Evaluation of a technique for estimation of extraocular muscle volume using 2D MRI

Computed tomography and magnetic resonance imaging approaches to Graves' ophthalmopathy: a narrative review

Graves' ophthalmopathy (GO) affects up to 50% of patients with Graves' disease (GD) ranging from mild ocular irritation to vision loss. The initial diagnosis is based on clinical findings and laboratory tests. Orbital imaging, such as magnetic resonance imaging (MRI) and computed tomography (CT), is an important tool to assess orbital changes, being also useful for understanding disease progression and surgical planning. In this narrative review, we included 92 studies published from 1979 to 2020 that used either MRI and/or CT to diagnose and investigate GO, proposing new methods and techniques. Most of the methods used still need to be corroborated and validated, and, despite the different methods and approaches for thyroid eye disease (TED) evaluation, there is still a lack of standardization of measurements and outcome reports; therefore, additional studies should be performed to include these methods in clinical practice, facilitating the diagnosis and approach for the treatment of TED.

Deep-Learning-Based Segmentation of Extraocular Muscles from Magnetic Resonance Images

In this study, we investigated the performance of four deep learning frameworks of U-Net, U-NeXt, DeepLabV3+, and ConResNet in multi-class pixel-based segmentation of the extraocular muscles (EOMs) from coronal MRI. Performances of the four models were evaluated and compared with the standard F-measure-based metrics of intersection over union (IoU) and Dice, where the U-Net achieved the highest overall IoU and Dice scores of 0.77 and 0.85, respectively. Centroid distance offset between identified and ground truth EOM centroids was measured where U-Net and DeepLabV3+ achieved low offsets (p > 0.05) of 0.33 mm and 0.35 mm, respectively. Our results also demonstrated that segmentation accuracy varies in spatially different image planes. This study systematically compared factors that impact the variability of segmentation and morphometric accuracy of the deep learning models when applied to segmenting EOMs from MRI.

Semantic Segmentation of Extraocular Muscles on Computed Tomography Images Using Convolutional Neural Networks

Computed tomography (CT) imaging of the orbit with measurement of extraocular muscle size can be useful for diagnosing and monitoring conditions that affect extraocular muscles. However, the manual measurement of extraocular muscle size can be time-consuming and tedious. The purpose of this study is to evaluate the effectiveness of deep learning algorithms in segmenting extraocular muscles and measuring muscle sizes from CT images. Consecutive CT scans of orbits from 210 patients between 1 January 2010 and 31 December 2019 were used. Extraocular muscles were manually annotated in the studies, which were then used to train the deep learning algorithms. The proposed U-net algorithm can segment extraocular muscles on coronal slices of 32 test samples with an average dice score of 0.92. The thickness and area measurements from predicted segmentations had a mean absolute error (MAE) of 0.35 mm and 3.87 mm², respectively, with a corresponding mean absolute percentage error (MAPE) of 7 and 9%, respectively. On qualitative analysis of 32 test samples, 30 predicted segmentations from the U-net algorithm were accepted while 2 were rejected. Based on the results from quantitative and qualitative evaluation, this study demonstrates that CNN-based deep learning algorithms are effective at segmenting extraocular muscles and measuring muscles sizes.

Extraocular Muscle Volumetry for Assessment of Thyroid Eye Disease

BACKGROUND

In this study we evaluate the diagnostic accuracy of extraocular muscle volumetry in detecting thyroid eye disease and to compare the results with simple measurements of maximal medial rectus (MR) diameter.

METHODS

Cross-sectional study that included 47 eyes of 47 patients with thyroid eye disease and 47 healthy controls. Patients underwent slitlamp examination and imaging consisting of computed tomography scans. Image segmentation and volume measurements were performed by 2 independent researchers. Intraobserver and interobserver reliability testing was also conducted.

RESULTS

Total extraocular muscle volume was 7.31 ± 1.88 cm3 and medial volume was 2.38 ± 0.73 cm3 in the study group. In this group, the maximum measured diameter of the MR was 6.67 ± 0.35 mm. MR volume was statistically associated with maximum MR diameter (r = 9.78; P < 0.001). Both MR volume and maximum MR diameter measurements showed good predictive efficacy as shown using receiver operator characteristic curve analysis.

CONCLUSIONS

Complications of thyroid eye disease are often sight threatening, and timely diagnosis is crucial for the management of the entity and its sequelae. The results of this study imply that simple measurements of maximum MR diameter are sensitive enough to establish diagnosis.

Extraocular muscle sampled volume in Graves' orbitopathy using 3-T fast spin-echo MRI with iterative decomposition of water and fat sequences

Background

Current magnetic resonance imaging (MRI) techniques for measuring extraocular muscle (EOM) volume enlargement are not ideally suited for routine follow-up of Graves’ ophthalmopathy (GO) because the difficulty of segmenting the muscles at the tendon insertion complicates and lengthens the study protocol.

Purpose

To measure the EOM sampled volume (SV) and assess its correlation with proptosis.

Material and Methods

A total of 37 patients with newly diagnosed GO underwent 3-T MRI scanning with iterative decomposition of water and fat (IDEAL) sequences with and without contrast enhancement. In each patient, the three largest contiguous coronal cross-sectional areas (CSA) on the EOM slices were segmented using a polygon selection tool and then summed to compute the EOM-SV. Proptosis was evaluated with the Hertel index (HI). The relationships between the HI value and EOM-SV and between HI and EOM-CSA were compared and assessed with Pearson’s correlation coefficient and the univariate regression coefficient. Inter-observer and intra-observer variability were calculated.

Results

HI showed a stronger correlation with EOM-SV (P < 0.001; r = 0.712, r²= 0.507) than with EOM-CSA (P < 0.001; r = 0.645 and r²= 0.329). The intraclass correlation coefficient indicated that the inter-observer agreement was high (0.998). The standard deviation between repeated measurements was 1.9–5.3%.

Conclusion

IDEAL sequences allow for the measurement EOM-SV both on non-contrast and contrast-enhanced scans. EOM-SV predicts proptosis more accurately than does EOM-CSA. The measurement of EOM-SV is practical and reproducible. EOM-SV changes of 3.5–8.3% can be assumed to reflect true volume changes.

Changes in Extraocular Muscle Volume During Ocular Duction

Purpose

It has been tacitly assumed that overall extraocular muscle (EOM) volume is conserved during contraction and relaxation, yet this assumption has been untested up to now. We used high-resolution magnetic resonance imaging (MRI) to determine if total EOM volume changes during relaxation and contraction.

Methods

Surface coil MRI in quasi-coronal planes was obtained in target-controlled, maximal secondary gaze positions in 30 orbits of 15 normal subjects at 312-μm resolution. Ductions were quantified by changes in globe-optic nerve positions. Cross-sections of EOM were manually outlined in contiguous image planes so that volumes could be calculated by multiplying summed cross sections by the 2-mm slice thickness. Three-dimensional reconstruction allowed measurement of the lengths of terminal, unresolvable EOM segments, providing estimates of terminal EOM volumes to be summed with measured midorbital volumes to obtain total EOM volumes.

Results

Duction range averaged 44.3 ± 4.8° from relaxation to contraction. There was a significant increase in total volume in each rectus EOM from relaxation to contraction: superior rectus (SR) 92 ± 36 mm³ (+18%, P < 10⁻¹¹); inferior rectus (IR) 51 ± 18 mm³ (+9%, P < 10⁻¹¹); medial rectus (MR) 78 ± 36 mm³ (+11%, P < 10⁻⁵); and lateral rectus (LR) 47 ± 45 mm³ (+7%, P = 0.005). Because volume changes for SR and MR exceed IR and LR, total rectus EOM volume increases in supraduction 41 ± 42 mm³ (+3.7%) and adduction 32 ± 63 mm³ (+2.3%).

Conclusions

Total EOM volume is not conserved but instead increases with contraction and decreased with relaxation. Contractile volume increases may be secondary to increased actin-myosin lattice spacing, so that density decreases. This effect is opposite that of possible hemodynamic changes.

Correlation between Extraocular Muscle Size Measured by Computed Tomography and the Vertical Angle of Deviation in Thyroid Eye Disease

The aim of this study was to investigate extraocular muscle (EOM) volume and cross-sectional area using computed tomography (CT), and to determine the relationship between EOM size and the vertical angle of deviation in thyroid eye disease (TED). Twenty-nine TED patients (58 orbits) with vertical strabismus were enrolled in the study. All patients underwent complete ophthalmic examination including prism, alternate cover, and Krimsky tests. Orbital CT scans were also performed on each patient. Digital image analysis was used to quantify superior rectus (SR) and inferior rectus (IR) muscle cross-sectional areas and volumes. Measurements were compared with those of controls. The correlation between muscle size and degree of vertical angle deviation was evaluated. The mean vertical angle of deviation was 26.2 ± 4.1 prism diopters. The TED group had a greater maximum cross-sectional area and EOM volume in the SR and IR than the control group (all p<0.001). Area and volume of the IR were correlated with the angle of deviation, but the SR alone did not show a significant correlation. The maximum cross-sectional area and volume of [Right IR + Left SR − Right SR − Left IR] was strongly correlated with the vertical angle of deviation (P<0.001). Quantitative CT of the orbit with evaluation of the area and volume of EOMs may be helpful in anticipating and monitoring vertical strabismus in TED patients.

Magnetic resonance imaging of skeletal muscle disease

Neuromuscular diseases often exhibit a temporally varying, spatially heterogeneous, and multifaceted pathology. The goals of this chapter are to describe and evaluate the use of quantitative magnetic resonance imaging (MRI) methods to characterize muscle pathology. The following criteria are used for this evaluation: objective measurement of continuously distributed variables; clear and well-understood relationship to the pathology of interest; sensitivity to improvement or worsening of clinical status; and the measurement properties of accuracy and precision. Two major classes of MRI methods meet all of these criteria: (1) MRI methods for measuring muscle contractile volume or cross-sectional area by combining structural MRI and quantitative fat-water MRI; and (2) an MRI method for characterizing the edema caused by inflammation, the measurement of the transverse relaxation time constant (T2). These methods are evaluated with respect to the four criteria listed above and examples from neuromuscular disorders are provided. Finally, these methods are summarized and synthesized and recommendations for additional quantitative MRI developments are made.

Morphometric parameters of extraocular rectus muscles evaluated by dynamic-multipositional magnetic resonance

PURPOSE

To establish normal values of morphologic parameters of extraocular rectus muscles visualized in different gaze positions by means of an accessible method of dynamic-multipositional magnetic resonance imaging (dmMRI).

METHODS

Twenty eyes of 10 healthy, orthotropic subjects were examined. A 1.5T scanner (Avanto) with standard head coil was used. The protocol of dmMRI included 6 gaze positions in 10° intervals in which 13-second, orbital, T2 sequences were performed in quasi-coronal plane. The measurements of extraocular rectus muscles shape, sectional area, and volume were obtained with use of ImageJ 1.38x (NIH) software.

RESULTS

Relative change in cross-sectional area between position of rest and gaze of action of each muscle appears to be significant just in the medial and posterior parts of their belly. The maximal cross-section area increases significantly when the muscle contracts (21% to 32% depending on the muscle). The superior rectus must be assessed along with levator palpebrae as the distinction between their bellies is difficult. Relative change in partial muscle volume on contraction ranged from 12.3% to 21.6% depending on the muscle. Muscle contraction results in more circular shape of its belly while relaxation is more of an ellipse.

CONCLUSIONS

Dynamic-multipositional MRI performed in the proposed manner is an accessible and repeatable method for visualization of extraocular rectus muscles. Assessment of morphometric parameters such as muscle shape, maximal cross-section area, and partial muscle volume is easy with digital imaging software.

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.

Differential involvement of orbital fat and extraocular muscles in graves' ophthalmopathy

Graves' ophthalmopathy (GO) is characterized by swelling of orbital fat and extraocular muscles, but little attention has been given to differential involvement of fat and muscles. Advancements in imaging allow rather accurate measurements of orbital bony cavity volume (OV), fat volume (FV) and muscle volume (MV), and are the topics of this review. Ratios of FV/OV and MV/OV neutralize gender differences. In adult Caucasian controls, mean values ± SD of FV/OV are 0.56 ± 0.11 and of MV/OV are 0.15 ± 0.02. FV increases substantially and MV decreases slightly with advancing age, requiring age-specific reference ranges. In 95 consecutive untreated Caucasian GO patients, both FV and MV were within normal limits in 25%, increased FV but normal MV was present in 5%, normal FV but increased MV was detected in 61%, and both increased FV and MV was evident in 9%. Increased FV was associated with more proptosis and longer GO duration. Increased MV was associated with older age, more severe GO (more proptosis and diplopia, worse eye muscle ductions), higher TBII and current smoking. At the cellular and molecular level differential involvement of fat and muscles might be related to differences between fibroblast phenotypes and cytokine profiles in each compartment, to different orbital T cell subsets during the course of the disease and to peroxisome proliferator activator receptor-γ polymorphisms and modulation of 11β-hydroxysteroid dehydrogenase-1. Enlarged muscles are apparently a rather early phenomenon in GO, whereas increases in fat mass occur relatively late. Why a minor subset of GO patients presents with an increase of only fat remains poorly understood.

A quantitative method for assessing the degree of axial proptosis in relation to orbital tissue involvement in Graves' orbitopathy

PURPOSE

To define a method of quantifying axial proptosis in patients with Graves' orbitopathy (GO) and to validate a score that correlates with the orbital involvement and helps determine the degree of proptosis correction for elective orbital decompression.

DESIGN

Retrospective, case series.

PARTICIPANTS

The study included 50 patients (group A) and 29 control subjects who underwent orbital computed tomography (CT). The method was then validated in another group of 21 patients with GO (group B).

METHODS

The orbital area (OA) was measured manually on the central axial section of the CT scan at a level where the lens is visualized. The OA intersects the projection of the globe and delimitates the chord of an arch (globe chord [OC]). The area of the circular sector under the chord (CA) represents the portion of the globe within the orbit.

MAIN OUTCOME MEASURES

A CA-to-OA ratio was calculated to reduce the error due to variability of the measurements and to perform correlations with some of the clinical parameters of GO.

RESULTS

Measurement error was low (<2%). We did not observe significant differences in the mean OA of patients with GO (783.6 ± 12.1 mm(2)) and controls (758.5 ± 20.4 mm(2); P = not significant). The OC value in patients with GO was 130.2 ± 11.5 mm(2), significantly lower than in controls (281.8 ± 9.7 mm(2); P<0.0001). The CA-to-OA ratio also was lower in patients with GO than in controls (0.16 ± 0.01 vs. 0.38 ± 0.01; P<0.0001). A significant correlation was found in patients with GO between the CA-to-OA ratio and proptosis (P<0.001), lid fissure (P = 0.004), and intraocular pressure (P<0.001). In group B, the CA-to-OA ratio was 0.18 ± 0.02, significantly different from that of controls (P<0.0001) and inversely correlated with proptosis (P<0.0001) and lid fissure (P<0.045).

CONCLUSIONS

By measuring the CA-to-OA ratio, we were able to quantify the degree of axial proptosis in patients with GO. The significant correlation of CA/OA with some orbital parameters confirms that this parameter also may be used as a measure of orbital involvement in GO.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Estimation of preoperative uterine weight in uterine myoma and uterine adenomyosis

INTRODUCTION

Uterine myoma and uterine adenomyosis frequently occur in sexually mature women. Total hysterectomy is the treatment of choice when the symptoms are severe. To select an operative procedure from abdominal, vaginal, and laparoscopic methods, precise estimation of the preoperative uterine weight is desired. In this study, we estimated the preoperative uterine weight with preoperative images in cases of uterine myoma and uterine adenomyosis.

METHODS

We evaluated 403 patients with uterine myoma or uterine adenomyosis (uterus < 1000 g) between 1996 and 2010. All patients underwent a preoperative MRI and received a hysterectomy with the uterine weight recorded. Based on MR images, we measured (in centimeters) the maximum longitudinal diameter in the sagittal section (a), the maximum lateral diameter (b) and the maximum longitudinal diameter in the transverse section (c) of each uterus. A correlation coefficient was calculated between the weight of the removed uterus and the value of a × b × c for each individual uterus. Also, a regression analysis was performed between x (the value of a × b × c) and y (weight of the removed uterus).

RESULTS

A strong correlation was shown between the weight of the removed uterus and the value of a × b × c (r = 0.81, P < 0.01). As a result of the regression analysis, the regression equation y = 0.35x + 107 (R(2) = 0.66, P < 0.01) was obtained.

CONCLUSION

In this study, the estimated weight of the uterus was calculated by the formula y = 0.35x + 107 (x = a × b × c), and this could be the determining factor in choosing a surgical method for hysterectomy.

Isolated lateral rectus muscle involvement as a presenting sign of euthyroid Graves disease

A 27-year-old man who presented with diplopia and proptosis and was diagnosed with euthyroid Graves disease and restrictive strabismus. It was determined that his symptoms were caused by isolated lateral rectus muscle involvement. Diplopia resolved and ocular motility improved substantially following 6 weeks of oral corticosteroid therapy.

Radiologic measurement of extraocular muscle volumes in patients with Graves' orbitopathy: a review and guideline

OBJECTIVE

To evaluate and compare techniques for extraocular muscle (EOM) volume measurement and to provide guidelines for future measurements.

DESIGN

Systematic review.

RESULTS

Existing techniques used to measure extraocular muscle volumes on radiologic scans can be divided into manual outlining, computer assisted and automated segmentation. Both computed tomography (CT) and magnetic resonance (MR) image datasets can be used. On CT scans, one best measures muscle volume using region grow segmentation, accepting an overestimation of true volume by inevitable inclusion of non-muscular tissue. On high resolution MRI scans, single muscles can be outlined manually, but measurements include only part of the muscle due to poor tissue contrast at the orbital apex. Measurement errors can be reduced 3.5% by exact horizontal repositioning. A measured volume change of at least 6-17% is required to demonstrate a significant difference.

CONCLUSION

Currently the best choice for EOM volume measurements on CT images is computer assisted grey value segmentation and on MRI images is manual outlining of individual muscles. Because of the time required and the complexity of the measurements, present EOM volume measurement is as yet only suitable for research purposes.

Superior oblique muscle involvement in thyroid ophthalmopathy

BACKGROUND

Rectus muscle involvement in thyroid ophthalmopathy is well documented. The inferior rectus is the most frequently involved, followed by the medial, superior, and infrequently the lateral rectus. This study reports involvement of the superior oblique muscle as a contributory cause of restrictive strabismus in patients with thyroid ophthalmopathy.

METHODS

This is a retrospective review of four patients with known thyroid ophthalmopathy who presented with incomitant vertical strabismus, A-pattern, overdepression in adduction, underelevation in adduction, and incyclotorsion. All patients underwent preoperative orbital imaging. Two of the four patients had previous orbital decompressions. All patients underwent surgery on the SO muscle.

RESULTS

Preoperative scans showed enlargement of one or both SO muscles in all patients and intraoperative forced duction testing revealed restriction to elevation in adduction in all cases. Preoperative A-pattern ranged from to 6 to 22 prism diopters. All subjects had preoperative incyclotorsion, ranging from 2 and 14 degrees. Improvement of the versions, hypertropia, and cyclotorsion followed surgical weakening procedures on the SO muscle.

CONCLUSION

Thyroid ophthalmopathy may involve the SO muscle. Clinical manifestations include preoperative A-pattern strabismus, incyclotorsion, and restrictive limitation to elevation in adduction. Orbital imaging documents SO muscle enlargement. Awareness of SO involvement in thyroid ophthalmopathy assists the surgeon to develop a more precise surgical strategy to correct the hypotropia.

Volume changes in intra- and extraorbital compartments in patients with Graves' ophthalmopathy: effect of smoking

The objective of this study was to demonstrate the effect of smoking history on soft tissue expansion in specific orbital compartments in patients with Graves' ophthalmopathy. The volumes of the rectus muscles, intra and extraorbital connective, and soft tissues were measured in 110 orbits of 35 patients and 20 control subjects. Data sets from current smokers, ex-smokers, and non-smokers were compared. The total number of cigarettes smoked was calculated, and it was used as an estimate for the severity of smoking (cumulative smoking). The volume measurements were performed on T1-weighted contiguous transversal magnetic resonance images of the orbits. Connective tissue volumes were influenced by smoking history, while muscle volumes were not affected. Ex-smokers had larger amount of extraorbital connective tissue than current smokers (p = 0.012), and this volume showed a good correlation with the number of cigarettes smoked (r = 0.539, p < 0.05). In current smokers, the amount of intraorbital connective tissue correlated well with the cumulative smoking (r = 0.635, p < 0.001). We conclude that connective tissue volumes in certain orbital compartments correlate well with cumulative smoking. Extraocular muscle volumes are not influenced by smoking in patients with Graves' ophthalmopathy.

A new MRI method for the quantitative evaluation of extraocular muscle size in thyroid ophthalmopathy

In cross section, extraocular muscles are more or less elliptical, with short and long diameters. We studied the ratio (R) of short to long diameter and investigated its use in quantitative assessment of the extraocular muscles in patients with Graves's disease. We measured the diameters on T1-weighted axial and coronal MRI and computed R for each extraocular muscle in 80 patients without and 40 with Graves's disease. We compared the measurements and R of the right and left orbits, and of men and women. The short diameter of all extraocular muscles apart from the superior oblique showed significant differences between men and women, and that of the inferior rectus varied significantly with age. R, however, was unrelated to sex or age. All patients with Graves's disease and an increased short diameter also had an increased R, but 6% of the muscles showed an increase in R, even though their short diameter was within the normal range.

Using morphologic parameters of extraocular muscles for diagnosis and follow-up of Graves' ophthalmopathy: diameters, areas, or volumes?

OBJECTIVE

The objective of this study was to find the most appropriate, accurate, and convenient muscle parameter that can be used as a substitute for volume in monitoring the effectiveness of therapy of patients with Graves' ophthalmopathy.

SUBJECTS AND METHODS

The four rectus muscles in 110 orbits (35 patients and 20 control subjects) were evaluated with MR imaging. The diameter at the largest extent of the muscle belly, as well as the long and the short diameters and the cross-sectional areas in a preselected coronal scan, were measured for each muscle and were compared with the corresponding muscle volume measured on contiguous T1-weighted transverse slices.

RESULTS

The measured coronal area correlated well with the volume of the superior (r = 0.694, p < 0.0001) and inferior (r = 0.783, p < 0.0001) recti, and the largest transverse diameter showed strong correlation with the volume of the lateral (r = 0.868, p < 0.0001) and medial (r = 0.869, p < 0.0001) recti. For the latter muscle, the coronal area also exhibited a good correlation with the volume (r = 0.838, p < 0.0001). Coronal cross-sectional areas can be well estimated by measuring both the short and long coronal muscle diameters (r values were between 0.914 and 0.966; p < 0.0001).

CONCLUSION

In Graves' ophthalmopathy, the volume of three of the rectus muscles can be well estimated by simple measurements on a single coronal slice, and the largest transverse diameter of the lateral rectus is suitable for the same purpose.

Graves ophthalmopathy

Graves ophthalmopathy (GO) is an autoimmune disease that typically affects the thyroid gland and the orbit. The roles of the thyroid stimulating hormone receptor and cellular and humoral immunity in the pathogenesis of GO are being investigated. Investigators are gaining insights into the epidemiology of GO as it relates to other ocular and autoimmune diseases. Several possible tools for assessing GO disease activity are being studied. Medical and radiation therapy for GO recently have been evaluated prospectively. Orbital surgeons continue to refine orbital decompression techniques to improve patient outcomes and minimize surgical complications.

Measuring extraocular muscle volume using dynamic contours

The effect of medical treatment on extraocular muscle enlargement in thyroid associated ophthalmopathy (TAO) may be monitored by measuring the change in volume of the extraocular muscles on serial orbital MRI examinations. In theory, 3D image sets offer the opportunity to minimise errors due to poor repositioning and partial volume effects. This study describes an automated technique for estimating extraocular muscle volumes from 3D datasets. Operator input is minimal and the technique is robust. Verification of the technique on both simulated and real datasets is described. For simulated image sets, both automated segmentation and manual outlining produced estimates of volume which were on average 4% less than "true" volume. For real patient data, extraocular muscle volumes measured by the automated technique were 1.6% (SD 13%) less than volumes measured by manual outlining. Coefficient of variation for repeat outlining of the same image dataset for the automated technique was 1.0%, compared with 4% for manual outlining. The manual technique took an experienced operator approximately 20 min to perform, compared to 7 min for the automated technique. The automated method is therefore rapid, reproducible and at least as accurate as other available methods.