging of central nervous system (CNS) lesions. MATERIALS AND METHODS: This study was HIPAA-compliant at U.S. centers and was conducted at all centers according to the Good Clinical Practice standard. Institutional review board and regulatory approval were granted; written informed consent was obtained. Seventy-nine men and 78 women (mean age, 50.5 years +/- 14.4 [standard deviation]) were randomized to group A (n = 78) or B (n = 79). Patients underwent two temporally separated 1.5-T MR imaging examinations. In randomized order, gadobenate followed by gadopentetate was administered in group A; order of administration was reversed in group B. Contrast agent administration (volume, speed of injection), imaging parameters before and after injection, and time between injections and postinjection acquisitions were identical for both examinations. Three blinded neuroradiologists evaluated images by using objective image interpretation criteria for diagnostic information end points (lesion border delineation, definition of disease extent, visualization of internal morphologic features of the lesion, enhancement of the lesion) and quantitative parameters (percentage of lesion enhancement, contrast-to-noise ratio [CNR]). Overall diagnostic preference in terms of lesion conspicuity, detectability, and diagnostic confidence was assessed. Between-group comparisons were performed with Wilcoxon signed rank test. RESULTS: Readers 1, 2, and 3 demonstrated overall preference for gadobenate in 75, 89, and 103 patients, compared with that for gadopentetate in seven, 10, and six patients, respectively (P < .0001). Significant (P < .0001) preference for gadobenate was demonstrated for diagnostic information end points, percentage of lesion enhancement, and CNR. Superiority of gadobenate was significant (P < .001) in patients with intraaxial and extraaxial lesions. CONCLUSION: Gadobenate compared with gadopentetate at an equivalent dose provides significantly better enhancement and diagnostic information for CNS MR imaging.

Central Nervous System Diseases↗

PubMed2006

Low-frequency signal changes reflect differences in functional connectivity between good readers and dyslexics during continuous phoneme mapping.

The current fMRI study investigated correlations of low-frequency signal changes in the left inferior frontal gyrus, right inferior frontal gyrus and cerebellum in 13 adult dyslexic and 10 normal readers to examine functional networks associated with these regions. The extent of these networks to regions associated with phonological processing (frontal gyrus, occipital gyrus, angular gyrus, inferior temporal gyrus, fusiform gyrus, supramarginal gyrus and cerebellum) was compared between good and dyslexic readers. Analysis of correlations in low-frequency range showed that regions known to activate during an "on-off" phoneme-mapping task exhibit synchronous signal changes when the task is administered continuously (without any "off" periods). Results showed that three functional networks, which were defined on the basis of documented structural deficits in dyslexics and included regions associated with phonological processing, differed significantly in spatial extent between good readers and dyslexics. The methodological, theoretical and clinical significance of the findings for advancing fMRI research and knowledge of dyslexia are discussed.

Adult↗

PubMed2006

Association between carotid plaque characteristics and subsequent ischemic cerebrovascular events: a prospective assessment with MRI--initial results.

BACKGROUND AND PURPOSE: MRI is able to quantify carotid plaque size and composition with good accuracy and reproducibility and provides an opportunity to prospectively examine the relationship between plaque features and subsequent cerebrovascular events. We tested the hypothesis that the characteristics of carotid plaque, as assessed by MRI, are possible predictors of future ipsilateral cerebrovascular events. METHODS: A total of 154 consecutive subjects who initially had an asymptomatic 50% to 79% carotid stenosis by ultrasound with > or =12 months of follow-up were included in this study. Multicontrast-weighted carotid MRIs were performed at baseline, and participants were followed clinically every 3 months to identify symptoms of cerebrovascular events. RESULTS: Over a mean follow-up period of 38.2 months, 12 carotid cerebrovascular events occurred ipsilateral to the index carotid artery. Cox regression analysis demonstrated a significant association between baseline MRI identification of the following plaque characteristics and subsequent symptoms during follow-up: presence of a thin or ruptured fibrous cap (hazard ratio, 17.0; P< or =0.001), intraplaque hemorrhage (hazard ratio, 5.2; P=0.005), larger mean intraplaque hemorrhage area (hazard ratio for 10 mm2 increase, 2.6; P=0.006), larger maximum %lipid-rich/necrotic core (hazard ratio for 10% increase, 1.6; P=0.004), and larger maximum wall thickness (hazard ratio for a 1-mm increase, 1.6; P=0.008). CONCLUSIONS: Among patients who initially had an asymptomatic 50% to 79% carotid stenosis, arteries with thinned or ruptured fibrous caps, intraplaque hemorrhage, larger maximum %lipid-rich/necrotic cores, and larger maximum wall thickness by MRI were associated with the occurrence of subsequent cerebrovascular events. Findings from this prospective study provide a basis for larger multicenter studies to assess the risk of plaque features for subsequent ischemic events.

Aged↗

PubMed2006

Blood-brain barrier imaging and therapeutic potentials.

Much work has been done in the last several decades to improve the understanding of the molecular composition of the blood-brain barrier (BBB). Advances in magnetic resonance imaging have resulted in development of dynamic magnetic resonance imaging techniques to quantify permeability measurements across the brain endothelium. This review describes the basic anatomical and biochemical concepts of a BBB and the various techniques for magnetic resonance measurement of BBB permeability. To date, BBB permeability data have been shown to be useful in preoperative brain tumor grading and potentially also in determining the effectiveness of selective types of therapy. Explorative studies are evaluating new strategies for safe and effective altering of the BBB permeability to improve local drug delivery into brain tumors. As new antiangiogenesis drugs become available, BBB permeability imaging may also become critical as a surrogate angiogenesis marker to monitor tumor response to these agents. Finally, BBB permeability data may also prove useful in future applications to guide therapy in other nontumoral disease processes such as acute cerebral ischemia and inflammatory processes such as multiple sclerosis.

Blood-Brain Barrier↗

PubMed2006

Sexually responsive vascular tissue of the vulva.

OBJECTIVE: To better understand the genital changes that occur during the female sexual response, using a gross anatomical and histological study of the vascular tissue of the vulva, supplemented with magnetic resonance imaging (MRI). MATERIALS AND METHODS: Seven cadaveric vulvectomy specimens were used; they were serially sectioned in coronal, sagittal, and axial planes, and stained with haematoxylin and eosin. Selected blocks were stained with elastic Masson's trichrome. Axial MR images were taken of two healthy women with intact sexual functioning using a gadolinium-based blood-pool contrast agent. A 1.5 T system was used for all MRI studies, with images taken at baseline and during sexual arousal while viewing an erotic videotape. RESULTS: There are five vascular compartments of the female external genitalia, found in the clitoris, clitoral bulbs, labia minora, urethra, and vestibule/vagina. Of these five compartments, two distinct types of vascular tissue were identified, i.e. erectile and non-erectile/specialized genital. The erectile tissue compartments had the greatest change in blood volume during sexual arousal, as assessed by MRI. CONCLUSIONS: The vulva contains a substantial amount of vascular tissue. These specialized tissues show a variable, but unified response to sexual arousal.

Arousal↗

PubMed2005

Noncontrast dynamic magnetic resonance imaging for quantitative assessment of female sexual arousal.

PURPOSE: We evaluated a noncontrast, dynamic magnetic resonance imaging (MRI) technique for quantitative evaluation of the female sexual arousal response and compared these results with those of a previously described, contrast enhanced MRI technique. MATERIALS AND METHODS: Eight normal, healthy volunteer women underwent 2 separate MRI sessions, during which they were shown audiovisual material consisting of interleaved neutral and audiovisual sexual stimulation segments. Serial high resolution MRI of the genital structures was done at 3-minute intervals during a 45-minute period. Images were analyzed in blinded fashion and measurements of clitoral volume with time were obtained for each subject. Measured clitoral volumes together with the percent change in clitoral volume during audiovisual sexual stimulation for MRI sessions 1 and 2 were compared within subjects. Results were also compared to those of prior contrast enhanced MRI studies in the same subjects. RESULTS: There was excellent intrasubject reproducibility between sessions 1 and 2 using the noncontrast MRI technique (r = 0.99). There was also excellent agreement between the current noncontrast study and prior contrast enhanced studies with a correlation coefficient of 0.89. CONCLUSIONS: Dynamic, noncontrast MRI of the female genitalia appears to be a reproducible, nonintrusive and objective way to assess quantitatively the sexual arousal response in women without sexual difficulties.

Arousal↗

PubMed2004

MR neurography and muscle MR imaging for image diagnosis of disorders affecting the peripheral nerves and musculature.

Recent advances in the technology of MR imaging are beginning to transform the fundamental methodology of diagnostic evaluations in neuromuscular disorders. When properly implemented, MR neurography is capable of providing high-quality information about nerve compression, nerve inflammation, nerve trauma, systemic neuropathies, nerve tumors, and recovery of nerve from pathologic states. Muscle MR imaging can identify denervation on a precise anatomic basis, document the progression of various conditions causing myopathy and myositis; and even provide insight into abnormal patterns of muscle activation. There is an essential role for the neurologist as well as for the specialist radiologist that requires a high level of familiarity of the various new types of image findings in this steadily advancing field.

Humans↗

PubMed2004

Statistical mapping of functional olfactory connections of the rat brain in vivo.

The olfactory pathway is a unique route into the brain. To better characterize this system in vivo, rat olfactory functional connections were mapped using magnetic resonance (MR) imaging and manganese ion (Mn2+) as a transport-mediated tracer combined with newly developed statistical brain image analysis. Six rats underwent imaging on a 1.5-T MR scanner at pre-administration, and 6, 12, 24, 36, 48, and 72 h and 5.5, 7.5, 10.5, and 13.5 days post-administration of manganese chloride (MnCl2) into the right nasal cavity. Images were coregistered, pixel-intensity normalized, and stereotactically transformed to the Paxinos and Watson rat brain atlas, then averaged across subjects using automated image analysis software (NEUROSTAT). Images at each time point were compared to pre-administration using a one-sample t statistic on a pixel-by-pixel basis in 3-D and converted to Z statistic maps. Statistical mapping and group averaging improved signal to noise ratios and signal detection sensitivity. Significant transport of Mn2+ was observed in olfactory structures ipsilateral to site of Mn2+ administration including the bulb, lateral olfactory tract (lo) by 12 h and in the tubercle, piriform cortex, ventral pallidum, amygdala, and in smaller structures such as the anterior commissure after 24 h post-administration. MR imaging with group-wise statistical analysis clearly demonstrated bilateral transsynaptic Mn2+ transport to secondary and tertiary neurons of the olfactory system. The method permits in vivo investigations of functional neuronal connections within the brain.

Amygdala↗

PubMed2004

The brachial plexus: normal anatomy, pathology, and MR imaging.

The brachial plexus is the most technically and anatomically challenging area of the peripheral nervous system for diagnostic imaging. Marked improvements in spatial and contrast resolution of plexus images have resulted from the use of phased-array technology and newer MR pulse sequence designs. This article presents case material incorporating these improvements and discusses the primary factors that continue to limit MR image quality, such as inhomogenous fat suppression, motion artifacts, and small vessels that mimic or obscure plexus components, and potential solutions and imaging alternatives. Brachial plexus anatomy and its appearance on multiplanar MR images are reviewed. The morphologic features and MR signal characteristics that have been found useful in distinguishing between normal and abnormal plexus components,and in detecting neuropathic lesions, are addressed in the context of clinical indications for plexus imaging as follows: mass involving the plexus, traumatic injury, entrapment syndrome, posttreatment evaluation, and miscellaneous conditions.

Animals↗

PubMed2004

MR neurography: diagnostic utility in the surgical treatment of peripheral nerve disorders.

Advances in MR imaging have improved the visualization of normal and pathologic peripheral nerve structures in various clinical settings. Peripheral nerve imaging has the potential to dramatically change the diagnosis and treatment of peripheral nerve pathology and lead to an improved understanding of peripheral nerve pathophysiology. Currently, MR imaging serves as a problem-solving tool when additional anatomic information is needed to clarify ambiguous electrodiagnostic and clinical examinations. The next major advance in MR imaging of peripheral nerves will likely be the transition from anatomic to physiologic imaging with higher resolution as better phased-array surface coils and higher-field-strength magnets become available. Finally, MR neurography should remain complementary to the clinical examination and electrodiagnostic studies in the evaluation of peripheral nerve disorders.

Electrodiagnosis↗

PubMed2004

Paramagnetic effect of supplemental oxygen on CSF hyperintensity on fluid-attenuated inversion recovery MR images.

BACKGROUND AND PURPOSE: Oxygen has a known paramagnetic effect and increases CSF signal intensity on fluid-attenuated inversion recovery (FLAIR) MR images. The purposes of this study were to investigate the effect of supplemental oxygen on CSF signal intensity and the arterial partial pressure of oxygen and to determine the possible synergistic effect of oxygen and albumin on T1 shortening effect in vitro. METHODS: Six healthy volunteers underwent FLAIR MR imaging of the brain before and during inhalation of 10 to 15 L/min of 100% oxygen for < or = 30 min. The signal intensity was measured in the subarachnoid spaces and various tissues and correlated with estimated arterial partial pressure of oxygen and arterial carbon dioxide pressure. In vitro measurements were also obtained by using two sets of saline-filled tubes with various concentrations of albumin, one of which was exposed to increased oxygen levels. In vitro T1 relaxation times were calculated to assess the possible synergistic effect of oxygen and albumin. RESULTS: FLAIR images of healthy volunteers showed increased CSF signal intensity within the basal cisterns and sulci along the cerebral convexities. The CSF hyperintensity was observed immediately after the initiation of supplemental oxygen and remained stable during the oxygen administration. There was approximately a 4- to 5.3-fold increase in signal intensity with supplemental oxygen. The phantom experiments showed a T1 shortening effect of oxygen. Albumin significantly altered T1 relaxation time only at high concentrations of albumin. CONCLUSION: Inhalation of increased levels of oxygen led to readily detectable CSF hyperintensity on FLAIR images of healthy volunteers. No significant synergetic effect of albumin and oxygen was noted.

Administration, Inhalation↗

PubMed2003

High-dose immunosuppressive therapy and autologous peripheral blood stem cell transplantation for severe multiple sclerosis.

There were 26 patients enrolled in a pilot study of high-dose immunosuppressive therapy (HDIT) for severe multiple sclerosis (MS). Median baseline expanded disability status scale (EDSS) was 7.0 (range, 5.0-8.0). HDIT consisted of total body irradiation, cyclophosphamide, and antithymocyte globulin (ATG) and was followed by transplantation of autologous, granulocyte colony-stimulating factor (G-CSF)-mobilized CD34-selected stem cells. Regimen-related toxicities were mild. Because of bladder dysfunction, there were 8 infectious events of the lower urinary tract. One patient died from Epstein-Barr virus (EBV)-related posttransplantation lymphoproliferative disorder (PTLD) associated with a change from horse-derived to rabbit-derived ATG in the HDIT regimen. An engraftment syndrome characterized by noninfectious fever with or without rash developed in 13 of the first 18 patients and was associated in some cases with transient worsening of neurologic symptoms. There were 2 significant adverse neurologic events that occurred, including a flare of MS during mobilization and an episode of irreversible neurologic deterioration after HDIT associated with fever. With a median follow-up of 24 (range, 3-36) months, the Kaplan-Meier estimate of progression (>/= 1.0 point EDSS) at 3 years was 27%. Of 12 patients who had oligoclonal bands in the cerebrospinal fluid at baseline, 9 had persistence after HDIT. After HDIT, 4 patients developed new enhancing lesions on magnetic resonance imaging of the brain. The estimate of survival at 3 years was 91%. Important clinical issues in the use of HDIT and stem cell transplantation for MS were identified; however, modifications of the initial approaches appear to reduce treatment risks. This was a heterogeneous high-risk group, and a phase 3 study is planned to fully assess efficacy.

Adult↗

PubMed2003

Serial MR imaging with MS-325 for evaluating female sexual arousal response: determination of intrasubject reproducibility.

PURPOSE: To determine if a similar sexual arousal response in normal, healthy women could be obtained and monitored by serial magnetic resonance (MR) imaging at two separate sessions. MATERIALS AND METHODS: Serial imaging of the external genitalia was performed on nine healthy, sexually functional women at two separate MR sessions after administration of the contrast agent, MS-325. Images were obtained every three minutes during a 45-minute study period during each MR session. The second MR session began approximately 45 minutes after the end of the first MR session. While undergoing imaging, subjects viewed videotapes that contained neutral and sexually-explicit material through an audiovisual system. Analysis performed at each time point consisted of visual evaluation of the images, clitoral and femoral vein signal intensity measurements, relative regional blood volume calculations, and clitoral volume measurements. Statistical analysis of the results consisted of calculating correlation coefficients of the two MR sessions by using the least square fit method. RESULTS: All nine subjects reported sexual arousal on subjective questionnaires at each MR session. Post-contrast MS-325 MR images showed strong enhancement of the external genitalia at each session. There was excellent correlation between the two sessions for the clitoral volume measurements of all nine subjects. The correlation coefficient, r(2), was 0.95. CONCLUSION: The sexual arousal response in normal, healthy women can be monitored by serial imaging combined with the use of the contrast agent, MS-325, and similar results can be reproduced at two different MR sessions. This method holds promise for future studies of women with female sexual arousal dysfunction.

Adult↗

PubMed2003

FMRI investigation of cross-cultural music comprehension.

The popular view of music as a "universal" language ignores the privileged position of the cultural insider in comprehending musical information unique to their own tradition. The purpose of this study was to test the hypothesis that listeners would demonstrate different neural activity in response to culturally familiar and unfamiliar music and that those differences may be affected by the extent of subjects' formal musical training. Just as familiar languages have been shown to use distinct brain processes, we hypothesized that an analogous difference might be found in music and that it may depend in part on subjects' formal musical knowledge. Using fMRI we compared the activation patterns of professional musicians and untrained controls reared in the United States as they listened to music from their culture (Western) and from an unfamiliar culture (Chinese). No overall differences in activation were observed for either subject group in response to the two musical styles, although there were differences in recall performance based on style and there were activation differences based on training. Trained listeners demonstrated additional activation in the right STG for both musics and in the right and left midfrontal regions for Western music and Chinese music, respectively. Our findings indicate that listening to culturally different musics may activate similar neural resources but with dissimilar results in recall performance.

Acoustic Stimulation↗

PubMed2003

Dynamic MR imaging of the sexual arousal response in women.

The purpose of our studies was to evaluate whether MR imaging could be used to noninvasively observe and measure the sexual arousal response in normal women. We tested the feasibility as well as the reproducibility of rapid, dynamic, serial high-resolution MR imaging of the genital structures during presentation of neutral and sexually stimulating video material. Results show that these MRI techniques can visualize significant changes in clitoral volume during the stimulus segment of the video presentation. Quantitative measurements made of these changes were robust and reproducible. These studies suggest that MRI techniques may be a useful tool to improve our understanding of the physiology involved with the sexual arousal response in women. These MRI techniques may also prove useful as a surrogate end point marker for testing efficacy of future new treatments for women with sexual arousal disorder.

Adult↗

PubMed2003

Magnetic resonance imaging anatomy of the female genitalia in premenopausal and postmenopausal women.

PURPOSE: We used contrast enhanced magnetic resonance imaging (MRI) of the female genital organs to describe normal anatomy and differences between premenopausal and postmenopausal women. MATERIALS AND METHODS: A total of 12 healthy premenopausal and 9 healthy postmenopausal women underwent MRI. A 1.5 Tesla system with phased array coils anterior and posterior to the pelvis was used to produce T1-weighted images before and after intravenous administration of MS-325 (Epix Medical, Cambridge, Massachusetts), a new gadolinium based blood pool contrast agent. Select structural dimensions were measured for reference. RESULTS: The clitoris and vestibular bulbs were well delineated on T1-weighted post-contrast images. The clitoral unit formed a brightly enhancing, wishbone-shaped structure lying just anterior to the inverted V of the bulbs, which surrounded the urethra and vagina. The urethral complex had a target-like appearance with layers that were discernible on T1 post-contrast images. The urethra, vagina and rectum formed a distinct complex within uniformly enhancing soft tissue. The vagina was well visualized in premenopausal subjects but without distinguishable mucosal rugae or clearly separate layers in postmenopausal subjects. Postmenopausal subjects were also observed to have smaller labia minora width, vestibular bulb width, vaginal width and wall thickness, and cervical diameter. Pelvic and genital structures were not well visualized on T1 noncontrast images. CONCLUSIONS: To our knowledge we describe detailed female genital anatomy for the first time using MRI with MS-325 contrast medium. The clitoris, vestibular bulbs, labia majora and minora, urethra, vagina, cervix and rectum are well visualized on T1 post-contrast images. The observed genital anatomy on MRI was consistent with descriptions in current anatomical texts. Differences in the female genitalia between premenopausal and postmenopausal women were discernible on MRI. These data are important for future studies using MRI for evaluating anatomical anomalies, postoperative changes and female sexual function.

Adult↗