Anterior chamber configuration in patients with glaucoma: MR gonioscopy evaluation with half-Fourier single-shot RARE sequence and microscopy coil

Precise size evaluation of extraocular muscles using fat-suppressed fast T1-weighted gradient-recalled echo imaging and multiple gaze fixation targets

PURPOSE

We studied the feasibility of the precise size measurement of extraocular muscles using fast magnetic resonance imaging sequences and gaze fixation targets.

MATERIALS AND METHODS

We recruited 20 healthy volunteers and optimized fat-suppressed fast T1-weighted gradient-recalled echo (FS T1-GRE) and single-shot fast spin-echo (SSFSE) imaging for evaluating extraocular muscles. With each eye at 40° abduction and adduction, we scanned the short-axis plane at the maximum diameter of the bilateral lateral and medial rectus muscles and measured the maximal cross-sectional area of the muscles during extension and contraction. We evaluated interobserver reproducibility and variability between the size measurements using the two MR sequences and the measurement reproducibility using FS T1-GRE imaging.

RESULTS

The interobserver reproducibility in the muscle size measurements using FS T1-GRE and SSFSE imaging was excellent (r = 0.93-0.94) and moderate to good (r = 0.54-0.75), respectively. The interobserver variability was less with FS T1-GRE than SSFSE imaging (p < 0.01). The reproducibility of the size measurement using FS T1-GRE was good to excellent (r = 0.78-0.92).

CONCLUSION

FS T1-GRE imaging with the subject staring at each of multiple targets is useful for evaluating precisely the size of extraocular muscles.

Ocular volumetry using fast high-resolution MRI during visual fixation

BACKGROUND AND PURPOSE

Volumetry may be useful for evaluating treatment response and prognosis of intraocular lesions. Phantom, volunteer, and patient studies were performed to determine whether ocular MR volumetry is reproducible.

MATERIALS AND METHODS

Half-Fourier single-shot RARE and FSPGR sequences at 1.5T with a 76-mm-diameter surface coil were optimized to obtain still ocular images. Volumetry accuracies of each sequence were compared with simulated subretinal phantom volumes. Ocular volumetry was performed in 15 volunteers twice in 1 week by using contiguous axial images of the globes while the subjects stared at a target, and images were acquired in 2 seconds before the subjects were instructed to blink, with this process repeated as necessary. Imaging, intraobserver, and interobserver reproducibility for volumes of the whole eyeball and anterior chamber were assessed. Ocular volumetry was also performed in 6 patients with intraocular tumors before and after treatment.

RESULTS

The phantom study demonstrated that measurement error rates with RARE were significantly lower than with FSPGR (P<.01). The volunteer study demonstrated excellent imaging and intraobserver reproducibility of RARE volumetry for whole eyeballs and anterior chambers (P<.01). Although no interobserver differences were observed in anterior chamber volume measurement (P=.33), there was a significant difference between the 2 observers in eyeball volume measurement (P<.01). Follow-up volumetric data were useful for treatment decisions in all patients.

CONCLUSIONS

Ocular volumetry from contiguous ultrafast RARE images obtained during visual fixation is feasible in volunteer and patient studies and is superior to FSPGR images.

Clinical applications of high-resolution ocular magnetic resonance imaging

Magnetic resonance imaging (MRI) using fast sequences with subjects staring at a target can provide motion-free ocular images, and small receiver surface coils make it possible to produce ocular images with high spatial resolution. MRI using half-Fourier single-shot rapid acquisition with a relaxation enhancement sequence as a fast T2-weighted imaging yields useful images for the morphologic diagnosis of ocular diseases, and MRI using a fast spoiled gradient-recalled-echo sequence as a T1-weighted imaging yields additional information by the administration of gadolinium-based contrast material for assessing the vascularity of intraocular tumors. These ocular imaging techniques are useful for the evaluation of patients with angle closure glaucoma, congenital abnormality of ocular globes, intraocular tumors and several types of detachments, as well as patients after ocular surgery. In this pictorial essay, we demonstrate the clinical applications of fast high-resolution ocular MRI with fixation of the subjects' visual foci.

Magnetic resonance imaging-determined subretinal fluid volume in an uveitic patient

PURPOSE

To describe the usefulness of the magnetic resonance imaging-determined subretinal fluid volume to evaluate the therapeutic effect on the retinal detachment caused by uveitis with the clouded media.

METHODS

We obtained the images by half-Fourier single-shot rapid acquisition with relaxation enhancement magnetic resonance imaging using a microscopy coil. We measured the area of subretinal fluid on each image and calculated the volume of subretinal fluid by multiplying the total area by the slice thickness.

RESULTS

A 56-year-old male who had lost his central visual field developed bullous retinal detachment in both eyes associated with uveitis. We treated him with steroid pulse therapy. We could not accurately evaluate the improvement of retinal detachment by ophthalmoscopy and ultrasonography as a result of the clouded media. We measured the volume of the subretinal fluid using magnetic resonance imagings. The volume of the subretinal fluid was observed to gradually decrease. These methods enable us to obtain clear magnetic resonance images within 2 seconds per slice. The reproducibility of the volumetry obtained by magnetic resonance imaging was excellent.

CONCLUSION

The adaptation of half-Fourier single-shot relaxation enhancement imaging performed with a surface coil makes it possible to evaluate the volumetry of a targeted space while also being useful for evaluating the effect of the treatment.

Optimal fast T2-weighted magnetic resonance microscopy imaging of the eye and its clinical application

PURPOSE

To compare a half-Fourier single-shot rapid acquisition with relaxation enhancement (RARE) sequence with a balanced steady-state free precession (b-SSFP) sequence in the evaluation of the eye using magnetic resonance (MR) microscopy imaging and to clarify the usefulness of RARE microscopy imaging in evaluating nonoperative glaucoma patients and patients who have undergone surgery for glaucoma or cataract.

MATERIALS AND METHODS

One-mm and 2-mm slice thickness images of RARE sequence and b-SSFP sequence using a 1.5 T MR unit and a 23-mm microscopy coil were obtained in eight healthy volunteers. The signal-to-noise (S/N) ratio of aqueous humor in the anterior chamber was measured quantitatively and visualization of the anterior chamber anatomy was assessed qualitatively. Furthermore, we evaluated 21 glaucoma patients (including six postoperative patients) and four patients after cataract surgery with 2-mm slice thickness RARE MRI.

RESULTS

The 2-mm slice thickness RARE imaging had a significantly greater S/N ratio than the 1-mm slice thickness RARE imaging (P < 0.05) and acquired the best image quality among the four types of images (P < 0.01). Additionally, 2-mm slice thickness RARE microscopy imaging could depict anterior chamber anatomy of glaucoma eyes and eyes after cataract surgery.

CONCLUSION

We believe that optimal fast T2-weighted MR microimaging might become a useful ophthalmologic examination technique.