MRI Internal Auditory Meatus(IAM'S)
Indications for internal auditory meatus(iams) MRI scan
- Sensorineural hearing loss (SNHL)
- Acoustic neuroma
- Ringing in the ears
- Dizziness
- Fullness
- Tumour
- Trauma
- Tinnitus
- Vertigo
Contraindications of internal auditory meatus (iams) MRI scan
- Any electrically, magnetically or mechanically activated implant (e.g. cardiac pacemaker, insulin pump biostimulator, neurostimulator, cochlear implant, and hearing aids)
- Intracranial aneurysm clips (unless made of titanium)
- Pregnancy (risk vs benefit ratio to be assessed)
- Ferromagnetic surgical clips or staples
- Metallic foreign body in the eye
- Metal shrapnel or bullet
Patient preparation internal auditory meatus(iams) MRI scan
- A satisfactory written consent form must be taken from the patient before entering the scanner room
- Ask the patient to remove all metal objects including keys, coins, wallet, cards with magnetic strips, jewellery, hearing aid and hairpins
- If possible provide a chaperone for claustrophobic patients (e.g. relative or staff )
- Contrast injection risk and benefits must be explained to the patient before the scan
- Gadolinium should only be given to the patient if GFR is > 30
- Offer earplugs or headphones, possibly with music for extra comfort
- Explain the procedure to the patient
- Instruct the patient to keep still
- Note the hight and weight of the patient
Positioning
- Head first supine
- Position the head in the head coil and immobilise with cushions
- Give cushions under the legs for extra comfort
- Centre the laser beam localiser over the glabella
Recommended MRI IAM'S Protocols, Parameters and Planning
localiser
A three-plane localizer must be taken at the beginning to localize and plan the sequences. Localizers are usually less than 25 seconds and are T1-weighted low-resolution scans.
T2 tse axial 5mm
Plan the axial slices on the sagittal plane and position the block parallel to the genu and splenium of the corpus callosum. Verify the planning block in the other two planes and ensure that an appropriate angle is maintained in the coronal plane, making it perpendicular to the line of the midline of the brain and the 4th ventricle. Ensure that the number of slices is sufficient to cover the entire brain from the vertex to the line of the foramen magnum.
Parameters
TR 3000-4000 | TE 100-120 | SLICE 5MM | FLIP 130-150 | PHASE R>L | MATRIX 320X320 | FOV 210-230 | GAP 10% | NEX(AVRAGE) 2 |
T2 TSE coronal 3mm
Plan the coronal slices on the axial plane and angle the planning block parallel to the line along the right and left Internal Auditory Meatus (IAMS) (as shown in the diagram). Verify the planning block in the other two planes. Ensure an appropriate angle is maintained in the sagittal plane, parallel to the brain stem. The number of slices should be sufficient to cover the IAMS from the posterior border of the sphenoid sinus up to the line of the fourth ventricle.These coronal T2 scans are performed to aid in the planning of axial 3D scans.
Parameters
TR 3000-4000 | TE 110 | FLIP 130 | NEX 2 | SLICE 3MM | MATRIX 256X256 | FOV 150-180 | PHASE R>L | GAP 10% | SLICE 10-20% |
3D SPACE (3D CISSor 3DFIESTA) axial .5mm
Plan the axial slices on the coronal plane and angle the planning block parallel to the line along the right and left internal auditory meatus (IAMS), as shown in the diagram. Verify the planning block in the other two planes. Ensure an appropriate angle is maintained in the sagittal plane, perpendicular to the brain stem. The number of slices should be sufficient to cover the IAMS from the hippocampus up to the line of the C1 vertebral body.
Parameters CISS
TR 12-15 | TE 6-7 | SLICE .8mm | FLIP 80 | PHASE R>L | MATRIX 384X320 | FOV 210-230 | GAP 10% | NEX(AVRAGE) 1 |
T1 pre contrast and post contrast scans are only required in case of tumor present in internal auditory canal.
T1 TSE coronal 2mm
Plan the coronal slices on the axial plane and angle the planning block parallel to the line along the right and left Internal Auditory Meatus (IAMS) (as shown in the diagram). Verify the planning block in the other two planes. Ensure an appropriate angle is maintained in the sagittal plane, parallel to the brain stem. The number of slices should be sufficient to cover the IAMS from the posterior border of the sphenoid sinus up to the line of the fourth ventricle.These coronal T2 scans are performed to aid in the planning of axial 3D scans.
Parameters
TR 400-500 | TE 15 | FLIP 150 | NXA 4 | SLICE 2MM | MATRIX 256X256 | FOV 150-180 | PHASE R>L | GAP 10% | SLICE 10-20% |
T1 TSE axial 2mm
Plan the axial slices on the coronal plane and angle the planning block parallel to the line along the right and left internal auditory meatus (IAMS), as shown in the diagram. Verify the planning block in the other two planes. Ensure an appropriate angle is maintained in the sagittal plane, perpendicular to the brain stem. The number of slices should be sufficient to cover the IAMS from the hippocampus up to the line of the C1 vertebral body.
Parameters
TR 400-600 | TE 150 | SLICE 2mm | FLIP 90 | PHASE R>L | MATRIX 256X256 | FOV 170-180 | GAP 10% | NXA(AVRAGE) 4 |
