13:30
Soft Tissue & Abdominal Organs
Chair: Linda Wauben
13:30
15 mins
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3D Ultrasound Strain Imaging of the Puborectalis Muscle
Shreya Das, Hendrik H.G. Hansen, Frieda van den Noort, C. Huub van der Vaart, Chris L. de Korte
Abstract: ABSTRACT
Female pelvic floor muscles provide support by compensating for gravity and abdominal pressure. During delivery some of them have to stretch up to three times their original length to allow for the passage of the baby. Frequently these muscles (for example, the puborectalis muscle or PRM) get damaged during childbirth, which can lead to irreversible damage. Due to this damage, women may suffer from disorders like pelvic organ prolapse or urinary and fecal incontinence [1-2]. 3D ultrasound (US) imaging can be used to image these muscles and detect the most severe cases of muscle damage. However, diagnosis of the damage is currently done in static images obtained from the US movies, which is observer dependent and not reproducible [3]. Our hypothesis is that by US-based strain imaging the exact deformation and motion of these muscles can be quantified which will aid in diagnosing muscle failure and allow a patient specific treatment strategy.
Transperineal 3D ultrasound movies were obtained from female volunteers (n=9) at 12 weeks of their first pregnancy, using a curved array volume transducer connected to a GE Voluson V730 US machine at the University Medical Centre, Utrecht, The Netherlands. Volumetric DICOM US data were acquired of the PRM starting at rest and via, contraction and relaxation by Valsalva maneuver, back to rest again. Displacements were estimated in 3D using a normalized coarse-to-fine cross-correlation-based algorithm [4]. All displacements were calculated with respect to a reference frame chosen in rest just before contraction. Displacements were calculated for a manually segmented region of interest (ROI) corresponding to the PRM [5]. Finally, axial strains were calculated using a 3D Least Squares Strain Estimator (LSQSE) [4, 6].
Preliminary results, show that axial strains of the PRM produces negative and positive strain values at contraction and Valsalva, respectively. Future studies in multiple volunteers will have to explore the reproducibility of our method and investigate if strain imaging can be used to quantify damage of the PRM. Furthermore, it is also being investigated if strain accuracy can be improved by incorporating tracking, implying the reference frame and ROI for displacement calculation is being updated frame by frame during the performance of the rest-contraction-Valsalva-rest procedure and strain is accumulated afterwards.
References:
[1] Bedretdinova D., et al.; Eur Urol 69(2):256-64, 2016.
[2] Dieter AA, et al.; Curr Opin Obstet Gynecol 27(5):380-4, 2015.
[3] van Veelen GA., et al.; Int Urogynecol J 25(11):1501-6, 2014.
[4] Hendriks, GAGM, et al.; Phys Med Biol 61(7):2665-79, 2016.
[5] van den Noort, F, et al.; Ultrasound Obstet Gynecol, epub ahead of print, 2017.
[6] Kallel F, et al.; Ultrason Imaging 19(3):195-208, 1997.
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13:45
15 mins
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Quantitative Ultrasound Imaging and Characterization of Uterine Peristaltic Waves
Yizhou Huang, Federica Sammali, Celine Blank, Nienke Kuijsters, Chiara Rabotti, Dick Schoot, Massimo Mischi
Abstract: Uterine peristalsis (UP) plays an important role in the generation of intrauterine streams; upstream towards the ovaries to support conception and downstream to favor menstrual emptying. Our understanding of the uterine mechanical behavior is however hampered by a lack of quantitative analysis, limiting identification and treatment of uterine dysfunctions. Building on our recent work on dedicated speckle tracking for uterine strain analysis, here we present the first algorithm for spatiotemporal assessment of UP.
In particular, we aim at characterizing the propagation of contraction waves along the uterus. Eleven women were scanned with B-mode transvaginal ultrasound during the late follicular phase, which coincides with the fertile period and is known to be the most active phase [1]. The speckle was tracked on the gray-level videos by optical flow. The method accuracy was further improved by an adaptive spatial-warping approach. The method was first optimized and validated with a dedicated setup producing controlled motion of an ex-vivo uterus [2]. In vivo, a grid of points was positioned around the endometrium and tracked over time. The strain rate of uterine muscle was then extracted to generate a time-space representation. This was analyzed in the 2D Fourier domain for the assessment of UP (contraction wave) speed and direction, determined by the two dominant spectral peaks.
The ex-vivo results confirmed the accuracy of the implemented adaptive optical flow method for uterine speckle tracking. In vivo, different propagation directions were observed. The estimated UP speed was 0.88 ± 0.28 mm/s (upstream) and 1.27 ± 0.69 mm/s (downstream), which is in line with the literature based on visual inspection [3]. These promising results represent a first step towards a better characterization and understanding of UP. Extended studies with more patients will elucidate on the actual limits of the method, and the role it can play in clinical practice, with emphasis on fertilization procedures.
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14:00
15 mins
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Needle-Hepatic Vessel Interaction Forces: Adding Blood Vessels to a Liver Phantom
Tonke L. de Jong, Sander van der Velden, Jenny Dankelman, John J. van den Dobbelsteen
Abstract: Introduction: Data on needle-tissue interaction in human specimens are scarce. For example, the forces that are involved upon puncturing hepatic vessel walls are unknown. More knowledge about these forces is needed to develop high fidelity liver phantoms, which can be used in testing novel needle designs, validating robotic systems and training of medical residents. Therefore, the goal of the current study is to give insight into the needle tip forces upon insertion through hepatic vascular walls, and to provide a phantom material that mimics these forces.
Methods: Small pieces of liver tissue and blood vessels, i.e. arteries, portal veins and hepatic veins, were extracted from three fresh-frozen human cadavers. In addition, four different specimens of silicone (Smooth-Sil 950) were fabricated, ranging from 0.6-1.2mm thickness, with or without a mesh fabric attached, which allows for fastening silicone with other tissue mimicking materials, such as Polyvinyl Alcohol (PVA). An 18 Gauge trocar needle was inserted through the specimens under a constant velocity (5mm/s) by means of a linear stage. Insertion forces were captured, after which the peak forces and force-position profiles were compared among the different tissue and phantom specimens.
Results: A total of 231 needle force measurements were done in liver specimens. Puncturing hepatic veins (median: 2.2N, IQ range: 1.5N – 3.7N, n = 173) resulted in the highest needle forces, followed by hepatic arteries (median: 1.3N, IQ range: 1.2N – 1.8N, n = 11), and surrounding liver tissue (median: 0.4N, IQ range: 0.3N – 0.5N, n = 47). Concerning the silicone vessel specimens without the mesh fabric; a minimum thickness of 0.9 mm was needed to mimic the needle insertion forces. A thickness from 0.6mm was appropriate for the silicone specimens with mesh. Force profiles were comparable.
Conclusion: Needle insertion forces into hepatic vessel walls are higher than insertions into surrounding liver tissue. This study showed that silicone blood vessel specimens with a mesh fabric attached are suitable to mimic these forces. Therefore, they can be added to current state-of-the-art liver phantoms. Furthermore, the needle force data collected in this study can have broader applicability, for instance to develop needle path planners and to design novel needles.
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14:15
15 mins
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Enhancing Lateral Contrast and Resolution Using Multi-Perspective Ultrasound Imaging: Applied to Abdominal Aortas
Niels Petterson, Marc van Sambeek, Frans van de Vosse, Richard Lopata
Abstract: Abdominal aortic aneurysms (AAAs), dilations of the abdominal aorta, can rupture and cause a fatal haemorrhage. Treatment is possible, however, not without risk for the patient. Surgery is decided upon when the diameter exceeds a threshold, based on a population average outcome. However, some aneurysms rupture below this threshold, while others remain stable above this criteria. A better rupture risk assessment is needed.
Ultrasound is widely used to examine both geometry and dynamic motion of the aorta. These parameters serve as input for novel computer models which estimate the stress and stiffness of the vascular wall. The stress and stiffness can be used as possible rupture risk markers. The accuracy of the models is greatly dependent on their input. Low lateral contrast and resolution in ultrasound cause large variance in both geometry and motion estimation. Therefore, this study proposes multi-perspective imaging to enhance both contrast and resolution.
2-D cross-sectional ultrasound views of the abdominal aorta were acquired with a curved array probe in 6 healthy volunteers. Images from multiple perspectives were taken by physically moving the probe over the abdomen from side to side. 5 acquisitions were made under angles between -30° and +30°. An arch construction was used to fixate the probe, restricting it to a single plane. To manually segment the spine, its visibility was enhanced by calculating the cross-correlation coefficient of image sectors over an entire heart cycle. The stationary spine will yield high correlations. Segmentations of both the spine and the aorta were used to register the acquisitions. Electrocardiograms were used for time-alignment. Compounding was realized by averaging the envelope intensities.
Compounding showed a significant increase in image clarity, especially of the aortic wall. Contrast-to-noise ratios increased by a factor of 3.2, from 0.074 to 0.240. The contrast increase is present during the entire heart cycle. Slight changes in heart frequency caused only minor temporal misalignment. The enhanced images increase accuracy of vascular geometry and motion detection, and could improve rupture risk assessment in AAAs. Ongoing work focuses on more advanced compounding schemes as well as the combination of motion vectors from multiple perspectives.
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14:30
15 mins
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Quantitative third harmonic generation microscopy for assessment of presence/absence of diffuse glioma in human brain tissue
Zhiqing Zhang, Jan de Munck, Niels Verburg, Annemieke Rozemuller, Willem Vreuls, Laura van Huizen, Sander Idema, Eleonora Aronica, Philip de Witt Hamer, Pieter Wesseling, Marie Louise Groot
Abstract: -
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14:45
15 mins
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Efficacy of MRI in Determining the Effect of Gravitation and the True Extent of Prolapse in the Standing Position.
Anique Grob, Judith olde Heuvel, Jurgen Futterer, Diana Massop, Angelique Veenstra van Nieuwenhoven, Frank Simonis, Huub van der Vaart
Abstract: Objective: Pelvic organ prolapse is clinically diagnosed in supine position, even though complaints mostly occur in upright position. In clinical practice the effect of gravity is usually simulated by having the patients put strain on their pelvic floor by performing a Valsalva manoeuvre, while being in supine position. The objective of this study was to evaluate the efficacy of MRI in determining the effect of gravitation and the true extent of prolapse in the standing position.
Methods: This prospective study was conducted with symptomatic pelvic organ prolapse grade ≥ 2 patients. Fifteen female patients were examined with a tilting Magnetic Resonance Imaging (MRI) system, to allow supine and upright imaging of the pelvic floor. The differences in distances of the bladder neck, cervix and pouch of Douglas to the pubococcygeal line (PCL) between supine and upright, were estimated together with changes in the genital hiatal area. Patients were scanned at rest and during straining. The data was analysed by one observer, with nine year of experience in abdominal radiology. The distances in the different situations were compared using the Wilcoxon ranking test.
Results: Of the 15 datasets, one sagittal MRI dataset was of insufficient image quality and was excluded from analysis. Furthermore, one patient had no uterus, thus the PCL-cervix distance could not be determined. All mean distances to the PCL increased from supine-strain to upright-rest and from supine-strain to upright-strain position. These distances between difference positions changed as: the bladder descended 1.3 cm to 1.4cm; the cervix 1.1 cm to 2.2 cm and the pouch of Douglas 0.8 cm to 1.5 cm, respectively (all p-values < 0.05) (Figure 1). The hiatal area was larger in upright-strain position (mean 42.0 cm2; SD ±14.8) than during supine-strain position (mean 33.5 cm2; SD ±14.5), with a p-value of 0.02.
Conclusion: Upright MRI scanning of patients with POP grade ≥ 2 at rest and during straining shows a significantly larger extent of the prolapse than what is observed during supine straining. In case of discrepancies between symptom severity and the observed prolapse stage, upright staging may be of use to establish the true extent of prolapse.
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