Can we trust elderly donor grafts for corneal transplantation?
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Age Factors↗
Biomedical subjects
C H Meyer
Publications and source records attributed to C H Meyer.
Efficient off-resonance correction for spiral imaging.
A new spiral imaging technique incorporates the acquisition of a field map into imaging interleaves. Variable density spiral trajectories are designed to oversample the central region of k-space, and interleaves are acquired at two different echo times. A field map is extracted from this data and multifrequency reconstruction is used to form an off-resonance corrected image using the entire dataset. Simulation, phantom, and in vivo results indicate that this technique can be used to achieve higher image and/or field map spatial resolution compared to conventional techniques. Magn Reson Med 45:521-524, 2001.
Artifacts↗
Real-time interactive coronary MRA.
An interactive real-time imaging system capable of rapid coronary artery imaging is described. High-resolution spiral and circular echo planar trajectories were used to achieve 0.8 x 1.6 mm2 resolution in 135 ms (CEPI) or 1.13 x 1.13 mm2 resolution in 189 ms (spirals), over a 20-cm FOV. Using a sliding window reconstruction, display rates of up to 37 images/sec were achieved. Initial results indicate this technique can perform as a high-quality 2D coronary localizer and with SNR improvement may enable rapid screening of the coronary tree.
CD-I↗
Retinal pigment epithelial tear with vitreomacular attachment: a novel pathogenic feature.
BACKGROUND: The development of tears of the retinal pigment epithelium (RPE) has classically been described with or without choroidal neovascularization (CNV) or after laser treatment. Tangential shear forces within the RPE or CNV are usually considered to cause the dehiscence. METHODS: Three patients with CNV and spontaneous RPE tear and additional vitreomacular traction were examined by fluorescein angiography (FA), optical coherence tomography (OCT) and kinetic ultrasound. RESULTS: From the pre-tear to the tear stage a sudden decrease in vision was observed. Fluorescein angiographic images demonstrated RPE-tear formation with blocked filling in the area of the contracted RPE and a well-demarcated hyperfluorescence in the bed of the torn RPE. OCT-scans demonstrated vitreomacular traction at the foveal area in all three cases. Kinetic ultrasound revealed vitreous attachments at the optic disc and fovea. CONCLUSION: Magnitude, variation of mechanical forces, and the continuous shear stress of the aged vitreous gel transmitted across vitreoretinal attachments may cause a chronic stimulus to retina and RPE. Vitreomacular traction may contribute to the subsequent formation of RPE tears via mechanical or cell mediator pathways.
Aged↗
Macular translocation with radial scleral ouffolding: experimental studies and initial human results.
PURPOSE: Different techniques have been proposed for translocating the macula in patients with subfoveal neovascularization secondary to age-related macular degeneration. A new approach utilizing radial outfolding of the sclera was investigated. MATERIALS AND METHODS: Surgical techniques and retinal displacement were evaluated in animal trials using metal scleral clips. Successful translocation and reattachment of the retina was achieved in eight rabbits (eight eyes). We conducted a retrospective review of macular translocation surgery, performed with radial scleral outfolding, in a series of five consecutive human patients (five eyes) using full-thickness transscleral mattress sutures. RESULTS: After surgery, vision improved in two of five patients, with one patient achieving a visual acuity of 20/50. The mean angle of rotation was 11.5 deg (range 8.6 -15.1). The mean amount of foveal displacement was 1,276 pm (range 852-1,620). Complications included one case of retinal detachment, one of diplopia, and one of subretinal hemorrhage. CONCLUSIONS: Limited macular translocation by radial scleral outfolding can improve vision in selected patients. Radial evagination appears to be as effective as circumferential infolding.
Aged↗
Induced corneal astigmatism after macular translocation surgery with scleral infolding.
OBJECTIVE: To document the corneal astigmatism that occurs with macular translocation after scleral infolding surgery. DESIGN: Retrospective case series of a nonrandomized clinical trial. PARTICIPANTS: Eight consecutive age-related macular degeneration patients (eight eyes) with choroidal neovascularization who underwent macular translocation with scleral infolding at the Duke University Eye Center from December 1998 through October 1999. METHODS: We retrospectively reviewed the charts of eight consecutive patients who underwent macular translocation surgery involving scleral infolding in the superotemporal quadrant. Two patients subsequently underwent release of scleral infolding. MAIN OUTCOME MEASURES: After surgery, these eyes were evaluated for corneal astigmatism with manifest refraction, keratometry, and computerized corneal topography. RESULTS: All eight eyes of eight patients revealed marked degrees of corneal astigmatism. Measurement of astigmatism via manifest refraction, keratometry, and corneal topography confirmed postoperative astigmatism corresponding to the axis of the scleral infolding. The amount of corneal astigmatism ranged from 1.75 to 7.37 diopters (D; mean, 4.60 D), with steepening along the axis of scleral infolding in the superotemporal quadrant of each eye (mean, 42.50 degrees from vertical; range, 24 degrees -66 degrees from vertical). Release of scleral infolding in two patients resulted in significant reduction of corneal astigmatism. CONCLUSIONS: Scleral shortening procedures used in macular translocation surgery may induce large amounts of corneal astigmatism. These patients should be assessed with keratometry and corneal topography to determine the accurate amount and axis. Thereafter, contact lens fitting or scleral infolding release may be considered as therapeutic options for large amounts of astigmatism persisting after surgery.
Astigmatism↗
Rapid evaluation of left ventricular volume and mass without breath-holding using real-time interactive cardiac magnetic resonance imaging system.
OBJECTIVES: The purpose of this study was to validate cardiac measurements derived from real-time cardiac magnetic resonance imaging (MRI) as compared with well-validated conventional cine MRI. BACKGROUND: Although cardiac MRI provides accurate assessment of left ventricular (LV) volume and mass, most techniques have been relatively slow and required electrocardiogram (ECG) gating over many heart beats. A newly developed real-time MRI system allows continuous real-time dynamic acquisition and display without cardiac gating or breath-holding. METHODS: Fourteen healthy volunteers and nine patients with heart failure underwent real-time and cine MRI in the standard short-axis orientation with a 1.5T MRI scanner. Nonbreath-holding cine MRI was performed with ECG gating and respiratory compensation. Left ventricular end-diastolic volume (LVEDV), left ventricular endsystolic volume (LVESV), ejection fraction (EF) and LV mass calculated from the images obtained by real-time MRI were compared to those obtained by cine MRI. RESULTS: The total study time including localization for real-time MRI was significantly shorter than cine MRI (8.6 +/- 2.3 vs. 24.7 +/- 3.5 min, p < 0.001). Both imaging techniques yielded good quality images allowing cardiac measurements. The measurements of LVEDV, LVESV, EF and LV mass obtained with real-time MRI showed close correlation with those obtained with cine MRI (LVEDV: r = 0.985, p < 0.001; LVESV: r = 0.994, p < 0.001; EF: r = 0.975, p < 0.001; LV mass: r = 0.977, p < 0.001). CONCLUSIONS: Real-time MRI provides accurate measurements of LV volume and mass in a time-efficient manner with respect to image acquisition.
Adult↗
Successful macular translocation with temporary scleral infolding using absorbable sture.
PURPOSE: To describe successful macular translocation with temporary scleral infolding in a series of patients with small subfoveal choroidal neovascularization due to age-related macular degeneration or ocular histoplasmosis syndrome. METHODS: Ten eyes of 10 consecutive patients were studied in a prospective, nonrandomized clinical trial. Macular translocation with scleral infolding (MTSI) was performed. Absorbable polyglactin suture was used to create temporary scleral infolding. Distance and stability of retinal translocation, corneal topography, visual acuity, and rates of complications were measured. RESULTS: The median distance of translocation in the early postoperative period was 1,700 microm (range, 680-3,200) and did not regress after resolution of the scleral infolding. Induced postoperative oblique corneal astigmatism resolved, coinciding with the disappearance of peripheral retinal elevation due to scleral infolding. Three patients gained more than two lines of vision, two patients were within two lines of preoperative vision, and five patients lost more than two lines of vision. Complications were similar to previously published reports. CONCLUSION: Temporary scleral infolding is an effective technique in MTSI. The distance of translocation is comparable to that achieved with nonabsorbable suture or scleral resection, and does not regress after resolution of the scleral infolding. Induced postoperative corneal astigmatism appears to resolve.
Aged↗
Combined connectivity and a gray-level morphological filter in magnetic resonance coronary angiography.
A connectivity algorithm combined with a new gray-level morphological filter dramatically improves the segmentation of tortuous coronary arteries from 3D MRI. Small coronary arteries are segmented from the larger ventricles with a new filter. These blood vessels are segmented from the noise background with connectivity. Coronary angiograms were computed in nine datasets acquired on volunteers with 3D stack of spirals and contrast-enhanced navigator sequences by both a maximum intensity projection and surface rendering. Surface images provided depth information needed to distinguish branching arteries from crossing veins. Magn Reson Med 43:892-895, 2000.
Algorithms↗
[Correlation of morphologic changes between optical coherence tomography and topographic angiography in a case of gyrate atrophy].
PURPOSE: To characterize ultrastrructual changes in atrophic disease of the retina, RPE and choroid as seen with gyrate atrophy using two new diagnostic modalities, optical coherence tomography (OCT) and topographic angiography. PATIENT AND METHOD: OCT images were taken in a patient with pericentral choroidal atrophy using a slit-lamp-adapted OCT system. Ophthalmoscopy, conventional and topographic angiographic findings were correlated to the reflectivity changes as seen on OCT. RESULTS: Areas of chorioretinal atrophy correlated with a loss of reflectivity in the RPE-choriocapillaris complex on OCT. Additionally OCT identified a thinning of the nerve fiber layer. Topographic angiography demonstrated an extensive defect, seen as an area of depression, consistent with a loss of choriocapillaris and larger-sized choroidal vessels. In contrast to conventional angiography, central islands were not found to demonstrate structural intensity, while the midperipheral surrounding area was clearly elevated to physiological levels. CONCLUSION: OCT and topographic angiography provide in vivo insight into morphologic changes within neurosensory retina and choroid caused by pericentral choroidal atrophy.
Choroid↗
The real-time interactive 3-D-DVA for robust coronary MRA.
A graphical user interface (GUI) has been developed which enables interactive feedback and control to the real-time diminishing variance algorithm (DVA). This interactivity allows the user to set scan parameters, view scan statistics, and view image updates during the course of the scan. In addition, the DVA has been extended to simultaneously reduce motion artifacts in three dimensions using three orthogonal navigators. Preliminary in vivo studies indicate that these improvements to the standard DVA allow for significantly improved consistency and robustness in eliminating respiratory motion artifacts from MR images, particularly when imaging the coronary arteries.
Algorithms↗
Fast magnetic resonance coronary angiography with a three-dimensional stack of spirals trajectory.
In this work, three-dimensional (3D) spiral imaging has been utilized for magnetic resonance coronary angiography. Spiral-based 3D techniques can dramatically reduce imaging time requirements compared with 3D Fourier Transform imaging. The method developed here utilized a "stack of spirals" trajectory, to traverse 3D k-space rapidly. Both thick-slab volumes encompassing the entire coronary tree with isotropic resolution and thin-slab volumes targeted to a particular vessel of interest were acquired. Respiratory compensation was achieved using the diminishing variance algorithm. T2-prepared contrast was also applied in some cases to improve contrast between vessel and myocardium, while off-resonance blurring was minimized by applying a linear correction to the acquired data. Images from healthy volunteers were displayed using a curved reformatting technique to view long segments of vessel in a single projection. The results demonstrate that this 3D spiral technique is capable of producing high-quality coronary magnetic resonance angiograms.
Algorithms↗
Prospective MR signal-based cardiac triggering.
A cardiac motion compensation method using magnetic resonance signal-based triggering is presented. The method interlaces a triggering pulse sequence with an imaging sequence. The triggering sequence is designed to measure aortic blood velocity, from which cardiac phase can be inferred. The triggering sequence is executed repeatedly and the acquired data processed after each sequence iteration. When the desired phase of the cardiac cycle is detected, data are acquired using the imaging sequence. A signal-processing unit of a conventional scanner is used to process the triggering data in real time and issue triggering commands. Alternatively, a workstation, with a bus adaptor, can access data as they are acquired, process and display the data, and issue triggering commands. With a graphical user interface, the triggering pulse sequence and data-processing techniques can be modified instantaneously to optimize triggering. The technique is demonstrated with coronary artery imaging using both conventional two-dimensional Fourier transform scans and spiral trajectories.
Aorta, Thoracic↗
Reduced spatial side lobes in chemical-shift imaging.
Density-weighted k-space sampling with spiral trajectories is used to reduce spatial side lobes in chemical-shift imaging (CSI). In this method, more time is spent collecting data at the center of k space and less time at the edges of k space in order to make the sampling density proportional to a given apodization function, subject to constraints imposed by gradient performance and Nyquist sampling. The efficient k-space coverage of spiral-based trajectories enables good control over the sampling density within practical in vivo scan times. The density-weighted acquisition is compared to a conventional, nonweighted spiral sampling without the application of a window function. For a fixed voxel size and imaging time, the noise variance is observed to be the same for both cases, while spatial side lobes are greatly reduced with the variable-density sampling. This method is demonstrated on a normal volunteer by imaging of brain metabolites at 1.5 T with both single slice CSI and volumetric CSI. Magn Reson Med 42:314-323, 1999.
Brain↗
3D MR coronary artery segmentation.
Coronary arteries are segmented from the blood pool using mathematical morphology operations from a 3D magnetic resonance spiral acquisition on a continuously breathing healthy volunteer. The segmented volume is maximal intensity projected at different views to yield coronary angiograms showing the left anterior descending artery (LAD), right coronary artery (RCA), and left circumflex artery (LCX). Magnetic resonance coronary angiography provides a retrospective rotating view of the coronary artery tree that complements oblique reformatted sections.
Algorithms↗
New real-time interactive cardiac magnetic resonance imaging system complements echocardiography.
OBJECTIVES: We conducted an initial clinical trial of a newly developed cardiac magnetic resonance imaging (CMRI) system. We evaluated left ventricular (LV) function in 85 patients to compare the clinical utility of the CMRI system with echocardiography, the current noninvasive gold standard. BACKGROUND: Conventional CMRI systems require cardiac-gating and respiratory compensation to synthesize a single image from data acquired over multiple cardiac cycles. In contrast, the new CMRI system allows continuous real-time dynamic acquisition and display of any scan plane at 16 images/s without the need for cardiac gating or breath-holding. METHODS: A conventional 1.5T Signa MRI Scanner (GE, Milwaukee, Wisconsin) was modified by the addition of an interactive workstation and a bus adapter. The new CMRI system underwent clinical trial by testing its ability to evaluate global and regional LV function. The first group (A) consisted of 31 patients with acceptable echocardiography image quality. The second group (B) consisted of 31 patients with suboptimal echocardiography image quality. The third group (C) consisted of 29 patients with severe lung disease or congenital cardiac malformation who frequently have suboptimal echo study. Two independent observers scored wall motion and image quality using the standard 16-segment model and rank-order analysis. RESULTS: CMRI evaluation was complete in less than 15 min. In group A, no significant difference was found between ECHO and CMRI studies (p = NS). In group B, adequate visualization of wall segments was obtained 38% of the time using ECHO and 97% of the time using CMRI (p < 0.0001). When grouped into coronary segments, adequate visualization of at least one segment occurred in 18 of 30 patients (60%) with ECHO and in all 30 patients (100%) with CMRI (p < 0.0001). In group C, adequate visualization of the wall segments was obtained in 58% (CI 0.53-0.62) of the time using echocardiography and 99.7% (CI 0.99-1.0) of the time using CMRI (p < 0.0001). CONCLUSIONS: The new CMRI system provides clinically reliable evaluation of LV function and complements suboptimal echocardiography. In comparison with the conventional CMRI, the new CMRI system significantly reduces scan time, patient discomfort and associated cost.
Adolescent↗
Reducing flow artifacts in echo-planar imaging.
Echo-planar imaging (EPI) is very susceptible to flow artifacts. Two ways to improve its flow properties are presented. First, "partial flyback" is proposed to reduce artifacts arising from flow in the readout direction. Near the center of k-space, only the even echoes of the EPI echo-train are used. Partial flyback is shown to improve the readout-flow properties at the expense of a slight worsening of the phase-encode flow and off-resonance properties. We recommend that the flyback region acquire 95% of the energy in k-space. Second, "inside-out" EPI is used to reduce artifacts arising from flow in the phase-encode direction. Data collection begins at the center of k-space, with separate interleaves to acquire the top and bottom, halves of k-space. Partial flyback is combined with partial-Fourier EPI and inside-out EPI. Partial-flyback inside-out EPI has worse off-resonance properties than partial-flyback partial-Fourier EPI but demonstrates better flow properties and does not require partial k-space reconstruction.
Heart↗
Real-time interactive MRI on a conventional scanner.
A real-time interactive MRI system capable of localizing coronary arteries and imaging arrhythmic hearts in real-time is described. Non-2DFT acquisition strategies such as spiral-interleaf, spiral-ring, and circular echo-planar imaging provide short scan times on a conventional scanner. Real-time gridding reconstruction at 8-20 images/s is achieved by distributing the reconstruction on general-purpose UNIX workstations. An X-windows application provides interactive control. A six-interleaf spiral sequence is used for cardiac imaging and can acquire six images/s. A sliding window reconstruction achieves display rates of 16-20 images/s. This allows cardiac images to be acquired in real-time, with minimal motion and flow artifacts, and without breath holding or cardiac gating. Abdominal images are acquired at over 2.5 images/s with spiral-ring or circular echo-planar sequences. Reconstruction rates are 8-10 images/s. Rapid localization in the abdomen is demonstrated with the spiral-ring acquisition, whereas peristaltic motion in the small bowel is well visualized using the circular echo-planar sequence.
Abdomen↗