Ultrasound prediction of follicle volume: is the mean diameter reflective?**Presented at the Conjoint Meeting of The American Fertility Society and the Canadian Fertility and Andrology Society, Montreal, Quebec, Canada, October 11 to 14, 1993

Three-Dimensional Automated Volume Calculation (Sonography-Based Automated Volume Count) versus Two-Dimensional Manual Ultrasonography for Follicular Tracking and Oocyte Retrieval in Women Undergoing in vitro Fertilization-Embryo Transfer: A Randomized Controlled Trial

Aim:

To compare the oocyte yield using three-dimensional (3D) automated and two-dimensional (2D) ultrasound-based follicle tracking in women undergoing in vitro fertilization-embryo transfer (IVF-ET).

Settings and Design:

A randomized controlled trial was conducted in the Reproductive Medicine Unit of a teaching medical institute from January 2017 to December 2018.

Materials and Methods:

A total of 130 patients undergoing IVF-ET were enrolled and randomized into two groups (65 patients in each group). In Group A, follicular tracking during controlled ovarian stimulation (COS) was done using 3D Sonography- based Automated Volume Count (SonoAVC), whereas in Group B, follicular tracking was done by manual ultrasonography (2D USG). The primary outcome measures were the number of oocytes retrieved (the total number and the number of mature oocytes). Secondary outcomes were fertilization rate, cleavage rate, total number of embryos and time taken to perform scans. Other outcome measures were clinical pregnancy rate, miscarriage rate and live birth rate (LBR).

Statistical Analysis Used:

Chi-square test, Student's t-test, Z-test, Wilcoxon rank-sum test, Bland–Altman's plot.

Results:

The two groups were comparable with regard to assisted reproductive technology (ART) outcomes. Group B required more time for performing the scan (P < 0.01).

Conclusion:

Automated SonoAVC ultrasound can be used interchangeably with manual 2D USG for follicle tracking during COS giving comparable ART outcomes with the added advantage of saving time. Our study implies the promising results of applying artificial intelligence in follicular tracking during COS.

From a circle to a sphere: the ultrasound imaging of ovarian follicle with 2D and 3D technology

Ultrasound follicular count (antral follicle count, AFC) is a necessary tool for measuring ovarian reserve, whereby the estimated number of follicles responsive to FSH can predict the number of oocytes retrieved in IVF cycles and may be the basis for individualized ovarian stimulation therapy. Advances in the ultrasound technology have recently lead to the improvement in resolution and quality of the image. Moreover the automatic measurements of follicular diameter by using some specific 3D software seems associated to several advantages when compared to the 2D technique. Examination time is reduced because the ultrasound scan data are stored and can be analyzed in detail at a later time. These data can be reconstructed in any plane, regardless of the original scan plane facilitating the detailed analysis. Another advantage is that this new technique reduces the operator's influence on scan interpretation and objectivity; therefore, interobserver variability is reduced. Using follicular volume obtained with sono AVC as the measure of follicular growth combined with volume-based criteria for the hCG triggering may in the future improve the treatment outcome compared to that achieved with conventional monitoring with follicular diameter. Better knowledge in this area could be helpful to optimize IVF outcome, by refining ovarian stimulation protocols and obtain high quality oocytes.

Fertility Treatment Outcomes After Follicle Tracking With Standard 2-Dimensional Sonography Versus 3-Dimensional Sonography-Based Automated Volume Count: Prospective Study

OBJECTIVES

The use of sonography-based Automated Volume Count (SonoAVC; GE Healthcare, Kretz, Zipf, Austria) leads to substantially lower intraobserver and interobserver variability with a considerable advantage in time gain for both the physician and patient. It offers the possibility of continuous training and standardization of follicular monitoring. Manual and automated follicular measurements during in vitro fertilization (IVF) are reported to be comparable during gonadotropin-releasing hormone (GnRH) agonist treatment. The aim of our study was to evaluate the effect of follicle tracking with 3-dimensional (3D) SonoAVC on treatment outcomes in GnRH antagonist IVF cycles.

METHODS

A prospective trial included 54 women undergoing their first to fourth GnRH antagonist IVF cycles. Follicle tracking from the initiation of ovarian stimulation until the day of oocyte retrieval and timing of oocyte retrieval was done either by conventional 2-dimensional (2D) sonography or 3D SonoAVC (open-labeled parallel assignment). In both groups, recombinant human chorionic gonadotropin was injected when there were at least 3 leading follicles measuring 17 mm. The primary outcome was the oocyte maturation rate, and secondary outcomes were the fertilization rate and clinical pregnancy rate.

RESULTS

The number of retrieved oocytes, number and rate of mature oocytes, fertilization rate, and clinical pregnancy rate were similar for 2D sonography and 3D SonoAVC. On a multivariate regression analysis, the use of 3D sonography was not a significant independent predictor of mature oocytes or clinical pregnancy rates.

CONCLUSIONS

Follicle tracking with 3D sonographic follicular volume measurements does not achieve better fertility outcomes than standard 2D sonography.

Relationship between follicular volume and oocyte competence, blastocyst development and live-birth rate: optimal follicle size for oocyte retrieval

OBJECTIVE

To analyze oocyte competence in gonadotropin-releasing hormone agonist (GnRHa) stimulation cycles with regard to maturity, fertilization and blastocyst rate, as well as clinical outcome (pregnancy and live-birth rate), in relation to follicular volume, measured by three-dimensional transvaginal sonography (3D-TVS), and follicular fluid composition.

METHODS

This was a prospective single-center study conducted between June 2012 and June 2014, including 118 ovum pick-ups with subsequent embryo transfer. Ovarian stimulation was performed using the GnRHa long protocol. Of 1493 follicles aspirated individually, follicular volume was evaluated successfully in 1236 using automated 3D-TVS during oocyte retrieval. Oocyte maturity and blastocyst development were tracked according to follicular volume. Intrafollicular concentrations of estradiol, testosterone, progesterone, luteinizing hormone, follicle-stimulating hormone and granulocyte-colony stimulating factor were quantified by immunoassay. Clinical outcome, in terms of implantation rate, (clinical) pregnancy rate, miscarriage and live-birth rate (LBR), was evaluated.

RESULTS

Follicles were categorized, according to their volume, into three arbitrary groups, which included 196 small (8-12 mm/0.3-0.9 mL), 772 medium (13-23 mm/1-6 mL) and 268 large (≥ 24 mm/> 6 mL) follicles. Although oocyte recovery rate was significantly lower in small follicles compared with medium and large ones (63.8% vs 76.6% and 81.3%, respectively; P < 0.001), similar fertilization rates (85.1% vs 75.3% and 81.4%, respectively) and blastocyst rates (40.5% vs 40.6% and 37.2%, respectively) per mature metaphase II oocyte were observed. A trend towards higher LBR after transfer of blastocysts derived from small (< 1 mL) follicles compared with medium (1-6 mL) or large (> 6 mL) follicles (54.5% vs 42.0%, and 41.7%, respectively) was observed. No predictive value of follicular fluid biomarkers was identified.

CONCLUSIONS

Our data indicate that the optimal follicular volume for a high yield of good quality blastocysts with good potential to lead to a live birth is 13-23 mm/1-6 mL. However, oocytes derived from small follicles (8-12 mm/0.3-0.9 mL) still have the capacity for normal development and subsequent delivery of healthy children, suggesting that aspiration of these follicles should be encouraged as this would increase the total number of blastocysts retrieved per stimulation. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

The association of follicular fluid volume with human oolemma stretchability during intracytoplasmic sperm injection

Objective

Oocyte degeneration often occurs after intracytoplasmic sperm injection (ICSI), and the risk factor is low-quality oocytes. The follicular fluid (FF) provides a crucial microenvironment for oocyte development. We investigated the relationships between the FF volume aspirated from individual follicles and oocyte retrieval, oocyte maturity, oolemma stretchability, fertilization, and development.

Methods

This retrospective study included data obtained from 229 ICSI cycles. Ovarian stimulation was performed according to a gonadotropin-releasing hormone antagonist protocol. Each follicle was individually aspirated and divided into six groups according to FF volume (<1.0, 1.0 to <2.0, 2.0 to <3.0, 3.0 to <4.0, 4.0 to <5.0, and ≥5.0 mL). Oolemma stretchability during ICSI was evaluated using a mechanical stimulus for oolemma penetration, that is, the stretchability was assessed by oolemma penetration with aspiration (high stretchability) or without aspiration (low stretchability).

Results

Oocyte retrieval rates were significantly lower in the <1.0 mL group than in the ≥1.0 mL groups (46.0% [86/187] vs. 67.5%–74.3% [172/255 to 124/167], respectively; p<0.01). Low oolemma stretchability was significantly more common in the <1.0 mL group than in the ≥1.0 mL groups during ICSI (22.0% [13/59] vs. 5.8%–9.4% [6/104 to 13/139], respectively; p=0.018). There was a relationship between FF volume and oolemma stretchability. However, there were no significant differences in the rates of fertilization, cleavage, ≥7 cells at day 3, and blastocyst development among all groups.

Conclusion

FF volume is potentially associated with the stretchability of metaphase II oolemma during ICSI. Regarding oolemma stretchability, ensuring a uniform follicular size during ovarian stimulation is crucial to obtain good-quality oocytes.

Follicular Volume Predicts Oocyte Maturity: A Prospective Cohort Study Using Three-Dimensional Ultrasound and SonoAVC

The aim of this study was to investigate whether the automatic measurement of follicular volume by three-dimensional (3D) ultrasound can predict the number of mature oocytes retrieved. A prospective cohort study including 47 women undergoing in vitro fertilization was conducted in a private fertility center. Follicular growth was monitored both manually and automatically using 3D scanning with SonoAVC on the day of human chorionic gonadotropin (hCG) administration. Regression analysis showed that under a standard protocol for hCG administration, the count of mature oocytes is well predicted by a multivariate model including the counts of follicles in the volume classes 2.00 to 5.00 cm³, 1.50 to 1.99 cm³, 1.00 to 1.49 cm³, and 0.60 to 0.99 cm³ In conclusion, this study shows that follicular volume as measured by SonoAVC on the day of hCG administration can be useful to predict oocyte maturity. Specifically, larger follicles and smaller size follicles (class 0.60-0.99 cm³) contribute to the mature oocyte count. This finding warrants the design of clinical trials to establish new criteria for hCG administration based on follicular volume.

Learning curves in 3-dimensional sonographic follicle monitoring during controlled ovarian stimulation

OBJECTIVES

Three-dimensional (3D) sonographically based automated volume calculation (SonoAVC; GE Healthcare, Zipf, Austria) is being introduced in folliculometry during ovarian stimulation; however, clear training assessments in this technique are lacking. The learning curve-cumulative summation (LC-CUSUM) test provides a quantitative tool to determine when a trainee has learned a procedure. The aim of this prospective study was to assess 3D SonoAVC LC-CUSUM curves in folliculometry.

METHODS

Analyses were performed on 98 oocyte donors by capturing the ovarian image in 3D and applying the 3D SonoAVC software during ovarian stimulation cycles. Each patient was scanned by an expert operator and by a trainee. Independent LC-CUSUM tests for 4 follicular diameters tracked the competency of 3 trainees in 3D SonoAVC.

RESULTS

We found that the numbers of sonographic examinations required by the 3 trainees to identify the correct number of follicles of 10 mm or larger were 38, 32, and 28, respectively; for follicles of 14 mm or larger, they were 29, 28, and 28; for follicles of 18 mm or larger, they were 24, 19, and 27; and for follicles of 21 mm or larger, they were 29, 19, and 24.

CONCLUSIONS

A variable number of procedures are needed to reach proficiency in 3D SonoAVC, even for trained 2-dimensional sonographers. Assessment of learning curves should be implemented when incorporating 3D SonoAVC in reproduction units.

[Ovarian stimulation monitoring: past, present and perspectives]

Since the inception of Assisted Reproductive Technology (ART), knowing the moment of ovulation has always been a priority. Initially, the monitoring was accomplished by observing the luteinizing hormone (LH) surge just before ovulation. Currently, in all ART facilities, the monitoring of all stimulated ovulatory cycles is done by using the conventional two-dimensional (2D) ultrasound to measure follicle diameter and by drawing blood tests that measure estradiol, progesterone, and luteinizing hormone levels. These exams allow determination of the numbers and quality of growing ovarian follicles and evaluation of follicle maturity before choosing the appropriate time for ovulation triggering. The monitoring of ovulatory cycles has now become enhanced with the arrival of new software called SonoAVC. This software allows the utilization of 3D blocks to immediately calculate the total number and volume of the follicles inside the ovary. This automatic approach is faster, precise, and more efficient. It also has better reproducibility than the classical 2D diameters. Furthermore, certain ART professionals envision that by using the SonoVac technology, patients will no longer need to be monitored with regular ultrasounds and with systematic hormonal testing.

Comparison of automated and manual follicle monitoring in an unrestricted population of 100 women undergoing controlled ovarian stimulation for IVF

BACKGROUND

Ovarian response to gonadotrophin stimulation is monitored with serial ultrasound (US) examinations. Sonography-based Automated Volume Count (SonoAVC) is a relatively new three-dimensional (3D) US technology, which automatically generates a set of measurements including the mean follicular diameter (MFD) and a volume-based diameter (d(V)) for each follicle in the ovaries. The present study aimed to assess the applicability and reproducibility of this automated follicle measurement method in an IVF programme.

METHODS

For this prospective method comparison study, 100 women undergoing US monitoring of a controlled ovarian stimulation cycle were recruited. Each follicle was manually measured by taking the mean of maximal diameters on three orthogonal planes with two-dimensional (2D) US. A 3D volume of each ovary was then captured. The ovarian volumes were later analysed using SonoAVC. The agreement between the two methods for the numbers of follicles and the size of the leading follicle was assessed with the Bland-Altman method. The reproducibility of SonoAVC measurements was assessed with the intraclass correlation coefficient (ICC).

RESULTS

Both SonoAVC-generated MFD and d(V)-based follicle counts, as well as the leading follicle diameter, had good agreement with conventional 2D US measurements. SonoAVC measurements had very good reproducibility, with ICC ≥0.8 for most evaluations.

CONCLUSIONS

Automated follicle monitoring with SonoAVC can replace or be used interchangeably with conventional 2D measurements. Automated follicle monitoring can save time, provide a method of quality control and create opportunities for developing HCG criteria based on follicular volume or for monitoring patients from a distance.

Automated follicle tracking improves measurement reliability in patients undergoing ovarian stimulation

This study tested the hypothesis that the automated assessment of a stimulated ovary, using 3D ultrasound and sono-AVC (automatic volume calculation), provides quicker analysis of follicular number and size than conventional 2D ultrasound, without any loss in measurement validity. Transvaginal ultrasound was performed on day 10 of stimulation in 89 prospectively recruited subjects undergoing IVF treatment. The number and mean diameter of follicles present in both ovaries was measured manually using 2D ultrasound. 3D data were then acquired and analysed using sono-AVC. Outcome measures included the number of follicles with a mean diameter >9 mm, >13 mm and >17 mm. The time taken for measurements and data acquisition was recorded. The two methods were compared using a paired t-test or the Wilcoxon signed rank test. Complete data were available for 82 subjects. There was no significant difference in the number of follicles with mean diameters >9 mm, >13 mm and >17 mm measured by either method. The total time taken for follicular measurements was significantly less (P < 0.01) for the automated 3D method (180.5 +/- 63.6 versus 236.1 +/- 57.1 s) which was associated with significantly less exposure to ultrasound (39.0 +/- 6.0 versus 236.10 +/- 57.1 s; P < 0.001). Automated 3D follicular measurements using sono-AVC provide a comparable but quicker assessment of follicle number and size.

Prospective cohort study of three- versus two-dimensional ultrasound for prediction of oocyte maturity

OBJECTIVE

To determine whether three-dimensional follicular ultrasound (3-D) measurements are better predictors of optimal timing of hCG administration than two-dimensional (2-D) images, the current standard.

DESIGN

Prospective, cohort study.

SETTING

Tertiary referral center.

PATIENT(S)

Seventy-six patients undergoing IVF.

INTERVENTION(S)

Seventy-six consecutive patients undergoing serial follicular monitoring during IVF had an additional daily 3-D volume scan of their ovaries once lead follicles had reached 16 mm diameter.

MAIN OUTCOME MEASURE(S)

Number of mature oocytes retrieved.

RESULT(S)

The 2-D follicular diameter measurements predicted 25.4% of the observed variance in the number of mature oocytes retrieved. The 3-D follicular volume measurements were more predictive of outcome, accounting for 29.2% of the observed variance in number of mature oocytes retrieved. Follicles >22 mm diameter and 5 mL volume were associated with fewer mature oocytes reflecting an undesired postmature state. Follicles measuring 11 to 15 mm had a 50% chance of yielding a mature oocyte.

CONCLUSION(S)

Three-dimensional follicular volume measurements have a stronger correlation with the number of mature oocytes retrieved than 2-D measurements. As 3-D technology improves, this parameter may replace 2-D measurements in the optimal timing of hCG before oocyte retrieval.

SonoAVC: a novel method of automatic volume calculation

OBJECTIVES

To assess the ability of the new software SonoAVC to measure follicular volume and to compare these volume calculations with those made by conventional methods.

METHODS

Three-dimensional ultrasound imaging was used to acquire volumetric data from the ovaries of 51 women undergoing controlled ovarian stimulation as part of in-vitro fertilization treatment. All assessments were performed on the day of oocyte retrieval and the true volume of each follicle was ascertained by manual measurement of the follicular aspirate. SonoAVC was used to automatically measure the volume of follicles and to provide three perpendicular diameters (xyz diameters), which were used to estimate volume using the sphere formula. The sphere formula was also used to estimate the volume from manual measurements of follicle diameter derived from conventional two-dimensional (2D) displays. Virtual Organ Computer-aided AnaLysis (VOCAL) was also used to measure volume, and the validity of each technique was compared using limits of agreement.

RESULTS

Two hundred and twenty-four follicles with a mean follicular volume of 3.7 (range, 0.4-16.2) cm(3) were studied. SonoAVC provided highly accurate automatic follicular volume measurements in all cases. Volume estimations made from the automatic maximal follicular diameter measurements (xyz diameters) were less valid. VOCAL proved highly valid but was less accurate than SonoAVC. Volumes estimated from manually derived follicular diameter measurements were the least accurate.

CONCLUSIONS

SonoAVC provides highly valid, automatic measurements of follicular volume. These measurements are more accurate than volumes estimated from 2D manual measurements, automated measurements of follicular diameter and those calculated using VOCAL.

Volume segmentation and reconstruction from freehand three-dimensional ultrasound data with application to ovarian follicle measurement

This article presents a semi-automatic method for segmentation and reconstruction of freehand three-dimensional (3D) ultrasound data. The method incorporates a number of interesting features within the level-set framework: First, segmentation is carried out using region competition, requiring multiple distinct and competing regions to be encoded within the framework. This region competition uses a simple dot-product based similarity measure to compare intensities within each region. In addition, segmentation and surface reconstruction is performed within the 3D domain to take advantage of the additional spatial information available. This means that the method must interpolate the surface where there are gaps in the data, a feature common to freehand 3D ultrasound reconstruction. Finally, although the level-set method is restricted to a voxel grid, no assumption is made that the data being segmented will conform to this grid and may be segmented in its world-reference position. The volume reconstruction method is demonstrated in vivo for the volume measurement of ovarian follicles. The 3D reconstructions produce a lower error variance than the current clinical measurement based on a mean diameter estimated from two-dimensional (2D) images. However, both the clinical measurement and the semi-automatic method appear to underestimate the true follicular volume.

Measurement of the speed of sound in follicular fluid

BACKGROUND

Measurement of ovarian follicles by ultrasound is common practice in fertility treatment. However, the effect of the speed of sound is not taken into account. We present results from a study aimed at measuring this.

METHODS

The speed of sound was measured in samples of follicular fluid aspirated from patients undergoing fertility treatment. The transmitted and received pulses from a single element ultrasound transducer were recorded using a digital oscilloscope for a pulse passed through a sample of the fluid. The distance over which the pulse travelled was known from calibration with pure water. Variation with temperature was investigated in the range 25-45 degrees C. Dependence on ultrasound frequency, patient and time from aspiration were also investigated.

RESULTS

The speed of sound in follicular fluid was found to be 1550+/-3 m/s at 37.3 degrees C using 5.0 MHz ultrasound. The speed varied from 1528+/-3 m/s at 24.8 degrees C to 1561+/-3 m/s at 44.8 degrees C. Variation with patient, time and frequency were not detected.

CONCLUSION

The speed of sound in follicular fluid at body temperature is 1550 m/s. This small difference from the speed assumed by the ultrasound machine corresponds to the systematic bias in volume measurement evident in previously published results.

One, two or three: how many directions are useful in transvaginal ultrasound measurement of ovarian follicles?

OBJECTIVE

To investigate whether it is necessary to measure an ovarian follicle in three directions using transvaginal ultrasonography.

METHODS

In 36 healthy female volunteers transvaginal ultrasonography was performed every other day during a spontaneous menstrual cycle. The diameter of the largest follicle in each ovary was measured in two directions in the sagittal plane, and in two directions in the coronal plane. In total, 304 follicular measurements were performed. The largest follicular diameter was compared to the mean diameter of two and three directions, respectively. The mean diameter of two directions was compared to that of three directions.

RESULTS

The mean difference between measurement in one and two directions was 1.2 mm (standard deviation (S.D.) = 1.1 mm), between measurement in one and three directions 1.2 mm (S.D. = 1.0 mm), and between measurement in two and three directions -0.03 mm (S.D. = 0.3 mm). The mean difference and the standard deviation of the difference increased with the follicular diameter.

CONCLUSIONS

In non-stimulated menstrual cycles, follicle measurement in only one direction is less accurate than measurement in two and three directions, and may result in clinically relevant differences. However, measurement in three directions gives no additional information compared to measurement in two directions.

Comparison of follicle steroidogenesis from normal and polycystic ovaries in women undergoing IVF: relationship between steroid concentrations, follicle size, oocyte quality and fecundability

Studies of ovarian stimulation for IVF have suggested a relationship between follicle size and pregnancy rates. Furthermore the follicular endocrine environment is correlated with oocyte quality. The aim of this study was first to verify the relationship between follicular steroid content, follicular size, oocyte maturity and fertilization outcome in women with normal ovaries following recombinant human FSH (rhFSH). Secondly this study was extended to women with polycystic ovarian syndrome (PCOS). Fifty-nine patients (31 normal, 28 PCOS) underwent conventional IVF with rhFSH induction. Follicular diameter was classified as small (8-13 mm) or large (>14 mm) and sex steroid content was analysed for each group. Oocyte maturity was studied according to nuclear maturation the day after fertilization. In both ovulation groups, 17 beta-oestradiol and progesterone concentration were significantly higher in large follicles with meiotically competent oocytes compared with those containing meiotically incompetent oocytes. Testosterone levels were increased in PCOS follicles compared with normal patients, with no difference between corresponding sub-groups of follicles with meiotically competent oocytes. The relationship between follicle size and embryo development showed that 14 mm could be a threshold value following rhFSH induction in normal or PCOS women.

Measurements of organ volume by ultrasonography

In a clinical context, measurements of organ volume are often performed in the diagnosis and follow-up of patients with a variety of diseases. Ultrasonography is a cheap, widely available and non-hazardous imaging modality to use for estimation of volumes, and a range of two- and three-dimensional methods have emerged to accomplish this task. This paper reviews some of the ultrasound methods available in cardiology, gastroenterology, nephrology/urology and gynaecology/obstetrics. Using two-dimensional (2D) ultrasound, the simplest method of calculating the volume of an organ is based on the multiplication of three diameters perpendicular to each other. These 2D methods are often based on geometrical assumptions which may introduce significant errors in volume estimation. Therefore, volume estimation based on three-dimensional (3D) ultrasound has been developed to increase accuracy and precision. At present, the process of making 3D images based on ultrasonography is divided into five steps: data acquisition, data digitization, data storage, data processing and data display. In conclusion, ultrasonography is a useful and reliable tool to calculate volumes of organs. In particular, 3D ultrasonography seems promising in this respect and appears to be superior to 2D ultrasonography in accuracy and precision in volume measurements.

Ovarian ultrasound image analysis: follicle segmentation

Ovarian ultrasound is an effective tool in infertility treatment. Repeated measurements of the size and shape of follicles over several days are the primary means of evaluation by physicians. Currently, follicle wall segmentation is achieved by manual tracing which is time consuming and susceptible to inter-operator variation. An automated method for follicle wall segmentation is reported that uses a four-step process based on watershed segmentation and knowledge-based graph search algorithm which utilizes priori information about follicle structure for inner and outer wall detection. The automated technique was tested on 36 ultrasonographic images of women's ovaries. Validation against manually traced borders has shown good correlation of manually defined and computer-determined area measurements (R2 = 0.85 - 0.96). The border positioning errors were small: 0.63+/-0.36 mm for inner border and 0.67+/-0.41 mm for outer border detection. The use of watershed segmentation and graph search methods facilitates fast, accurate inner and outer border detection with minimal user-interaction.