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A training phantom for ultrasound-guided needle insertion and suturing

A training phantom for ultrasound-guided needle insertion and suturing
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  1 Evaluation of an In-House GYN BrachytherapyTraining Phantom K Nattagh, T Siauw, Pouliot J., I-C Hsu, J A M Cunha UC San Francisco, San Francisco, CAAugust 10, 2013  Abstract —PURPOSE: During gynecological (GYN) brachytherapy(BT), suturing of the cervix and image guided needle insertions arehighly skill dependent tasks. Medical residents often have to practicethese techniques in the operating room; this can be sub-optimal forthe patient. We present a fast and low-cost method of building realisticand disposable GYN phantoms which can be used to train physiciansnew to GYN BT.METHODS: Phantoms were comprised of a rectal cavity large enoughto accommodate a standard trans-rectal US probe, a vaginal cavity, auterus, a uterine canal, and a cervix, all embedded in a gelatin matrix.The uterus was made of gelatin and coated with rubber to mimic thetexture of soft tissue and for CT and US image contrast. Phantom’sdurability, longevity, construction times, materials costs, CT and USimage quality were recorded. An attending brachytherapy physicianand 3 medical residents were surveyed on its effectiveness as a trainingmodule.RESULTS: Anatomical structures were distinguishable using CT andUS. For the first phantom, material costs were under $200, curingtime was approximately 48 hours, and active participation time was3 hours. Re-usable parts allowed for reduction in time and cost forsubsequent phantoms: under $20, 24 hours curing time, one houractive participation time. Survey results indicated that the phantomis a useful training instrument.CONCLUSIONS: A method for constructing gelatin GYN phantomswas developed. It can be utilized for training in image guided BTneedle insertion and suturing of the cervix. I. I NTRODUCTION Phantoms are artificial representations of anatomical structures,and they are used in medical research, training, and quality assur-ance. Depending on their use-case, phantoms have different mate-rial, geometric, and technological properties. For example, Rice etal built a 3D head phantom from a material with metabolites thatcould mimic the MRI characteristics of real tissue [1]. Madsen etal designed gelatin phantoms that could be used for heterogeneouselastography because the stiffness of the gelatin could be decreasedin regions where safflower oil is added [2-5]. Kirby et al, studieddeformable image registration using a 2D head and neck phantomconstructed from polyurethane [6]. To study transperineal needleinsertion, Hungr et al designed phantoms that consisted of a rectumand a prostate suspended in a clear and puncturable PVC mixture[7].Although there are phantoms for many different anatomicalregions, an intensive literature search revealed no discussion of construction of an in-house GYN phantom (i.e. vaginal cavity,cervix, uterus, rectum). Specifically, there are no GYN phantomsthat can be constructed in a medical or research laboratory withreadily available materials, quickly and cheaply enough for themto be considered disposable. At the clinic, a phantom of this naturewould be useful for training medical residents in GYN brachyther-apy, which requires suturing and the image guided insertion of needles into the cervix. Therefore, the purpose of this study is todesign and evaluate a GYN gelatin phantom to be used for GYNbrachytherapy training. For this use-case, it should be transparent Fig. 1. GYN gelatin phantom. This GYN phantom was designed to be used asa training tool for medical residents in GYN brachytehrapy. Its puncutrable cervixmimics the texture of soft tissue and thus enables its use in transrectal US imageguided needle insertion and suturing of the cervix. We performed an evaluation of thephantoms longevity, durability, and compatibility with various imaging modalities.A U.S. penny is also shown for scale to allow external visualization of the suturing process, it shouldlook realistic under CT and ultrasound imaging, it should haverealistic tactile and material properties, and it should be resistantto both usage and storage in addition to the aforementioned usefulphantom qualities. Although we have designed this GYN phantomtowards this specific use-case, we believe it will be useful for otherGYN research and medical applications. Figure 1 shows the GYNphantom with the relevant parts labeled.This phantom is specialized for training in GYN brachtherapyprocedures such as the transrectal US image guided insertion of needles and suturing of the cervix. Before treating patients in theOR, medical residents learn these procedures by observing seniorphysicians. This poses two problems: 1) they must observe surgerywithin a very limited field of view 2) both procedures require asignificant amount of experience.For other use-cases, there are GYN phantoms available. Almeidaet al. presented a design and study of a water filled GYN phantomthat could be used in testing treatment planning systems andapplicators, dosimetry, and quality assurance [8]. This phantomwas designed to hold low dose rate BT applicators in a waterfilled housing. It was anatomically correct so that phantom imagingand reconstruction techniques could be more realistically simu-lated. Nazarnejad et al. constructed a GYN phantom for insertingthe GYN applicator that is capable of film dosimetry [9]. Filmdosimetry was achieved in this phantom because it was composedof soft tissue mimicking, Plexiglass slabs which allows it to performdosimetry for different source points.Also, there are GYN phantoms available commercially. Simu-laids Co. produces life-like phantoms that are tailored to train theuser in diagnostic gynecological procedures through anatomical  2 instruction, abdominal palpation, and speculum instruction [10].GYN training phantoms with US compatibility are developed atBlue Phantom Co [11]. They provide users with strong US contrastof anatomical structures so it can be used in transvaginal ultrasoundtraining. These are also highly life-like phantoms and are designedspecifically for obstetrics and ultrasound imaging procedures. Manyof these commercial phantoms cost several thousand dollars.We wanted to create a GYN phantom for our training purposes.One that we could reproduce quickly and economically. It hadto have all the relevant anatomical structures in their respectivepositions (uterus, cervix, vaginal cavity, uterine canal, and rectum).We also wanted it to mimic the texture of soft tissue so we made allstructures with gelatin. The gelatin uterus was coated with rubberto simulate skin.II. M ETHOD AND  M ATERIALS The following sections describe the materials and equipmentrequired to build the phantom, the phantom construction processitself, and our evaluation process for the phantom.  A. Phantom Construction A completed phantom consists of a gelatin matrix, which fillsan acrylic enclosure with two open faces: the ”front”, which iswhere the vaginal and rectal cavities open towards, and the ”top”,which is where the gelatin is poured from. The vaginal and rectalcavities are simulated by cylindrical shafts that run from the frontface to the opposite end of the enclosure. The inside-facing end of the vaginal cavity runs flush to the uterus, which is simulated by apear-shaped gelatin mass. The gelatin uterus is covered by rubbercoating to simulate the skin. The following lists the materials andequiptment used to construct the phantom. Materials: 2x acrylic sheet (20.3cm x 12.7cm x 0.6 cm)acrylic sheet (10.8cm x 21.0cm x 0.6 cm)acrylic sheet (10.8cm x 12.7cm x 0.6 cm)acrylic sheet (13cm x 15cm x 0.3 cm)cylinder (13mm dia x 18 cm)cylinder (6mm dia x 15 cm)cylinder (44mm dia x 13cm)SCIGRIP 16 fast set acrylic bonding agentPerformix Co. Plasi-dip liquid rubber coatingIndustrial grade porcine gelatinclayplastic wrapwater (2.0L)70% ethanol solution Equipment: drillrefrigeratorelectric stove or similar heating sourceC-clamps (size/s)computer-aided design (CAD) software *3D printer 1 *stirring spatula2L potthermometer 1 There are many online services available for this.Fig. 2. An illustration of the computer aided designing technique used to create theuterus and vaginal cavity. (a) A virtual, hollow cylinder and a virtual uterus weredesigned. (b) These were made to overlap such that the uterus had an anatomicallycorrect depth and angle with respect to the vaginal cylinder. Once they overlapped,a common CAD technique called ”subtraction” was carried out. Here the uterus,and any volume it was overlapping with, disappears. (c) After the subtraction wascarried out. Now, if this new vaginal cylinder and the old uterus is printed, theywill have matching geometries. * optionalThe phantom construction procedure consisted of (1) vaginalcavity and uterus preparation, (2) housing assembly, (3) gelatinpreparation, and (4) phantom assembly. These steps are describedin detail in the following paragraphs.The vaginal cavity starts as a positive mold. Later, the vaginalcavity positive was removed from the phantom to produce thevaginal cavity. The uterus starts as a negative mold which will laterbe filled with gelatin to make the uterus positive. Since the vaginalcavity and uterus must be flush together, their geometries weredesigned together using computer-aided design (CAD) software.The size and shape of the uterus and vaginal cavity dimensionswere specified by a brachytherapist to simulate a typical anatomicalcase. Specifically, the vaginal cavity positive was designed as a 4.4cm diameter by 13 cm length cylinder (the vaginal cavity itself does not have to be this long, later steps will show that 13 cm isan upper bound and the length of the vaginal cavity is adjustable).The uterus was designed as a pear-shape: 8.2 cm long, 4.8 cm wideat its widest section, and 2.6 cm wide near the cervix. In the CADsoftware, the uterus was placed in an anti-verted position relativeto the vaginal cylinder, its correct anatomical configuration, and theintersection volume was subtracted from the vaginal cylinder. Thisprocess is shown in Figure 2.Once the vaginal positive and the uterus negative were designed,they were exported to Standard Tesselation Language (STL) filesand 3D printed using a Z-Printer 150 3D printer. After printing,both parts were placed in an 8 ◦ C refrigerator to expedite later stepsin the construction process. 3D printing services which allow forsubmission of designs and will ship the finished product (with aturnaround of a few days) are available online [12-14]. So, directaccess to a 3D printer is not necessary for constructing thesephantoms. Also, these parts only need to be created once and canbe re-used for subsequent phantoms (unless several phantoms areto be made once). The STL files used for this project are availablefor download if request is made via email.We then used the uterus mold to make the gelatin uterus (Figure3). We prepared a gelatin mixture to fill the uterus volume. Forevery 100 mL of room temperature water, 12g of gelatin powderwas gradually stirred into the water. The mixture was heated to50 ◦ C over 10 minutes with constant stirring.Before the gelatin mixture was poured through the hole of theuterus mold, C-clamps were used to secure the two halves of theuterus mold together. After pouring the gelatin into the mold, the6mm (diameter) rod was passed through the hole so that it couldact as a positive for the uterine canal (note that smaller diameters  3 Fig. 3. A series of images depicting how the rubber coated gelatin uterus wasconstructed. (a) The 3D printed uterus negative and vagina positive. (b) The 3Dprinted parts after the uterus mold was used to make the gelatin uterus.(c) The rodused to make the uterine canal being used to dip the gelatin uterus into liquid rubber.(d) After the liquid rubber cured on the surface, the rod was removed and the rubbercoated gelatin uterus was complete. can be used if preferred). The set up was allowed to sit for 30minutes so that the c-clamps were no longer necessary, it was thenplaced in the refrigerator to expedite the solidifying process. Afterfour hours, the gelatin uterus was removed from the mold (with therod still in place).Once the gelatin uterus was removed, the rod was used as ahandle to submerge the uterus in liquid rubber to give it an outer-skin that would provide US and CT contrast. The uterus wasallowed to hang for one hour before being placed in a refrigeratorto expedite the solidifying process (note that more layers of rubbercan be used to make the cervical surface tougher).Next, the phantom housing was constructed. The phantom hous-ing was constructed from five acrylic sheets. Each side is labeledin Figure 4. Sides 1-4 were sealed together using acrylic bondingagent. Side 5 was designed as a removable wall. Before securingside 5 to the others, two circular holes were drilled into it withdiameters 4.4 cm, and 1.3 cm, respectively, to allow passage of the vaginal cylinder positive and 1.3 cm rod, respectively. Bothholes were centered along the bottom edge of the removable wall;the centers of the 1.3 cm and 4.4cm hole were located 3.5 cmand 8 cm from the bottom edge, respectively. The vaginal cylinderand the 1.3 cm diameter cylinder were then passed through theirrespective holes in Side 5. The edges between the cylinder andthe removable wall were sealed with clay. The seal should be aswater tight as possible. Similarly, the vaginal cylinder was attached.The removable wall was then held against the foundation with theC-clamps and its edges were then sealed with clay. An image of the set up is illustrated in Figure 5. The cylinders were manuallysupported in position until the gelatin was poured and they couldthen be supported from the buoyancy of the gelatin. The uterus wasthen inserted into the vaginal cylinder in an antiverted fashion. Thefit should be tight enough such that the uterus can stay in place. Fig. 4. Four acrylic sheets (labeled 1, 2, 3, and 4) were sealed, with acrylic bondingagent, to make the housing that will encase the gelatin phantom. Acrylic sheet (5)had two holes drilled into it. The positive molds for the rectal and vaginal cavitieswill be passed through the holes and the sheet will then be secured against thehousing.Fig. 5. The set-up before liquid gelatin was poured into the phantom housing.Junctions between the 5th acrylic sheet and the: vagina positive, rectum positive,and the phantom housing have been sealed with clay. C-clamps are used to furtherprevent leaks. The uterus fit into to the posterior hole of the vaginal cylinder as thedesign intended, in an anti-verted position. Two liters of gelatin mixture was then prepared with the sameproportions as for the uterus. The mixture was poured into thephantom housing until the uterus was completely submerged. Thephantom was left at room temperature for four hours beforethe clamps were removed and the phantom was placed in therefrigerator.After solidifying in the refrigerator, Side 5 was removed, fol-lowed by the two cylinders. To remove the cylinders, they weregyrated repeatedly (note that it was helpful to place a few dropsof water in between the cylinders and the gelatin when removingthem to diminish adhesion between the cylinders and the gelatinmatrix). This is when the phantom construction was complete andthe phantom looked like Figure 1.  4  B. Phantom Evaluation This section describes our physical, imaging, and pedagogicalevaluation of the GYN phantom.We scanned the phantom using a Siemens spiral CT (120 kV)and using a Phillips transrectal ultrasound probe. A qualitativeassessment was made of the contrast between the uterus and uterinecanal and the uterus and gelatin matrix.We determined the longevity of the phantom by storing it in therefrigerator until it was unusable, which we defined as 2mm of gelatin liquefaction on any of the phantom surfaces. The phantomwas checked daily for this condition.To offset dessication and bacterial degradation of the gelatin,we stored the phantom in a particular way. When the phantom wasready to be stored, we spraying the two cylinders with 70% ethanoland, after they dried, placed them back into their correspondingcavities. We then wrapped the phantom with seran wrap and placedit in a 8 ◦ C refrigerator.To increase longevity, we conducted a parallel study with 2mgof thimerosal (antiseptic/antifungal agent) added for every 1 mLof liquid gelatin. Note that thimerosal is rated as a level 3 healthhazard according to NFPA704, but may be worthwhile if longevityis important.The durability of the rectal wall was evaluated by insertingand removing a transrectal ultrasound probe 50 times. Aquasonicultrasound lube was used. A qualitative assessment of the damageto rectal wall was made by checking for fissures and changes inthe texture of the gelatin.The durability of the cervix was evaluated by puncturing it 20times with suturing needles. A qualitative assessment was made bychecking for any type of change in texture when punctured.The phantom used by an attending brachytherapy physicianand co-author, IH, to demonstrate suturing of the cervix andbrachytherapy needle insertion to three medical residents.Afterwards, they were surveyed to evaluate the effectivenessof the phantom as a training module. Below are the survey question: Survey: 1) The texture of the phantoms cervix resembled the realcase during suturing.2) Guidance and positioning of catheters in the phantomresembled the real case.3) US image guidance in the phantom was similar to reallife.4) The phantom improved your skills in both procedures.5) You are more comfortable performing both proceduresafter using the phantom.A rating of 1 on a scale of 1  −  5 was a strong affirmation.III. R ESULTS The uterus negative and vagina positive were designed in approx-imately two hours and 3D printing took five hours. The phantomhousing took under 10 minutes to construct and 3 hours to cure.The preparation of the gelatin uterus took 0.25 hours of activeparticipation time, it took 10 hours total when the curing timesassociated with the gelatin and the rubber are included. The curingthe gelatin matrix that filled the phantom housing took 14 hourswith 0.5 hours active participation time. In summary, constructionof first phantom from scratch took approximately three hours of active participation time and two days including all the curing times.As the phantom foundation, uterus negative, and vaginal cylinder Fig. 6. CT images of the phantom. (a) Axial cross section shows contrast betweenthe cervix and the uterine canal. (b) Sagittal cross section shows contrast betweenthe uterus and the surrounding matrix.Fig. 7. (a) An attending brachytherapy physician using a transrectal US probe tohelp guide a BT needle into the uterus. (b) Axial cross section of uterus taken witha transrectal US probe. The BT needles needles show up as bright spots on the US.The uterine wall is also distinguishable. can be reused, the time of assembly of the following phantomswas primarily constrained by the curing time of the gelatin matrix.Therefore, following phantoms were constructed in about one hourof active participation time and 24 hours of curing time.The materials cost for the 3D printing was under $200. This wasthe significant component of the total cost. Since the 3D printedparts and phantom housing are reused, material costs for subsequentphantoms was reduced to under $20.The average survey results were 1 for all statements. So far wehave received a one for all survey questions. However, these resultsare from in-house physicians and we only tested this on four sofar.Figure 6 shows a CT image of the phantom. Figure 6a showscontrast between the cervix and the uterine canal. The contrastbetween the uterus and the surrounding matrix is depicted in figure6b. In figure 7a, a transrectal-US probe is being used to help guidea BT needle into the uterus. The BT needles are represented by thebright spots in Figure 7b. Figure 8 shows a suturing needle seenthrough the gelatin matrix.The phantom lasted two weeks in refrigerated 8 ◦ C storage. Theaddition of thimerosal extended the lifetime to 6 weeks. After 50probings of the rectal wall, no sign of degradation was observed.After 20 insertions on the suturing needle there was a slightsoftening in texture of the phantom cervix.  5 Fig. 8. A suturing needle seen through the wall of the phantom. As one of themain issues in GYN BT training is how hard it is to observe the procedures,the transparency in the gelatin may be a useful characteristic. Here, the attendingbrachytherapy physician is about to show a medical resident how suturing isperformed on the cervix. IV. D ISCUSSION This phantom can be built without CAD software and a 3Dprinter. The vaginal cylinder and the uterus can be made with mosttypes of sturdy pottery clay and traditional molding techniques.If you do not want to mold or CAD yourself, the STL files areavailable on email request. You can also use on-line services tohave the parts printed and sent to you. Some examples are [12-14].Future endeavors include using phantoms for preliminary studieson new image guided treatments and preparing the phantom formulti modality treatment planning. Experiments will include quan-titatively determining material properties and adjusting accordinglyto achieve optimal contrast in CT and/or US imaging. Such proper-ties include acoustic and x-ray attenuation coefficients, propagationspeeds, and backscatter.V. C ONCLUSION A method and recipe for constructing GYN phantoms wasproduced. These phantoms consist of a vaginal cavity, rectal cavity,and gelatin uterus; all suspended in a gelatin matrix. They can bemade quickly, with low cost, and with basic laboratory equiptment.CT and transrectal US images show a strong contrast betweenthe anatomical structures. Medical residents confirmed that theprocedures with the phantom were realistic, the phantom helpedincrease their skills in GYN BT, and that they felt more comfortablein the OR after using the phantom.VI. A CKNOWLEDGEMENTS We thank all the physicians that used the phantom and providedus with feedback. We also thank the Conolly Lab at UC Berkeleyfor generously lending us the use of their 3D printer for this project.R EFERENCES[1] J. R. Rice, R. H. Milbrandt, E. L. Madsen, G. R. Frank, E. J. Boote, and J. C.Blechinger  Anthropomorphic 1H MRS head phantom.  Med Phys. 1998 Jul;25(7Pt 1):1145-56.[2] Madsen EL, Hobson MA, Frank GR, Shi H, Jiang J, Hall T, Varghese T, DoyleyMM, Weaver JB.  Anthropomorphic Breast Phantoms for Testing ElastographySystems  Ultrasound in Medicine and Biology. 2006a;32(6):857874.[3] Madsen EL, Frank GR, Hobson MA, Shi H, Jiang J, Varghese T, Hall T. Spherical lesion phantoms for testing the performance of elastography systems Physics in Medicine and Biology. 2005a;50:59835995.[4] Madsen EL, Hobson MA, Shi H, Varghese T, Frank GR.  Stability of het-erogeneous elastography phantoms made from oil dispersion in aqueous gels Ultrasound in Medicine and Biology. 2006b;32(2):261270.[5] Madsen EL, Hobson MA, Shi H, Varghese T, Frank GR.  Tissue-mimickingagar/gelatin materials for use in heterogeneous elastography phantoms  Physicsin Medicine and Biology. 2005b;50:55975618.[6] N. Kirby, C. Chuang, and J. Pouliot,  A two-dimensional deformable phantom for quantitatively verifying deformation algorithms  Med. Phys. 38(8), 4583(2011).[7] N. Hungr, J.-A. Long, V. Beix, and J. Troccaz1  A realistic deformable prostate phantom for multimodal imaging and needle-insertion procedures  Med. Phys.39, 2031 (2012)[8] C. E. Almeida, M. Rodriguez, E. Vianello, I. H. Ferreira, and C. Sibata  An an-thropomorphic phantom for quality assurance and training in gynaecologicalbrachytherapy  Radiotherapy and Oncology 63 (2002) 75-81[9] M. Nazarnejad, S. R. Mahdavi, K. Asnaashari, M. Sadeghi, and A. Nikoo-far  Developing a Verification and Training Phantom for Gynecological Brachytherapy System  Iranian Journal of Medical Physics, Vol. 8, No. 1, Winter2012, 33-40[10]  Simulaids - EVA Gynecologic Manikin  N.p., n.d. Web. Accessed 08 June 2013[11]  Blue Phantom Endovaginal Ultrasound Training Models.  N.p., n.d. Web.Accessed 08 June 2013[12]  ColorJet Printing (CJP - ZPrint) — Rapid Prototyping — N.p., n.d. Web. 09 July 2013 [13]  Grow It — Rapid Prototyping & Manufacturing. GROWit 3D Printing. N.p.,n.d. Web. 09 July 2013. [14]  ”Rapid Prototyping.” Solid Concepts Inc. N.p., n.d. Web. 09 July 2013.
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