Separating binding and retrieval of event files in older adults

In the literature on human action control, it is assumed that features of stimuli (S) and responses (R) are integrated into internal representations (so-called event files) that are involved in the execution of an action. Experimentally, the impact of this integration on action control is typically analyzed via S-R binding effects. Recent theorizing in the BRAC framework (Frings et al., 2020) suggests to disentangle the processes of S-R binding proper from S-R retrieval as two independent components contributing to S-R binding effects. Since the literature on age effects on S-R binding effects is scarce and does not provide information on whether the existing findings about the two processes can be generalized to older age groups, this is the first study addressing the effects of older age separately on S-R binding proper vs. S-R retrieval. In two established variants of S-R binding tasks (cumulative n = 262), we contrasted binding (by using a saliency manipulation at the time of binding proper) versus retrieval processes (by manipulating the onset of the distractor at the time of retrieval), replicating previous results in younger (18-30 years) and also in older healthy controls (50-70 years). We therefore found no evidence for age effects on S-R binding proper or S-R retrieval. We thus conclude that the processes contributing to S-R binding effects are - at least in the age groups analyzed in this study - robust and age-independent. STATEMENT OF SIGNIFICANCE: In human action control, binding proper and retrieval of features in stimulus-response episodes typically lead to so-called S-R binding effects. Against the background of recent theorizing, binding proper and retrieval should be studied independently. In this article, we ran a younger and an older age group and analyzed possible age-related differences in integration or retrieval. Both groups showed the expected pattern for binding and retrieval as expected from the literature.

Multisensory integration reduces landmark distortions for tactile but not visual targets

Target localization is influenced by the presence of additionally presented nontargets, termed landmarks. In both the visual and tactile modality, these landmarks led to systematic distortions of target localizations often resulting in a shift toward the landmark. This shift has been attributed to averaging the spatial memory of both stimuli. Crucially, everyday experiences often rely on multiple modalities, and multisensory research suggests that inputs from different senses are optimally integrated, not averaged, for accurate perception, resulting in more reliable perception of cross-modal compared with uni-modal stimuli. As this could also lead to a reduced influence of the landmark, we wanted to test whether landmark distortions would be reduced when presented in a different modality or whether landmark distortions were unaffected by the modalities presented. In two experiments (each n = 30) tactile or visual targets were paired with tactile or visual landmarks. Experiment 1 showed that targets were less shifted toward landmarks from the different than the same modality, which was more pronounced for tactile than for visual targets. Experiment 2 aimed to replicate this pattern with increased visual uncertainty to rule out that smaller localization shifts of visual targets due to low uncertainty had led to the results. Still, landmark modality influenced localization shifts for tactile but not visual targets. The data pattern for tactile targets is not in line with memory averaging but seems to reflect the effects of multisensory integration, whereas visual targets were less prone to landmark distortions and do not appear to benefit from multisensory integration.NEW & NOTEWORTHY In the present study, we directly tested the predictions of two different accounts, namely, spatial memory averaging and multisensory integration, concerning the degree of landmark distortions of targets across modalities. We showed that landmark distortions were reduced across modalities compared to distortions within modalities, which is in line with multisensory integration. Crucially, this pattern was more pronounced for tactile than for visual targets.

Increased display complexity reveals effects of salience in action control

In action-control research, typically, stimulus sparse displays are used. This might be one reason why previous theorizing focuses on the (top-down) demands of response selection (e.g., what key to press), while often ignoring (bottom-up) demands of stimulus selection (e.g., what stimulus to attend). However, complex perceptual situations may pose selection demands that make additional, response-unrelated feature dimensions relevant for response selection. The major stimulus characteristic affecting perceptual selection is salience. In research on visual attention, there is a debate about the conditions under which salience becomes effective. We related both debates in two experiments, in which we modulated display set size as well as salience in a stimulus-response binding task. In sum, the data of these experiments (pooled N = 138) demonstrated that salience furthered the integration of stimulus features in displays with many stimuli more than in sparse displays. Our results demonstrate the neglected impact of salience on action-control when going beyond the very simplistic displays common in action-control research. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Temporal expectancy modulates stimulus-response integration

We can use information derived from passing time to anticipate an upcoming event. If time before an event varies, responses towards this event become faster with increasing waiting time. This variable-foreperiod effect has been often observed in response-speed studies. Different action control frameworks assume that response and stimulus features are integrated into an event file that is retrieved later if features repeat. Yet the role of foreperiods has so far not been investigated in action control. Thus, we investigated the influence of foreperiod on the integration of action-perception features. Participants worked through a standard distractor-response binding paradigm where two consecutive responses are made towards target letters while distractor letters are present. Responses and/or distractors can repeat or change from first to second display, leading to partial repetition costs when only some features repeat or repetition benefits when all features repeat (the difference constituting distractor-response binding). To investigate the effect of foreperiod, we also introduced an anti-geometric distribution of foreperiods to the time interval before the first response display. We observed that distractor-response binding increased with increasing foreperiod duration, and speculate that this was driven by an increase in motor readiness induced by temporal expectancy.

Basal Ganglia Iron in Patients with Multiple Sclerosis Measured with 7T Quantitative Susceptibility Mapping Correlates with Inhibitory Control

BACKGROUND AND PURPOSE

T2 hypointensity in the basal ganglia of patients with MS has been associated with clinical progression and cognitive decline. Our objectives were the following: 1) to compare signal in T2WI, R2 (ie, 1/T2), and R2* (ie, 1/T2*) relaxation rates and quantitative susceptibility mapping; and 2) to investigate the associations among MR imaging, clinical scores, and cognitive measures of inhibitory control linked to basal ganglia functioning.

MATERIALS AND METHODS

Twenty-nine patients with MS underwent a battery of neuropsychological tests including the Flanker and Stroop tasks. 7T MR imaging included 3D gradient-echo and single-echo multishot spin-echo EPI. Quantitative susceptibility mapping images were calculated by using a Wiener filter deconvolution algorithm. T2WI signal was normalized to CSF. R2 and R2* were calculated by log-linear regression. Average MR imaging metrics for the globus pallidus, putamen, and caudate were computed from manually traced ROIs including the largest central part of each structure.

RESULTS

Marked spatial variation was consistently visualized on quantitative susceptibility mapping and T2/T2*WI within each basal ganglia structure. MR imaging metrics correlated with each other for each basal ganglia structure individually. Notably, caudate and putamen quantitative susceptibility mapping metrics were similar, but the putamen R2 was larger than the caudate R2. This finding suggests that tissue features contribute differently to R2 and quantitative susceptibility mapping. Caudate and anterior putamen quantitative susceptibility mapping correlated with the Flanker but not Stroop measures; R2 did not correlate with inhibitory control measures. Putamen quantitative susceptibility mapping and caudate and putamen R2 correlated with the Expanded Disability Status Scale.

CONCLUSIONS

Our study showed that quantitative susceptibility mapping and R2 may be complementary indicators for basal ganglia tissue changes in MS. Our findings are consistent with the hypothesis that decreased performance of basal ganglia-reliant tasks involving inhibitory control is associated with increased quantitative susceptibility mapping.

Comparison of autopsy, X-ray, and M.R.I. findings following a low speed impact to the shoulder

The objectives of the study was to generate data useful to engineers improving crash test dummies and to physicians in anticipating low speed lateral impact injuries to the shoulder. Constant impact mass, distance and variable speeds were used to generate impact forces. Twelve unembalmed human cadavers were studied within 48 hours of death. Pre-test and Post-test physical, X-Ray, and Magnetic Resonance examinations were completed. X-Ray best identified bone injury, Magnetic Resonance intratendinous and intramuscular pathology and autopsy joint instability. Low speed (3.5-7.0 m/sec) impacts under these testing conditions frequently produce soft tissue and bone injuries. Sternoclavicular and acromioclavicular joint instabilities were found in 83% of the cadavers. The most frequent bone fractures were in the distal clavicle of 42% and labral or rotator cuff tears in 13% of the cadavers.

Temporal bone dissection simulation--an update

We report on our continued development of a virtual simulation for temporal bone dissection that provides stereoscopic display, haptic feedback, and aural simulation into a straightforward, comprehensive learning environment. The multimodal interface provides a seamless simulation for non-deterministic drilling and cutting of bone in the surgical context, as well as an intuitive interface for the intelligent tutor for learning regional anatomy. We present novel methodologies for integrating multimodal and multiresolution data sets, including extension to functional and structural segmentation. We will present our initial efforts to validate this environment. Through continued iterations, it is our hope that the system will provide a valuable tool for training future otologic surgeons as well as an environment for the quantitative evaluation of surgical skill.

T1 measurements in cell cultures: a new tool for characterizing contrast agents at 1.5T

The objective of this work was to assess the feasibility and accuracy of T1 and relaxivity measurements in cell cultures using 1.5T magnetic resonance imaging (MRI) with the long-term goal to develop a tool for evaluation of novel paramagnetic agents in a realistic macromolecular environment. This initial study was carried out using MCF-7 cells treated with independently determined concentrations of Gd-DTPA. Two cell culture systems were evaluated: cell pellets and single layers of cells grown on microporous inserts. High-resolution T1 measurements of cell cultures were acquired with two dimensional Inversion Recovery Fast Spin Echo (2D-IR-FSE), three dimensional Inversion Recovery Fast Spin Echo (3D-IR-FSE), and 3D-SPGR sequences. The T1 and relaxivity accuracy of these sequences was confirmed with aqueous Gd-DTPA samples of known concentration. Relaxivities of 1.71 +/- 0.15 [mM(-1)second(-1)] and 1.55 +/- 0.50 [mM(-1)second(-1)] were measured in the cell pellets and cell monolayers, respectively, and were different from the value of 4.3 [mM(-1)second(-1)] for Gd-DTPA in water. Both cell pellets and monolayers are suitable for initial assessment of novel MR contrast agents.

Texture detection of simulated microcalcification susceptibility effects in magnetic resonance imaging of breasts

The presence, size, structure and clustering characteristics of microcalcifications can indicate breast cancer. The magnetic susceptibility of microcalcifications differs from soft biological tissues, leading to directional blurring effects that can be detected by statistical image processing methods. A study of the ability of statistical texture analysis to detect simulated localized blurring in magnetic resonance imaging (MRI) of dense breast is presented. This method can detect localized blurring with sensitivity of 88.89% to 94.44%, specificity of 99.72% to 100%, positive predictive value of 73.91% to 100% and negative predictive value of 99.91% to 99.95%. J. Magn. Reson. Imaging 2001;13:876-881.

Comparison of three-dimensional fast spin echo and gradient echo sequences for high-resolution temporal bone imaging

T2-weighted high-resolution gradient and fast spin echo sequences are widely used as an alternative or adjunct to contrast-enhanced T1-weighted temporal bone imaging. However, to date no systematic comparison has been presented. The purpose of this work is to identify optimal acquisition parameters and to compare volume gradient and fast spin echo techniques. Signal intensities and scan efficiency were computed for gradient echo segment-interleaved motion-compensated acquisition into steady state (SIMCAST), standard fast spin echo (FSE), and fast recovery fast spin echo (FR-FSE). Computations were compared with inner ear images acquired with cubic voxel sizes of 0.35-0.40 mm(3)in 5-8 minutes. Given otherwise identical conditions, the FR-FSE sequence produces images with improved SNR in shorter scan times than standard FSE. For FR-FSE, the scan efficiency is optimal for specific pairs of TR and echo train length, eg, 400 ms/8, 735 ms/16, and 2,050 ms/48. FR-FSE images with large TR and echo trains, while achieving better SNR, are severely compromised by blurring. Imaging with echo train lengths of 16-24 and TR of 800-1,200 ms is a good compromise, and FR-FSE signal-to-noise ratio (SNR) and scan efficiency become comparable to SIMCAST. In vivo image quality is excellent with both FR-FSE and SIMCAST, but SIMCAST images have slightly higher SNR and are significantly more crisp. J. Magn. Reson. Imaging 2000;12:814-825.

Tumor growth and audiometric change in vestibular schwannomas managed conservatively

OBJECTIVE

To prospectively define the correlation between changes in tumor volume and audiometric function in vestibular schwannomas managed conservatively.

STUDY DESIGN

Prospective longitudinal study.

METHODS

Twenty-one patients (age range, 15-84 y; mean age, 63.3 y) with newly diagnosed vestibular schwannomas were enrolled between 1994 and 1999 in a protocol at The Ohio State University Hospital (Columbus, OH) to evaluate the correlation between tumor volume and audiometric change during a period of observation. Patients were evaluated yearly by clinical examination, a standardized internal auditory canal magnetic resonance imaging scan with gadolinium contrast for volumetric analysis, and audiometric function testing. Demographic data, historical features, neurofibromatosis type 2 (NF2) status, initial testing results, and serial testing results were recorded.

RESULTS

An increase in tumor volume occurred in 14 of the 21 patients (66%). The pattern of volumetric change was found to be extremely variable. Multiple regression analysis revealed significant correlations of changes in tumor volume with changes in pure-tone average and speech discrimination score (P < .0001 and P = .0021, respectively). Change in tumor volume had greater effect on pure-tone average and speech discrimination score in patients initially with class D audiometric function when compared with those initially in class A (P = .0083 and P = .0245, respectively). The presence of NF2 had an independent protective effect against deterioration of the pure-tone average when compared with patients without NF2 (P = .0125).

CONCLUSIONS

This study demonstrated a significant correlation between a change in volume and auditory deterioration in vestibular schwannomas being managed with a trial of observation. A given change in tumor volume appeared to have a greater effect on pure-tone average and speech discrimination score as initial auditory classification declined.

Interactive medical data on demand: a high-performance imaged-based approach across heterogeneous environments

Medical data in image format continues to increase in both size and complexity. We have integrated advanced techniques in visualization, networked computing, and interface design to improve methods for accessing medical data comprising high-resolution images for reconstructions into three-dimensional volumetric representations. We present two approaches to handle the range of low to high-end client platforms, support visualization functionality, and provide the ability to manipulate very large data over heterogeneous computing and networking environments. We present examples of its use for clinical, research, and educational purposes and discuss future extensions.

Virtual temporal bone dissection simulation

We have developed a working prototype system for the virtual simulation of temporal bone dissection. The system offers a paradigm from traditional practices by integrating technological advances to provide a safer and more cost effective way to learn fundamental techniques used in temporal bone surgeries. We present our methods to provide a real-time interactive volumetric system that obviates the need for physical materials in initial training, and provides a more accessible way for residents to practice and to increase exposure to pathological variance. Finally, we discuss ways to extend this work to more advanced resident training, presurgical planning, and surgical documentation.

Assessment of internal auditory canal tumors: a comparison of contrast-enhanced T1-weighted and steady-state T2-weighted gradient-echo MR imaging

BACKGROUND AND PURPOSE

Although contrast-enhanced T1-weighted MR imaging is the standard of reference for diagnosing tumor in the cerebellopontine angle, high-resolution T2-weighted imaging may show more details of the seventh and eighth cranial nerve branches, resulting in more accurate tumor volume measurements. The purpose of this study was to compare two MR sequences for their ability to delineate internal auditory canal tumors.

METHODS

Twenty-seven ears in 21 patients with 16 confirmed schwannomas were studied with the 3D T2-weighted prototype segment-interleaved motion-compensated acquisition in steady state (SIMCAST) and the T1-weighted contrast-enhanced spoiled gradient-echo (SPGR) techniques. Twenty-eight axial sections were acquired using parameters of 17/3.3 (TR/TE), a 40 degrees flip angle, a 20 x 15-cm or 22 x 16-cm field of view (FOV), a 512 x 256 matrix, and a 0.4- or 1.2-mm section thickness for the SIMCAST technique, and 30/4.2, a 30 degrees flip angle, a 20 x 20-cm FOV, a 512 x 288 matrix, and a 1.5-mm section thickness for the SPGR technique. Tumor appearance and depiction of surrounding anatomy, including the cranial nerves, were evaluated. Tumor volumes were measured by manual tracing.

RESULTS

Both sequences clearly identified tumors that ranged in size from 0.06 to 3.0 cm3. Measurements on both sequences agreed, on average, within 14%. The information from both sequences was complementary. SIMCAST usually delineated the CSF spaces better, whereas SPGR more clearly showed the tumor/brain boundary.

CONCLUSION

SIMCAST and SPGR are suitable for tumor detection and volume measurements. SPGR has somewhat better contrast, but SIMCAST excels at depicting the surrounding anatomy and tumor involvement of the seventh and eighth cranial nerves.

Paramagnetic oligonucleotides: contrast agents for magnetic resonance imaging with proton relaxation enhancement effects

An antisense paramagnetic oligonucleotide analogue targeted to a model macromolecular receptor (5S rRNA) was prepared. The paramagnetic agent's relaxivity (dependence of the relaxation rate on paramagnetic agent concentration) in the presence and absence of the macromolecular receptor was measured at 1.5 and 6.3 T. The relaxivity of the targeted agent increased specifically in the presence of the macromolecular receptor (16% at 6.3 T and 15% at 1.5 T). This effect was specific for a paramagnetic oligonucleotide targeted to the receptor and was larger than the relaxivity enhancement due simply to receptor-induced viscosity differences. Maximizing this relaxivity enhancement of tumor targeted paramagnetic oligonucleotides will aid in contrast agent development for magnetic resonance imaging.

Endolymphatic sac occlusion for the enlarged vestibular aqueduct syndrome

OBJECTIVE

To test the efficacy of occlusion of the enlarged vestibular aqueduct to treat the progressive sensorineural hearing loss associated with the enlarged vestibular aqueduct (EVA) syndrome.

STUDY DESIGN

Prospective controlled study.

SETTING

Tertiary care referral center.

PATIENTS

Sixteen consecutive patients (29 affected ears) with progressive sensorineural hearing loss and vestibular aqueducts >1.5 mm in diameter without other inner ear anomalies participated in this study.

INTERVENTION

In 10 patients with progressive hearing loss, the EVA was occluded in the ear with worse hearing by placing a fascia graft between the posterior fossa dura overlying the endolymphatic sac and intraosseous duct and the posterior semicircular canal without opening the endolymphatic sac. In the operative ears, serial postoperative audiograms were compared with the contralateral ear in patients with bilateral EVA and with the other nonoperated control ears.

MAIN OUTCOME MEASURES

The rate of decline of pure-tone average and speech discrimination before surgery in the operated ear was compared with the rate of decline postoperatively in the same ear. The rates of decline in the nonoperated contralateral ear from the same patient and the nonoperated control ears from other patients were also used for comparison with the postoperative rate of decline in the operated ears.

RESULTS

There was no statistically significant change in the rate of hearing loss in patients undergoing occlusion of the EVA.

CONCLUSIONS

Extraluminal soft-tissue occlusion of the EVA appears to be a safe procedure but has not yet been shown to be significantly effective in altering the sensorineural hearing loss accompanying the EVA syndrome. Further surgical intervention does not appear warranted until such time that longitudinal follow-up shows sufficient evidence of efficacy of the procedure.

High-resolution MR imaging of the auditory pathway

MR imaging is a valuable tool in the evaluation of the auditory pathway. The current techniques in high-resolution MR imaging of the temporal bone are presented followed by a review of normal anatomy. Several diseases involving the middle ear, inner ear, internal auditory canal, and cerebellopontine angle are then presented. A radiologic-pathologic approach is used to illustrate the nature of these diseases and their appearance on MR imaging.

Development of the force-feedback model for an epidural needle insertion simulator

The Ohio Supercomputer Center and the Department of Anesthesiology at the OSU Medical Center have developed a computer-based simulation system for use in training anesthesiology residents in the technique of placing a needle for an epidural block. Although the simulator has been well regarded, the fidelity of the haptic feedback is limited because it is based on subjective expert-user evaluation and not on objective model-based or data-based empirical methods. Only a single degree of freedom for force-feedback is required. However, the simulation must be able to accurately portray the force required to puncture each layer of tissue in order to feel realistic. The purpose of the research described in this paper was to devise a methodology for creating empirically based realistic force-feedback models for the epidural needle insertion procedure using MRI data and biomechanical data from materials testing.

A segment-interleaved motion-compensated acquisition in the steady state (SIMCAST) technique for high resolution imaging of the inner ear

MRI, with ever-increasing spatial resolution, recently has depicted progressively more anatomic details of the inner ear and is playing an important role in the diagnostic evaluation of patients with sensorineural hearing loss. We present a three-dimensional (3D) segment-interleaved, motion-compensated acquisition in steady state (SIMCAST) sequence that allows further increase in spatial resolution in reasonable scan times minimizing artifacts due to susceptibility and motion. The sequence uses gradient moment nulling over TR and segmented interleaved acquisition of multiple data sets with different radiofrequency (RF) phase-cycling schemes. Combination of data from multiple acquisitions by averaging and maximum intensity projection were compared. Images of phantoms and in vivo inner ears were obtained with both full and fractional echoes and compared with other high resolution techniques such as three-dimensional gradient-echo and two-dimensional (2D) and three-dimensional fast spin-echo (FSE) sequences. The new sequence achieves improved signal-to-noise ratio (SNR) and spatial resolution resulting in improved depiction of inner ear structures.

Introduction of fast MR imaging in the assessment of hepatic steatosis

We determined the utility of fast gradient echo techniques (modified Dixon method) in the assessment of hepatic fat content. Fast spoiled gradient echo was performed on bovine liver/corn oil homogenates with known fat fractions (FFE) to assess the accuracy of fat quantitation (FFMRI). The pulse sequence was manipulated via alterations in TE (echo time), TR (repetition time), and alpha (flip angle). In vivo studies were then performed using breath-holding maneuvers on normal adult volunteers and subjects at risk to develop hepatic steatosis, with cystic fibrosis or morbid obesity. At out-of-phase, TE, TR, and alpha were 2.1 ms, 7.3 ms, and 30-50 degrees and in-phase TE, TR, and alpha were 4.2 ms, 9.3 ms, and 30-50 degrees; FFMRI correlated well with FFE. An elevated fat fraction was observed in a high percentage of subjects with cystic fibrosis and morbid obesity. Fast gradient echo techniques were used successfully in the assessment of hepatic steatosis. The reduced acquisition times permitted in vivo analysis on adults and children using breath hold maneuvers.

High-resolution MR of the intraparotid facial nerve and parotid duct

PURPOSE

To describe a high-resolution MR imaging technique that depicts the complex anatomy of the region of the parotid gland, focusing on the intraparotid components of the facial nerve and parotid duct.

METHODS

High-resolution T1-weighted images of the parotid gland were acquired with a prototype three-dimensional Fourier transform gradient-echo sequence that permits a very short echo time (4.2 milliseconds) by using a modified phase-encoded time-reduced acquisition scheme. The sequences were obtained at 1.5 T with a head and neck coil. Postprocessed multiplanar, curved and volumetric images were obtained. The most clinically useful images were acquired at parameters of 40/4.2 (TR/TEeff) a flip of 30 degrees, a field of view of 18 to 20 cm, a matrix of 512 x 288 or 512 x 256, an axial plane, 60 images, no gaps, and a section thickness of 1.5 mm. Eighteen healthy subjects were examined. The position of the facial nerve within the parotid gland was determined by identifying the facial nerve in the stylomastoid foramen and then following it on sequential sections through the parotid gland. Curved reformations were used to confirm the visibility of the nerve. A similar technique was used for the parotid duct.

RESULTS

The image contrast obtained was similar to that of standard spin-echo T1-weighted images. The parotid gland showed intermediate signal intensity while the fat spaces showed high signal intensity. The vessels had variable signal intensity depending on saturation. The cerebrospinal fluid, nerves, muscles, and ducts had lower signal intensity. In all 18 subjects, the facial nerve from the brain stem to the parotid gland, and the parotid duct from the mouth to the hilus of the gland were seen bilaterally. The proximal intraparotid facial nerve to the level of the retromandibular vein was seen in 72% of the subjects and the main intraparotid ducts were seen in 66% of the subjects.

CONCLUSION

High-resolution MR imaging offers simultaneous display of most of the important structures in the region of the parotid gland, including the intraparotid duct and facial nerve.

Visualization of compression neuropathies through volume deformation

This paper describes an interdisciplinary effort to simulate and visualize the mechanisms involved in compression neuropathies, specifically tissue deformation occurring during vaginal delivery. These neuropathies often evolve into chronic pelvic pain. We present our methodologies of using high resolution magnetic resonance acquisitions from submillimeter pulse sequences to develop interactive computer simulations based on physically plausible volume models to drive 3D simulations of childbirth. This effort will elucidate tissue movements and mechanics involved in pain disorders and better explain the etiology of these disorders.

A volumetric approach to virtual simulation of functional endoscopic sinus surgery

Advanced display technologies have made the virtual exploration of relatively complex models feasible in many applications. Unfortunately, only a few human interfaces allow natural interaction with the environment. Moreover, in surgical applications, such realistic interaction requires real-time rendering of volumetric data-placing an overwhelming performance burden on the system. We report on a collaboration of an interdisciplinary group developing a virtual reality system that provides intuitive interaction with volume data by employing real-time volume rendering and force feedback (haptic) sensations. We describe our rendering methods and the haptic devices and explain its utility of this system in the real-world application of Endoscopic Sinus Surgery (ESS) simulation.

Submillimeter magnetic resonance imaging of the temporal bone in Meniere's disease

The pathoetiology of Meniere's disease remains elusive. Histopathologic and imaging studies have implicated congenital or developmental abnormality of the endolymphatic duct as a likely predisposing factor to the development of endolymphatic hydrops and clinical Meniere's disease. Recently, improved high-resolution magnetic resonance imaging (MRI) protocols have allowed better demonstration of the soft tissues of the endolymphatic duct and sac. This study is a prospective evaluation of the ability of submillimeter MRI to detect the endolymphatic duct in Meniere's disease patients and control subjects. In addition, the development of the temporal bone in the region of the endolymphatic sac and duct is evaluated by measurements of the distance from the posterior semicircular canal to the subarachnoid space and the distance from the vestibule to the subarachnoid space. Visualization of the endolymphatic duct was found to be significantly less frequent in the Meniere's disease patients (29%) than in the control subjects (91%). Temporal bone measurements in the region of the endolymphatic duct showed patients with Meniere's disease to have smaller dimensions than control subjects.

Submillimeter-resolution MR of the endolymphatic sac in healthy subjects and patients with Menière disease

PURPOSE

To evaluate the utility of submillimeter resolution MR imaging for direct depiction of functional soft-tissue components of the intraosseous endolymphatic duct and sac in healthy subjects and in patients with Menière disease.

METHODS

Axial MR images were acquired of 14 patients with Menière disease and 14 healthy volunteers at 1.5 T with a short-echo-time steady-state 3-D gradient-echo sequence. Seven volunteers and eight patients were also studied with a T1-weighted 3-D spoiled gradient-echo sequence. T1/T2 relaxation times were estimated from studies with multiple flip angles.

RESULTS

Independent of the acquisition method, intraosseous endolymphatic ducts and sacs were seen unambiguously in the ears of 20 of 21 healthy subjects but in only four of 12 asymptomatic and two of 10 symptomatic ears of patients with Menière disease. Other labyrinthine structures were well depicted in all subjects. Furthermore, shorter relaxation times were measured for the contents of the vestibular aqueduct than for other labyrinthine structures.

CONCLUSION

In our high-resolution study, the intraosseous portions of the endolymphatic ducts and sacs were depicted in most of the healthy subjects. They were frequently not seen in either ear of patients with unilateral Menière disease, presumably because of their small size.

Adaptive filtering for high resolution magnetic resonance images

We present a study of least mean square (LMS) based adaptive filters for high resolution magnetic resonance (MR) images to improve signal-to-noise ratio (SNR) while maintaining sharp edges. Five variations of a new technique that senses the type of noise or the presence of an edge in the filtering window, called adaptive filtering with noise estimation (AFEN) are presented and compared with the basic two-dimensional LMS (TDLMS) algorithm, adaptive filtering with a mean estimator (AFLME), a two-dimensional averaged LMS (TDALMS) algorithm, and a two-dimensional median weighted LMS (TDMLMS) algorithm. Although TDLMS, TDALMS, and TDMLMS filters give better SNR improvement when applied uniformly to an image, they significantly blur edges. The AFLME and AFEN filters both show approximately a factor of 2 SNR improvement with much better retention of edges, with AFEN showing slightly better performance for both SNR and edge sharpness in phantom and in vivo inner ear images.

Cranial base tumor visualization through high-performance computing

Tumors of the skull base in general are considered among the more difficult head and neck pathological entities to treat surgically; some surgeons, in fact, consider lesions in this area inoperable. The most appropriate and safest surgical approach to lesions of the anterior and lateral skull base can be devised only with accurate and precise pre-operative assessment. The literature demonstrates the constant evolution of and search for more efficient less invasive, and safe surgical approaches to this region. With the development of a more exact three-dimensional, interactive anatomical "road map" for each patient's disease and anatomy, the skull base surgeon can not only achieve a more accurate pre-operative assessment leading to a less invasive and less morbid approach, but also can continue to develop and refine new approaches without fear of actual morbidity and mortality. An interdisciplinary team approach, the advent and continued development of faster high performance computers, and the development of new and innovative rendering algorithms can lead to surgical simulation. A prototype of an interactive system has been developed. The system will be iteratively modified through a stepwise evaluation of its clinical usefulness by continually reassessing the system with clinical trials. The current state of the system and the potential benefits are presented.

Reformatted planar 'Christmas tree' MR appearance of the endolymphatic sac

A high-resolution three-dimensional Fourier transform technique and prototype bilateral dual phased-array surface coil technique was used to make inner ear structures visible on MR. Multiplanar reformatted images, parallel to the plane of the vestibular aqueduct, allowed viewing of the entire endolymphatic sac/vestibular aqueduct on one section, producing a "Christmas tree" shape. The reformation was obtained using a double oblique angle, 45 degrees from true sagittal and 70 degrees from the orbital-meatal axis.

Fabrication of vascular replicas from magnetic resonance images

Image processing and Computer Numerical Controlled (CNC) machining techniques have been used to prepare a large-than-life investment cast of an aortic bifurcation from magnetic resonance images of a replica of the vessel. The technique will facilitate experimental studies of vascular fluid dynamics and permit the in vitro reproduction of flows in living subjects.

Magnetic susceptibility artifacts on high-resolution MR of the temporal bone

PURPOSE

To determine whether signal variations and subtle anatomic deformities observed in high-resolution MR studies of temporal bones were caused by the large susceptibility differences at air-fluid interfaces near the round and oval window.

METHODS

A systematic study of healthy subjects and plastic phantoms was conducted. The phantom consisted of a series of cylindrical holes of various small sizes within a solid block of plastic. These holes were partially filled with water and then covered with a reservoir of gelatin to simulate the otic capsule air-water interfaces. On a 1.5-T system, T2-weighted fast spin-echo images and three-dimensional Fourier transform gradient acquisition in steady state images were obtained using dedicated phased-array radio frequency coils. The directions of the frequency and in-plane phase-encoding gradients were swapped, and the receiver bandwidth was changed to demonstrate the dependence of the artifacts on these parameters.

RESULTS

The phantom images confirmed and characterized artifacts consistent with magnetic susceptibility differences at the air-water interfaces. There is a combination of signal loss, misregistration in the frequency-encoding direction, and high signal foci related to the air-water interfaces. Furthermore, the artifacts were worse with narrower receiver bandwidth. Similar consistent artifact patterns were seen near the oval and round windows in studies of healthy subjects.

CONCLUSIONS

In high-resolution MR imaging there are significant deformities in the display of the normal anatomy because of magnetic susceptibility.

Phased array coils for upper extremity MRA

A phased array coil was constructed for imaging the upper extremity vasculature for patients undergoing dialysis treatment. The phased array coil exhibits improved signal-to-noise ratio (SNR) over the body coil and allows imaging of the entire upper extremity. SNR as a function of depth was measured on a homogeneous phantom with the arm coil and compared with the body coil. Near the coil there is an improvement of a factor of 7 and at a depth of approximately 6-7 cm, there is an improvement of factor 2. In vivo SNR measurements resulted in similar improvements. Images of the upper extremity vasculature of healthy volunteers were generated using 2D-time-of-flight (2DTOF) angiography. Blood flow velocity was assessed in a CINE-phase contrast study.

Phased array RF coils for high-resolution MRI of the inner ear and brain stem

OBJECTIVE

The spatial resolution in MRI is predominantly limited by the available signal-to-noise ratio (S/N). To increase the S/N, a four coil phased array consisting of bilateral pairs of semioval coils was constructed for high resolution imaging of the temporal bone and brainstem.

MATERIALS AND METHODS

Coil sizes of 10 x 6 and 6 x 4.5 cm were tested. The S/N values were measured in vivo and with homogeneous phantoms and compared to commercial 3 in receive and quadrature head coils.

RESULTS

At a depth of 4-5 cm, phantom studies yielded S/N improvements of a factor of 1.26-1.37 with the large array compared to the 3 in coil and 2.33-1.74 compared to the head coil. Similar improvements (1.16 and 2.37) were obtained in inner ear images. No further improvement was achieved at this depth with the small array. At a depth of 8 cm, phantom studies yielded similar S/N for the quadrature head coil and two bilaterally placed large array coils, while a factor of 1.27 was obtained in brainstem images.

CONCLUSION

The use of phased array coils yields significantly increased S/N and is thus valuable for high resolution MRI.

Echo-time reduction for submillimeter resolution imaging with a 3D phase encode time reduced acquisition method

To achieve optimal image quality and highest spatial resolution for inner ear imaging with a 3D gradient echo sequence, it is necessary to minimize susceptibility dephasing effects by using very short TE. Fractional RF pulses and echoes can yield short TE for moderate spatial resolution; however, for voxel size of less than 1 mm, TE is limited by the phase encode gradients. We present a method to obtain very short effective TE by using short triangular shaped phase encode gradients to sample the central portions of k-space and progressively longer trapezoidal gradients for the outer portions of k-space. A 3D pulse sequence employing the modified phase encoding scheme for both in-plane and slice phase encoding directions was implemented and tested on phantoms and in vivo. The effective TE equals the minimal TE used for the central k-space portions. Submillimeter resolution (0.35 x 0.35 x 0.7 mm3) images of the inner ear were obtained with effective TE of 3.2 ms and were compared with standard 3D images with TE of 8 ms. With this pronounced TE reduction, the susceptibility artifacts at air/fluid interfaces are significantly reduced.

Proton magnetic resonance spectroscopy (1H MRS) of the hippocampal formation in schizophrenia: a pilot study

BACKGROUND

Recent post-mortem and magnetic resonance imaging (MRI) studies strongly suggest a decrease in the volume of the hippocampus and other limbic temporal structures in schizophrenia. Therefore, we hypothesised that N-acetyl aspartate (NAA) which is found mainly in neurons and which can be measured by proton magnetic resonance spectroscopy (1H MRS) would be decreased in the limbic temporal region in schizophrenia.

METHOD

Consenting subjects fulfilling DSM-III-R criteria for schizophrenia (n = 11) and matched healthy volunteers (n = 11) who were recruited in a tertiary university referral centre, participated in a 1H MRS brain study. Proton MRS spectra were obtained from a 12 cm3 voxel (2 x 2 x 3 cm) in the right and left hippocampus/amygdala region. A researcher blind to the source of the spectra, measured the NAA intensity in all subjects, which were then statistically compared across the two groups.

RESULTS

NAA intensities were significantly reduced in the right hippocampus/amygdala region of schizophrenic patients (P = 0.038). The difference of the left side did not reach significance at the 95% confidence level.

CONCLUSIONS

The findings of decreased NAA in this study suggest that there may be a decrement in neuronal number or tissue volume of the right hippocampal/amygdala region in schizophrenia. Biochemical alterations in the metabolism of NAA in schizophrenia may be an alternative explanation. The findings are consistent with other types of post-mortem and in vivo evidence for hypoplasia of the limbic temporal structures in schizophrenia, postulated to be of neurodevelopmental pathogenesis.

Measurement of the geometric parameters of the aortic bifurcation from magnetic resonance images

This paper presents a method for measuring arterial geometry in vivo using MRI. The approach was validated using MR images of three perfused compliant casts of human aortic bifurcations whose geometry was known. Preliminary human studies demonstrated the reproducibility of the technique. The approach was applied to 20 normal individuals to study the effects of age, race, and gender on the geometry of the aortic bifurcation. The results show that older people tend to have a smaller bifurcation angle, lower planarity, and larger angular asymmetry than younger people. Asians have larger bifurcation angles than whites. The bifurcation of males is more asymmetric than that of females. These results may have implications regarding the heritability of arterial geometry, the similarities of cardiovascular risk within families, and differences in risk among groups.

Water and fat MR imaging with chemical shift selective 3D steady state methods

A new 3D acquisition regimen that enables the collection of conventional, water-suppressed, and fat-suppressed images with no increase in scan times compared with currently implemented 3D sequences is presented. The method is based on conventional 3D steady state with interleaved selective excitation of the fat resonance resulting in acquisition of a fat-based image during the TR period experienced by the water spins. This new sequence is relatively tolerant to susceptibility artifacts and results in excellent water-based images. Because the idea, which we propose, is independent of the type of steady-state imaging protocol utilized, it can be easily applied with regimens that are specifically tailored to enhance contrast.

Three-dimensional steady-state MR angiography of the lower extremities

Volume steady-state black-blood magnetic resonance imaging was evaluated as a method for depicting lower extremity vasculature. In steady-state imaging, flow has low signal intensity because motion destroys the coherence of transverse magnetization. To optimize image contrast, computations and measurements were obtained for the three-dimensional (3D) GRASS (gradient-recalled acquisition in the steady state) and 3D SSFP (steady-state free precession) sequences and a range of TRs and flip angles to determine optimal vessel-muscle contrast. The best results were achieved with a 3D GRASS sequence with a TR msec/TE msec of 25/5 and a flip angle of 30 degrees. Coronal images of the femoral and popliteal vessels were obtained in healthy volunteers with various fields of view and voxel sizes. Inflow of unsaturated spins from outside the image region, yielding high signal intensity, could be a potential drawback in steady-state black-blood imaging; however, problems can be avoided by using coronal acquisitions and large fields of view. Steady-state black-blood imaging depicts vessels with high accuracy and is faster and free of flow artifacts.

Magnetic resonance angiography in the preoperative evaluation of abdominal aortic aneurysms

Magnetic resonance angiography (MRA) and magnetic resonance imaging (MRI) are noninvasive techniques of visualizing blood vessels without the use of intravenous contrast or ionizing radiation. This prospective study assessed preoperative MRA and MRI in the evaluation of 28 patients with abdominal aortic aneurysm (AAA). MRI and MRA accurately predicted the extent of cephalad AAA, the patency of the superior mesenteric artery, and the course of the left renal vein, but were less accurate in defining the extent of caudal AAA, flow of the inferior mesenteric artery, and multiple renal arteries. This study suggests that MRI and MRA are alternatives to the combination of angiography and computed tomographic scan in the preoperative evaluation of patients with suspected AAA and no evidence of mesenteric or renal ischemia. When combined with preoperative segmental Doppler arterial studies, an accurate surgical plan may be formulated. Further refinements in image acquisition and postprocessing software analysis will advance the use of MRI and MRA for complete evaluation prior to elective AAA repair.

Optimization of submillimeter-resolution MR imaging methods for the inner ear

Submillimeter-resolution magnetic resonance (MR) imaging of the inner ear is valuable for diagnosis and treatment planning. Its main advantage for investigations of underlying disease is that it can directly depict the fluid spaces of the membranous labyrinth rather than define only the bony canal, as does computed tomography. A systematic evaluation of factors influencing high-resolution three-dimensional (3D) gradient-echo imaging of the inner ear with a standard clinical MR system is presented. This includes the evaluation of various radio-frequency coils, the design of steady-state pulse sequences, and the optimization of acquisition parameters. A quantitative analysis was facilitated by computer simulations and image processing. The highest signal-to-noise ratio for the membranous labyrinth was obtained with a single 3-inch (7.6-cm) receiver coil and a 3D GRASS (gradient-recalled acquisition in the steady state) sequence with the minimal achievable TR msec/TE msec of 25/7 and a 40 degrees--60 degrees flip angle, which yielded acceptable images with minimal voxel volumes of 0.1 mm3 in 14 minutes.