MRI IN SURGERYDR. BURHAN R3 S/CDR. JITENDRA R3 S/C

CONTENT OF SEMINAR

1. BASIC OF MRI2. MRI BREAST3. MRI FISTULOGRAM4. MRI DEFECOGRAPHY5. MRCP6. MRI SOFT TISSUE SARCOMA7. MR ANGIOGRAPHY8. MRI FOR LIVER SOL

BASIC OF MRI

Magnetic Resonance Imaging (MRI) produces images of the body’s internal structures by passing radio waves through a powerful magnetic field

Differing frequencies of radio waves are produced by the different body structures, in return, and these are mapped and converted into digital images by a computer.

MRI is especially good for imaging soft tissues in the body, including the brain, nerves, muscles and organs.

WE ALL ARE MADE UP OF ELEMENTS 102 elements occur naturally on earth.

Human body is built of only 26 elements.

Oxygen, hydrogen, carbon, nitrogen elements constitute 96 % of human body mass.

Let us ignore all elements except Hydrogen.

WHY HYDROGEN? Simplest element with atomic number of 1 and

atomic weight of 1

When in ionic state (H+), it is nothing but a proton.

Proton is not only positively charged, but also has magnetic spin (wobble)!

MRI utilizes this magnetic spin property of protons of hydrogen to elicit images!!

BUT WHY WE CAN’T ACT LIKE MAGNETS?

The protons (i.e. Hydrogen ions) in body are spinning in a hap hazard fashion, and cancel all the magnetism. That is our natural state!

We need to discipline them first,

WE NEED A BIG MAGNET FROM OUTSIDE! Magnetic field strength:

0.3 – 7 T (2500 times more than earth’s magnetic field). Average field strength – 1.5 T

Open magnet – less field strength, less claustrophobic

Closed magnet – more field strength, claustrophobic

PROTON ALIGNMENT

Our body protons (hydrogen) align with this external magnetic field.

Now spinning in line with each other

WHAT IS RADIO FREQUENCY PULSE? Same as Radio waves – high wavelength, low energy

electromagnetic waves Radiofrequency coils

Act as transmitter and receiver Different types of coils

Now short bursts of radio waves are sent from the scanner into our body. The radio waves knock the protons from their position.

When the burst of radio waves stops, the protons realign back into place.

The protons in different tissues of the body realign at different speeds.

Therefore, the signal emitted from different body tissues varies. So, for example, softer tissues can be distinguished from harder tissues on the basis of the signals sent.

These signals are detected by a receiving device in the scanner.

The receiving device transmits the signals to a computer.

The computer creates a picture based on the radio signals emitted from the body.

The MRI scanner is noisy so use of some headphones or earplugs to protect our ears from the noise. Quite often we can listen to the radio through the headphones.

T1 weighted image (also referred to as T1WI or "spin-lattice" relaxation time) is one of the basic pulse sequences in MRI and demonstrates differences in the T1 relaxation times of tissues.

A T1WI relies upon the longitudinal relaxation of a tissue's net magnetisation vector

T2 weighted image (also referred to as T2WI "T2 weighted image") is one of the basic pulse sequences in MRI. The sequence weighting highlights differences in the T2 relaxation time of tissues.

A T2WI relies upon the transverse relaxation (also known as "spin-spin" relaxation) of the net magnetisation vector (NMV).

After an RF excitation pulse, there is relaxation of the spins from the transverse plane toward the main longitudinal magnetic vector (B0). This is T1 weighting.

At the same time, spins are decaying from their aligned precession in the transverse plane. Differences in this decay are captured in T2 weighting.

PRE REQUISITION BEFORE MRI No mobiles, no credit cards, Known potential safety concerns due to large static

magnetic field: Internal cardiac pacemakers Steel cerebral aneurysm clips (ferromagnetic) Life-support equipment with magnetic steel Cochlear implants Stents anywhere in the body

Malfunction: ICDs,, bone growth stimulators ,prosthetic heart valves

Superficial burns (uninsulated wire leads)

NEED sedation: infants, younger , agitated adults (claustrophobia)

Precautions: magnetic plastic cards, watches, hearing aids, magnetic steel objects (LEAVE OUTSIDE)

ADVANTAGES OF MRI

No ionizing radiation & no short/long-term effects demonstrated

Variable thickness, any plane Better contrast resolution & tissue discrimination Various sequences to play with to characterize the

abnormal tissue Many details without I.V contrast

DISADVANTAGES OF MRI

Time consuming Not easily available (long waiting list) No on-call service

Faster Less expensive Less sensitive to patient

movements Easier in

claustrophobics Acute haemorrhage Calcification Bone details Foreign body

No ionising radiation Greater details, hence

more sensitive and more specific

Any plane scanning Contrast less allergic

CT MRI

BREAST MRI

BREAST MRI: CURRENT INDICATIONS

Adjunctive screening in high-risk women

Identify occult tumor in women presenting with axillary metastases

Monitor response to neoadjuvant chemotherapy in women with advanced primary tumors

Pregnancy

Screening women with silicone injections

Evaluation of silicone gel implants for rupture

evaluation of pectoralis muscle invasion in women with large or posteriorly located tumors.

Assessment of recurrent disease

Assessment of residual tumor

Scarred Breast

CONTRA INDICATIONS The usual contraindications to MRI, including the

presence of cardiac pacemakers, cochlear implants, and other metallic objects in the body.

Women who are unable to lie prone to be positioned within the breast coil

Women with very large body habitus who cannot fit into the bore of the magnet

Women whose breasts cannot be accommodated within the breast coil

Women with extreme claustrophobia.

TIMING OF MRI BREAST The water content of breast tissue is influenced by the

menstrual cycle and by hormones.

Because both diffuse and focal enhancement may occur in the fourth and first weeks of the menstrual cycle and are particularly frequent in the young patient,

Enhanced MRI is not recommended as a routine method in the young patient (<35 years) with dense breast tissue.

Enhanced MRI should be performed during the second or third week[6-16 days] of the menstrual cycle .

Because diffuse or focal enhancement also may be encountered during postmenopausal hormone-replacement therapy,

Enhanced MRI is not recommended for patients who complain of breast tenderness during hormone-replacement therapy.

If hormone-replacement therapy is discontinued, enhancement subsides after a few months.

MRI TECHNIQUE Breast MRI should be performed

using dedicated breast surface coils.

Most of these are designed such that the patient lies prone with the breasts dependant within the coil.

Most studies are based on examinations performed with 1 to 1.5 T magnets

Some coils are equipped with the capability of applying compression to the breast .

MAMMOGRAPHY MRI Screening modality Cost Effective. Micro calcifications. Not effective in dense

breasts. Not effective post

surgery/radiation.

Screening in dense breasts[high risk]

Screening[post scarring] Implant evaluation Guidance for biopsy Not cost effective.

THE INTERPRETATION OF BREAST MRI Enhancing lesions are divided into three main categories:

focus/foci, masses, areas of non-mass enhancement

Focus (or when multiple, foci) is an area of enhancement measuring less than 5 mm in diameter which is too small to characterize.

A mass is a three-dimensional lesion that occupies a space within the breast. we look at its shape, its margins and its internal characteristics: this includes its T1- and T2-characteristics as well its enhancement pattern.

Non-mass like enhancement are areas of enhancement without a detectable three-dimensional mass. Features of non-mass enhancement include its distribution, its internal enhancement pattern, and whether the enhancement is symmetric or asymmetric.

T2 FAT SUPPRESSED IMAGES High signal on T2-fatsat

T2 fat-suppressed images looking for water. Lesions that are bright on T2 include cysts, lymph nodes and fat necrosis. These are all benign lesions.

Unfortunately there is one malignant lesion that has a high signal intensity on T2 fat-suppressed weighted images. This is the colloid carcinoma.

On the image on the left there are multiple rounded areas in both breasts.These are multiple cysts.

Fibroadenoma (left) and a colloid carcinoma (right). Both are bright on T2WI.

The image on the far left shows a round lesion with bright signal on T2. This is a a fibroadenoma. On the right is an example of a colloid carcinoma in a breast with dense, glandular tissue.

It is the exception to the rule that all things with bright signal on T2 fat-suppressed images are benign.

ENHANCEMENT PATTERN OF A MASS

Homogeneous enhancement is uniform and confluent enhancement throughout the mass. Ex.invasive ductal carcinoma.

Heterogeneous enhancement is non uniform enhancement, which varies within the mass.

Ex. invasive lobular carcinoma

Rim enhancement is enhancement mainly concentrated at the periphery of the mass. This type of enhancement is frequently a feature of high-grade invasive ductal cancer, fat necrosis, and inflammatory cysts. A lesion with rim enhancement that is not a typical cyst has a 40% chance of malignancy.

Dark internal septations refers to non-enhancing septations in an enhancing mass. These are typical for fibroadenomas, especially when the lesion has smooth or lobulated margins.

. Enhancing internal septations are usually a feature of

malignancy.

Central enhancement is pronounced enhancement of a nidus within an enhancing mass. Central enhancement has been associated with high-grade ductal cancer.

Click icon to add picture

NON-MASS ENHANCEMENT Non-mass enhancement is enhancement without three-dimensional characteristics.It is important because it occurs in a significant number of cancers.

The image on the left shows focal non-mass enhancement.This proved to be a focal DCIS.

The image on the left shows linear non-mass enhancement.This proved to be stromal fibrosis.

SPECIFIC BREAST TUMORS

1.Fibroadenoma: a classic fibroadenoma: a

round, smoothly marginated lesion with some black or gray areas on the inside, which are the non-enhancing septations.

2. Cysts: Cysts have a high signal on

T2 fat-suppressed images. After the injection of gadolinium, they will show up as filling defects, sometimes with rim enhancement.

3.Fat containing lesions

The pre-contrast T1, non fat-suppressed sequence can show the presence of fat in a lesion. High signal on a T1-weighted image can be seen in intramammary lymph nodes, fat necrosis and hamartomas.These areas will be dark on fat suppressed images.

4.DCISDCIS typically shows

clumped, ductal, linear or segmental non-mass enhancement.

5. Invasive ductal carcinoma

presenting as a large, homogenously enhancing mass, spiculated mass with rim- enhancement

6.Invasive lobular carcinama Irregularly shaped mass with spiculations and a heterogeneous internal enhancement pattern.

7. inflammatory carcinoma

The image shows a large inflammatory carcinoma with diffuse thickening of the skin.

8.Sarcoma with osseous differentiationpatient with a sarcoma with osseous differentiation, showing less enhancement.

9.Metastatic lymph node

The image shows a large enhancing lymph node on the right.

TEMPORAL RESOLUTION - KINETIC ANALYSIS (CURVES)

Type 1 curve.There is a slow rise and a continued rise with time.

Type 3 curve shows a rapid initial rise, followed by a drop-off with time (washout) in the delayed phase.

Type 2 curve, which is in the middle: a slow or rapid initial rise followed by a plateau in the delayed phase,

MRI - LIMITATIONS Low specificity: benign, malignant, atypical and

proliferative changes enhance.

Variable and heterogeneous background enhancement of normal breast tissue, influenced by phase of menstrual cycle

Limited but growing clinical experience

Time intensive to perform and interpret

MRI FISTULOGRAM

ANATOMY The anatomical anal canal

extends from the perineal skin to the dentate line.

The Surgical anal canal extends from the perineal skin to the anorectal ring.

The anorectal ring lies

approximately 1-1,5 cm above the dentate line. The total length of the surgical anal canal is about 4-5 cm.

CLASSIFICATION

St James’s university hospital classification :

GRADE 1: simple linear inter sphinctericGRADE 2: inter sphincteric with abscess or

secondary trackGRADE 3: trans-sphinctericGRADE 4: trans-sphincteric with abscess or

secondary track within the ischiorectal fossaGRADE 5: supralevator and translevator

extension

Parks classification 1. inter-sphincteric (~70%): fistula

crosses the intersphincteric space2. trans-sphincteric (25%): fistula

crosses from the intersphincteric space

3. supra-sphincteric (5%):  fistula passes superiorly into the intersphincteric space, and over the top of the puborectalis muscle then descending through the iliococcygeus muscle into the ischiorectal fossa and then skin

4. extra-sphincteric (1%): fistula crosses from perineal skin through the ischiorectal fossa and levator ani muscle complex into the rectum 

MRI FISTULOGRAMFistulous tracts are

typically: T1: isointense to

muscle, enhancing with contrast

T2: low signal compared to fat for normal anatomy

T2FS: high signal compared to fat for fistula

MRI ANAL ANATOMY

MRI TECHNIQUE Slice thickness 3-4mm Section Planes1. Axial - relationship to sphincters2.Coronal - level of internal opening andrelationship to levator ani muscles. 3.Sagital may be useful (anovaginalfistula)MRI sequences Anatomical views Sag T2 - Ax T2 Pelvis Fistula imaging STIR ( Short tau inversion recovery) Fat Suppressed T2 Gado Fat suppressed T1

REPORTING OF MRI FISTULOGRAM1.Fistula type2. Internal openingLevel and position

(clockwise)3. Primary fistula

pathway to theexternal openingLocation and hour4. Number and position

of supralevatorian extensions?

5. Number and positions of collections

GRADE 1 SIMPLE INTER-SPHINCTERIC FISTULA

T2W images with and without fat saturation.An intersphincteric fistula is located at 6 o'clock.

CORONAL VIEW

Axial T2-weighted images with fat suppression (STIR :Short tau inversion recovery) at two different levels (a, b). The dotted arrows demonstrate the inter-sphincteric fistula and its extension to the skin (solid arrow)

GRADE 2 INTER-SPHINCTERIC TRACK WITH SECONDARY TRACK OR ABSCESS

GRADE 3 TRANS-SPHINCTERIC FISTULA

On axial T2W-fatsat images of a trans sphincteric fistula with the mucosal opening at 11 o'clock.

GRADE 4 TRANS-SPHINCTERIC FISTULA WITH ABSCESS OR SECONDARY TRACK

Trans-sphincteric Fistula With Abscess or Secondary Track

GRADE 5 SUPRALEVATOR AND TRANSLEVATOR FISTULA

The two tracts in the ischio anal region.The right sided tract runs over the puborectal muscle and the mucosal opening lies at the level of the dentate line(black arrow).

HORSESHOE FISTULA

COMPLEX FISTULA

Two tracts in the left buttock form a single tract (no. 1-2).

This fistula breaks through the external sphincter (no. 4).

COMPLEX FISTULA

In the intersphincteric space it divides again into two tracts (no. 5).One ends blindly in the intersphincteric space (no. 6).The other breaks through the internal sphincter with the mucosal defect at 1 o'clock.

COMPLEX FISTULA

MRI DEFECOGRAPHY

Magnetic resonance (MR) defecography is a special type of MR imaging that produces detailed images during a bowel movement and provides information about the structure and function of the rectum and the pelvic floor , a network of muscles that stretches between the pubic bone and spine and the abdominal organs it supports.

MR defecography helps assess pelvic floor abnormalities that can be difficult to diagnose through physical examination and other tests such as colonoscopy and sigmoidoscopy.

MRI DEFECOGRAPHY

INDICATIONS1. Evaluation of rectal outlet obstruction (obstructed

defecation) symptoms2. Evaluation of all types of rectal (fecal) incontinence.3. Suspected conditions such as internal rectal

intussusception, enterocele, rectocele or sigmoidocele.

4. To compare pre- and post-surgical repair of rectal outlet obstruction (obstructed defecation).

5. Detect non relaxing puborectlalis6. Detect abnormal perineal descent

MRI TECHNIQUE MR defecography may be

performed in either the traditional MRI unit (a large cylinder-shaped tube surrounded by a circular magnet) or in an open unit. In an open MRI unit, two large magnets surround the patient and a removable chair that simulates a toilet is located in the space between the large vertical magnets

Salient phases of MRI Defecography Image captured

During rest with filled anal bulb During maximum contraction of anal

sphincter and pelvic floor muscles During straining without evacuation During evacuation During rest when evacuation is completed

NORMAL MR DEFECOGRAM Normal position of the anorectal junction at

rest (arrow in a) with mild pelvic floor lift on squeeze (B) On straining (C) and defecation (D) there is mild descent of the anorectal junction, with the rectum and anal canal aligned in almost a straight line.

The broken white line in (D) is the pubococcygeal line. The broken black line is the "H line" corresponding to the anteroposterior dimension of the hiatus. The solid black line is the "M line" which is the perpendicular distance between the pubococcygeal line and the posterior anorectal junction

The PCL is drawn from the inferior border of the pubic symphysis to the last coccygeal joint. level of pelvic floor

The H line is drawn from the inferior border of the pubic symphysis to the posterior wall of the rectum at the level of the anorectal junction. AP width of levator hiatus

The M line is drawn perpendicularly from the PCL to the most posterior aspect of the H line. Vertical distance of levator hiatus

Normally, the H and M lines should not exceed 5 cm and 2 cm in length, respectively

Anorectal angle This is the "mid-axial longitudinal axis of the rectum and the anal canal", created by the anterior pull of the puborectalis sling at the level of the anorectal junction. At rest, it is held at 90 - 100°. This becomes more acute (70 - 90°) when the patient contracts the anal sphincters and pelvic floor muscles, and more obtuse (110 - 180°)during defecation.

RECTAL PROLAPSE Pre prolapseRectum is funnel shapedLack of fixation to sacrumExcessive rectosigmoid motilityIntussusception

ProlapseRedudant sigmoid colonWide deep pouch of douglus

RECTOCELE Severe descent of the

anorectal junction with moderate anterior rectocele. Normal position of anorectal junction at rest (A) with normal alignment on straining (B). During defecation (C and D), there is severe descent of the anorectal junction which is located approximately 7 cm below the pubococcygeal line (line 1 in d). Also, note the moderate anterior rectocele where the anteiror rectal wall bulges forward measuring approximately 3 cm in length.

RECTORECTAL INTUSSUSCEPTION Normal position at rest

(A) with moderate anorectal descent on defecation (B). There is evidence of telescoping of the proximal rectum into the distal rectum representing rectorectal intussusception (C and D). Note the classical "arrowhead" configuration of the intussusception

SPASTIC PERINEUM SYNDROME Normal position at rest

(A). During straining (B) and defecation (C), there is persistent prominent indentation of the puborectalis sling on the posterior rectal wall with an acute anorectal angle. (D) shows the acute anorectal angle of approximately 44° (measured between the posterior rectal and anal walls) during defecation

ENTEROCELENormal position at rest (A). During defecation (B and C), there is descent of the peritoneal sac with small bowel loops along the anterior rectal wall representing an enterocele. Also note the bladder and anorectal descent, anterior rectocele, and rectorectal intussusception