problems & solutions in fibroid ablation with mrghifus

Problems & Solutions in Fibroid Ablation with MRGHIFUS

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Problems & Solutions in Fibroid Ablation with MRGHIFUS

Award: AOSR Best Exhibit Prize - Bronze

Poster No.: R-0220

Congress: RANZCR-AOCR 2012

Type: Educational Exhibit

Authors: B. Raghavan, M. Logudas, R. Balaji, R. Arafat, A. Wasim

Keywords: Interventional non-vascular, Genital / Reproductive system female,MR, Ablation procedures, Economics

DOI: 10.1594/ranzcraocr2012/R-0220

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Learning Objectives

Magnetic Resonance - High Intensity Focused Ultrasound is a relatively new non-invasive, out-patient procedure which ablates only the fibroid. However in order to getoptimum results it is necessary to titrate the procedure for each patient so that thetechnique benefits the patient.

Conventionally uterine fibroids have been treated surgically by myomectomy,hysterectomy (1) and medically with hormones and uterine artery embolisation. Mostwomen in the younger age group like to conserve their uterus; however recurrenceis a problem in all these therapies. Myomectomy and hysterectomy have the riskof anesthetic and post surgical problems like scarring and adhesions besides theroutine admission post-op care and post-op recovery time (1-2 weeks) needed for anabdominal surgical procedure. Uterine artery embolisation (2) is minimally invasivebut ovarian artery ablation can be a problem besides complications of cathetertechniques.

This exhibit is a pictorial essay is to illustrate various problems that can beencountered during Magnetic Resonance Imaging-guided High Intensity FocusedUltrasound (MR-HIFU) therapy for uterine fibroids based on our initial experience.Whilst some modifications are on the technical aspect, there are several modificationsduring therapy which make the fibroid accessible and amenable for ablation

Background

The basic principle of MRHIFU is thermotherapy with focused ultrasound wavesunder MR guidance(3) where the MRI acts as a thermometer and monitors themorphological changes by real time acquisition.

A focusing transducer is used to bundle ultrasound energy into a small volume atthe target locations inside the body. During treatment, the ultrasound energy beampenetrates through the skin and soft tissue causing localized high temperatures onlyin the focus area producing coagulative necrosis, leaving the skin and intermediatetissue and tissue posterior to the fibroid unharmed

Magnetic Resonance Imaging is the only modality able to measure temperaturechanges within the human body non-invasively. This, combined with its excellentsoft tissue contrast and 3D imaging capabilities, makes MRI a preferred method for

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planning and monitoring non-invasive thermal ablation processes such as HIFU.3Danatomical images provide the reference data for treatment planning, while real-time temperature sensitive images follow the ablation process to provide informationabout treatment progress and monitor critical anatomical structures.

Volumetric ablation technique (4) is the sonication method used in ablation. In thistechnique the focal spot can be steered in concentric circles of increasing diameterand hence treatment cells of varying sizes from 4mm to 16 mm can be used. Thisis expected to result in better energy efficiency as the inherent outward diffusion ofheat from the inner circle is utilized to preheat the outer circle instead of allowing itto dissipate. The increased energy efficiency can result in shorter treatment time,enabling larger treatment volumes. [Fig 1].

Images for this section:

Fig. 1: Volumetric ablation

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Imaging Findings OR Procedure Details

Procedure Details:

All our cases have been treated on using the 1.5 Tesla MR unit with the pelvic coilwith the add-on compatible HIFU table.

Case selection :

Pre-procedural counseling and screening MRI in the prone position has a vital rolein patient selection.

Counseling and co-relating the patient's complaints and symptoms and signs will helpin deciding if the patient will benefit from therapy.

The common presenting symptoms are due to:

Bleeding problems:

• Very heavy and/or prolonged menstrual flow, can lead to anemia• Irregular blood loss between menstrual periods

Pain symptoms:

• Abdominal and pelvic pain, back pain, pain in legs• Pain during sexual intercourse

Bulk-related symptoms

• Pelvic pressure or heaviness• Frequent urination due to bladder pressure• Constipation an bloating due to pressure on the bowel• Abnormally enlarged abdomen

Reproductive problems

• Infertility• Multiple miscarriages• Premature labor

The data includes a total of 67 patients who were assessed for suitability for thisprocedure. The age group ranged from 21 to 63 years, and the maximum number of

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patients had a fibroid volume of 5-10 cms. Most of them were between 40-50 yearsof age.

Out of 67, 33 (49 %) were ineligible, the rest 35 (51%) were eligible, out of this only18 patients opted for treatment, the rest 18 (26 %) did not opt for it even thoughfinancial support was offered (5).[Fig 2]. The various causes for non-eligiblity is non-accessiblity due to bowel loops, followed by Type 3 fibroids & scar due to LSCS .[Fig 3]

Fourteen patients were treated out of sixty-seven patients who have been screenedfor the procedure and one of them had 2 fibroids and was treated in two separatesessions as they were large fibroids. Patients with more than six uterine fibroids ofmore than 4 cm in size are excluded. We were unable to treat three patients, two hadhad severe back pain in the initial few sonications itself and we had to stop therapy.One patient we could not reach the posterior part despite manipulations.

Most of the patients who were treated were symptomatic, [Fig 4]. but we had twopatients who were asymptomatic , the fibroid was detected during the investigationfor infertility. Patients who had large fibroid size were advised that complete ablationwould not happen in one sitting and these patients opted for this therapy over surgeryfor relief of their symptoms (2).

Patients who were desirous of future pregnancy (5) were treated only if they wereinsistent on a non-surgical option after consultation with their gynaecologist.Howeverpatients anxious to conceive needed to be counseled that mere treatment of thefibroid need not necessarily solve their infertility problems Informed consent was takenfor all the patients undergoing treatment after explaining and documenting potentialcomplications and the chances of recurrence and retreatment.

MRI screening is performed on the Achieva or HIFU table after emptying the urinarybladder in the prone position. The following sequences are used -

sag 3d t2 tr 1425 te 130 matrix 512 x 512

t2 tse - tra tr 3659 te 100 matrix 512 x 512 slice thickness mm.

t1 for bowel tr 3.7 te 1.9 matrix 400 x 400

scar sequence tr 21 te6 matrix 400 x 400

thrive tr 5.7 te 2.8 matrix 512 x 512

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temperature mapping using epi technique, tr 36 te 18

angio using ffe technique tr 6.7 te 3.4 matrix 640 x 640

If the fibroid was accessible and suitable for therapy, multiphasic contrast gradientimaging (THRIVE). (Gadolinium injection, 10ml of 0.1mmol/kg) was done. There hasto be at least a gap of 24 hours between administration of Gadolinium and therapy asheat can release the free gadolinium from the injected chelate.

CASE SELECTION

After screening MRI, the fibroid is assessed for the following parameters for itsaccessibility (6) and suitability for therapy (7)

Criteria for eligibility include.

1. Fibroid characteristics:

a. Size

The fibroid volume has to be assessed. The optimum size is above about between3-10 cms.Volumetric computation of the fibroid before and after treatment and non-perfused volume is done by by the sum of slice method from the ROIs in thecontiguous images. This being a volumetric ablation technique larger volumes offibroid can be treated but MR-HIFU device accessibility to fibroids should be such thatat least 50% of the total fibroid volume can be treated. [ Fig.5 & 6].Sonication cannotoccur through a treated area hence the posterior area has to be treated before theanerior area. Fibroids over 10cms can be treated by treating the upper & lower halfin two separate sessions to avoid sonication through the treated area after 1 week.Pre-treatment with GnRH agonist can also be used to shrink the fibroid and improvetreatment outcomes (8).

b. Location

The focal point of the transducer in the earlier version was 8cms in the later versionthis was increased to 10 cms and the centre of the fibroid should be within this. Themeasurement of the focal point fibroid from the skin has to be done giving allowancefor the gel pad (1cms).The serosal margin should come well within the safety margin.Cervical fibroids and fibroids touching the spine or the plexus extending to the spinecan be problematic .Cerevical fibroids [Fig 7] are difficult to manipulate.

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c. Signal Intensities

The MRI signal intensity of the fibroid in T2 is compared to that of the anteriorabdominal muscle and fibroids are classified into 3 types and this is best assessedin the sagittal plane. [Fig. 8]. Degenerating fibroids and those which are calcified arealso unsuitable for treatment. T1 sequences and Ultrasound evaluation are essentialfor these lesions.[Fig 9].

d. Contrast enhancement

Fibroids which enhance with contrast are only suitable as only then the post therapyNPV can be compared with the pre therapy fibroid volume. Also delineation of thevessels can help in targeted vessel ablation during MR-HIFU (9) .Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) helps in the prediction of theimmediate therapeutic response of MR-guided high-intensity focused ultrasound(HIFU) therapy in the treatment of symptomatic uterine fibroids (10).[Fig 10].

2. Scar

Post LSCS or abdominal surgical scars can come in the way of the Ultrasound beampath resulting in heating of the scar at the superficial level. So the Scar sequenceis done to map out the scar and clips. The lower uterine segment horizontal scar ofLSCS if thin and old and we may be able to sonicate through the scar. In our Systemthe Ultrasound elements can be selectively switched off in the region of the scar. Thescar in the MRI image is mapped out and the data fed into the HIFU therapy consoleand the appropriate elements are switched off. But it is essential to calculate the ATVvirtually so that we can predict if we are able to treat sufficient volume (50% of thefibroid) after switching off the relevant elements. [Fig 11,12]

3. Bowel loops and Bone

Cases where the small bowel loops or any other structure anterior to the fibroid whichcome in the path of the ultrasound beam are unsuitable for this procedure. But smallbowel loops can be pushed up and careful monitoring during sonication with the bowelsequence is useful. [Fig 13]

Proximity to the pubic bone and spine can cause heating and pain (11). Low energiesare sufficient to heat a bone surface to high temperatures as bone absorbs ultrasoundwaves more readily than soft tissue. Consequently, nerves lying adjacent to a heatedbone surface may be heated resulting in pain and, in extreme cases, even result innerve damage. Stimulation of the adjacent sacral nerves may cause in severe painresulting in incomplete treatment with reduced efficacy of the procedure. (Fig 14)

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During Therapy

Positioning

The bulk of the fibroid needs to be in the focal zone and positioning have to be doneto ensure the same. Filling up of the bladder with a 3 - way which is connected tothe uro-bag and saline can help in keeping the urinary bladder filled to the requiredlevel. Markers can indicate the original position of the fibroid and ensure that there isno change especially in cases requiring the bladder to be filled to a particular level.Similarly filling up the rectum with ultrasound gel (250-300ml ) to mobilize the smallbowel loops may need to be done.

[Fig 15 & 16]

Cell selection and Heat monitoring:

Cell selection needs to be proper with regard to size and location for optimal treatment.

This technology being a volumetric heating the larger cells are usually found to beeffective i.e 8mm and larger cells (12 ). Though Volumetric ablation technique istheoretically has better energy efficiency it should be noted that this improvementmight not be as large as that of the energy efficiency due to the need for increasedcooling durations The increase in energy absorbed in the near #eld, thus increasesthe near-#eld heating. In order to prevent complications related to excessive near-#eld heating thermal damage to intervening tissue, such as skin burns, longer coolingtimes are mandatory for the larger treatment cells and this results in increased timefor the therapy.

In younger woman it is essential to locate the ovaries and ensure that they will not bewithin the ablation zone.[ Fig 16 & 17]

Also, whilst the larger cells give a larger volume of heat to the fibroid the near and farfield heat safety issues can cause problems and the patient may abort the procedurefor that cell resulting in incomplete sonication. So proper sedation, analgesics beforeand during therapy is mandatory. Also careful monitoring of real time thermal mapand is mandatory. And allowing for adequate cooling time is needed.[ Fig 17]

In order to minimize the amount of heating of bone, sonications can be performedavoiding bony structures. Techniques such as tilting the beam path to avoid bone(Fig 18), increasing the frequency of the ultrasound beam, rectal filling to push thefibroid away from the bone or partial treatment to change the subsequent location /orientation of the fibroid can be done.

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Cumulative dose contours for each cluster plays an important role in assessing theefficacy of sonication as these maps are based on the actual temperatures reached.[Fig 19]

Follow-up

Post ablation Imaging with contrast enhancement demonstrates the Non-perfusedvolume (NPV).

[Fig 19].The NPV guides us regarding further management. If there is a good NPV theprognosis is good. More than 50% NPV is indicative of satisfactory ablation.HigherNPV (>75 %) was predominantly seen in Type 1 fibroids ,where accessibility was nota problem.NPV of 50-75% was seen in whiter and larger type II fibroids. These fibroidshad a mixed response but all patients were symptomatically better.Patients with lessthan 50 % ablation for the treated did not improve (2 patients) and were asked to goin for alternate therapy.

However there can be an over-estimation of non-perfused area in the immediate postablation scan by the edematous myometrium which can revascularise. So all patientsare asked to come for follow-up after 1,3 and 6 months and the size is evaluated byultrasound.[Fig 20]and compared to the pre-therapy size.Contrast MR imaging of thefibroid is performed after after 6 months to assess response.

Risks and complications of MR-HIFU are relatively low and include:

• Possible skin burns.• Pain and/or swelling in the treated area.• Back or leg pain.• Nerve damage.• Nausea.• Abdominal cramping.• Fever.• Vaginal discharge.• Urinary tract infection.• Bowel perforation.

The complications [ Fig 21] that occurred in our study were transient and managedsymptomatically. Three patients who had vaginal discharge had submucosal fibroids.Patients with larger fibroids with longer treatment times complained of back andleg pain during sonication of the posterior part of the fibroid that was managed byanalgesics.

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Images for this section:

Fig. 2: Distribution of screened patients according to eligiblity for MR-HIFU.

Fig. 3: Causes for in-eligiblity.

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Fig. 4: Symptoms of treated Patients.

Fig. 5: The empty bladder was covering the fibroid and coming in the sonication path (1stimage in the left ), the bladder was filled ( middle image), however this pushed the fibroidposteriorly and filling the rectum with gel (third image to the right )did not help either asonly 1/3 of the volume was available for treatment and despite manipulation this patientwith a fibroid volume of 530 ml could not be treated.

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Fig. 6: This larger volume of Type 2 fibroid of 664 ml was accessable & could be treatedfor a total of about 175 minutes in a single session resulting in a post ablation Nonperfused volume (NPV) of 57%. nOTE,the non-perfused area appears to extend to the

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serosa at L4-L5 level(red arrow in the sagittal image), was due to the edema secondaryto increased heating where the bone touched the fibroid,which subsequently resolved.

Fig. 7: Cervical (Type 1)fibroid in the first image was deep (>10cms ) and could not bepushed anteriorly by rectal filling. The middle & 3rd image are pre & post rectal filling of apatient with a deep predominently Type 1 fibroid in the posterior aspect of the the uterinebody leading to a position suitable for satisfactory ablation.

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Fig. 8: One of our patients had huge fundal Type 3 fibroid but she had additional type1 fibroids which was distorting the cavity and causing severe menorrhagia. She wasreferred for treatment of these fibroids as she did not want surgery and the gynecologistfelt that ablation of these could give her symptomatic relief.

Fig. 9: 25 year old lady 3 months after abortion came with a fibroid.Red degeneration inthe fibroid which appeared hypointense on T2 (left) and hyperintense on T1(right).

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Fig. 10: This patient had two type 2 fibroids but with differing signal intensities the lateralfibroid did not enhance with contrast and portion of the portion of this lateral fibroid whichwas treated (indicated by yellow cells)shows poor response in the post ablation scan.

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Fig. 11: This patient has previous LSCS scar the vertical scar is thin and is seen in themidline in the scar sequence (red arrow ) overlying a Type 1 an otherwise accessiblefibroid.

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Fig. 12: Therapy is simulated on the HIFU console with the screening images and weare able get an idea of the available treatment area (ATA) when the ultrasound elementsoverlying the scar are switched off.

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Fig. 13: Bowel loops completely cover the fibroid in the two series of images (upper &lower) and can be difficult to displace and the proximity to the pubic bone can causeheating of the bone. Additionally a cystic ovary is seen in the path of sonication in thelower series.

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Fig. 14: Heating is seen in the far-field in the region of the plexus causing the patient toabort the sonication and terminate therapy in the subsequent sonications.

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Fig. 15: This patient had multiple small fibroids with no overlying bowel loops during initialscreening. However, on the day of therapy bowel loops had moved anterior to the fibroid.The bladder was filled to displace the bowel loops and the position was maintained byplacing markers to indicate the correct position.

Fig. 16: This patient on the screening scan 1st image did not have bowel loops in the pathof sonication. Filling up of the rectum, maneuvering of the loops away from the sonicationpath by mobilizing the patient and pushing the bowel loops away from the fibroid duringpositioning helped.

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Fig. 17: The right ovary indicated by the red arrows is away from the cell safety margin

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Fig. 18: Heating in the far field has to be monitored and during therapy by looking at thereal time temperature maps ( left image ), thermal dose and dose contour of the cell (rightimage red is the thermal dose & white is the dose contour ).

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Fig. 19: This patient had near field heating on the anterior abdominal wall at the site oflaparoscopic sterilization not visible in the screening sequence. The thermal dose mapof the focus is also distorted.

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Fig. 20: In this patient with multiple fibroids the tilting of the transducer away from thepubic bone helped in treating the lower fibroid.

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Fig. 21: Post ablation follow up ultrasound at 3rd month shows reduction in volume.

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Fig. 22: This submucosal fibroid is an ideal fibroid show 90% NPV and the cumulativedose matches cell distribution and fibroid contour (3rd row white outline).

Fig. 23: Incidence of Complications.

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Conclusion

MR-HIFU is a new technique for fibroid ablation which will be compared to laparoscopyand robotic assisted for which proper selection of the patients needs to be done with alarge referral base. Being a non-invasive out-patient procedure, it is more cost-effective(13) and has the potential to be a first line therapy before surgical options. Establishmentof fibroid clinics with good co-operation between the gynaecologist and the radiologistcan help. However awareness of the problems and a learning curve in acquiring theskill for this procedure is needed so that we can overcome the various problems someof which are faced on the therapy table.

Personal Information

Dr.Bagyam Raghavan

Senior Consultant Radiologist,

Apollo Speciality Hospitals,

Chennai.

[email protected]

References

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2. Elizabeth A. Stewart, et al. Sustained Relief of Leiomyoma Symptoms by UsingFocused Ultrasound Surgery.Obstet Gynecol 2007;110:279.

3. Jaron Rabinovici et al Clinical improvement and shrinkage of uterine #broids afterthermal ablation by magnetic resonance-guided focused ultrasound surgery.UltrasoundObstet Gynecol 2007; 30: 771-777.

4.Vooqt m.j et al .volumetric feedback ablation of uterine fibroids using magneticresonance-guided

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high intensity focused ultrasound therapy Eur Radiol. 2012 Feb;22(2):411-7.

5. Jaron Rabinovici et al Pregnancy outcome after magnetic resonance-guided focusedultrasound surgery (MRgFUS) for conservative treatment of uterine #broids..Fertility andSterility 2008 by American Society for Reproductive Medicine

6. Behera M.A. Eligibility and accessibility of magnetic resonance-guided focusedultrasound (mrgfus) for the treatment of uterine leiomyomas.Fertility & Sterility 2010oct;94(5):1864-8.

7. Yoon .S.W et al Patient selection guidelines in MR-guided focused ultrasoundsurgery of uterine fibroids: a pictorial guide to relevant findings in screening pelvicMRI.Eur .Rad.2008 Dec;18(12):2997-3006.

8. Smart OC, Hindley JT, Regan L et al. Gonadotrophin-releasing hormone and magnetic-resonance-guided ultrasound surgery for uterine leiomyomata. Obstet Gynecol 2006;108(1):49-54.

9. Vooqt M.J et al .Targeted vessel ablation for more efficient magnetic resonance-guidedhigh-intensity focused ultrasound ablation of uterine fibroids. Cardiovasc Intervent Radiol.2011 Dec 7.

10. Kim Y.S.E et al.Dynamic contrast-enhanced magnetic resonance imagingpredicts immediate therapeutic response of magnetic resonance-guided high-intensityfocused ultrasound ablation of symptomatic uterine fibroids. Investgative Radiol.2011Oct;46(10):639-47.

11.Hipp.E et al. safety limitations of mr-hifu treatment near interfaces: a phantomvalidation. Journal of applied clinical medical physics, 2012 mar 8;13(2):3739. doi:10.1120/jacmp.v13i2.3739.

12. Young-sun Kim et al. A faster nonsurgical solution -Very large #broid tumors yieldedto a new ablation strategy by et al Am J Obstet Gynecol 2011;205:292.

13. Zowall H et al Cost-effectiveness of magnetic resonance-guided focused ultrasound

surgery for treatment of uterine #broids. BJOG 2008; 115:653-662.

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problems & solutions in fibroid ablation with mrghifus

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