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Home التعليم الطبي المستمر تعليم أطباء طب وجراحة العيون
MRI in Ophthalmic practice

MRI in Ophthalmic practice

Dr.Reda Gomah El Garia by Dr.Reda Gomah El Garia
19 فبراير، 2022
in تعليم أطباء طب وجراحة العيون
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المحتويات إخفاء
1 MRI in Ophthalmic practice ✍️✍️✍️✍️✍️✍️
2 ✅ Indications of MRI in Ophthalmic practice
3 ✅ Method of MRI in Ophthalmic practice
4 ✅ Interpretation of MRI in Ophthalmic practice
5 ✅ MRA
6 ✍️ MRV • is similar to MRA, but the imaging is gated to the speed of venous flow. • It is useful in identifying cerebral sinus venous thrombosis • It is therefore commonly performed for investigation of papilloedema
7 MRI in Ophthalmic practice Videos :
7.1 Magnetic Resonance Imaging (MRI) video

MRI in Ophthalmic practice ✍️✍️✍️✍️✍️✍️

✍️ Tissue exposed to a short electromagnetic pulse with rearrangement of its hydrogen nuclei. 

✍️ When the pulse subsides, the nuclei return to their normal resting state and reradiating some energy they have absorbed. 

✍️ Sensitive receivers pick up this electromagnetic echo. 

✍️ T1 and T2 times are two complex parameters that depend on proton density, tissue components, and their magnetic properties 

✍️ T1 relaxation is measured using a time constant called T1 in millisecond And defined as the time when 63% of the longitudinal magnetization has recovered

✍️ T2 relaxation is measured using a time constant called T2 in millisecond and defined as the time when 63% of the transverse magnetization has decayed

✍️ T1-weighted imaging 
• differentiate anatomical structures mainly on the basis of T1 values
• Tissues with high fat content (white matter) appear bright and compartments filled with water (CSF) appears dark. This is good for demonstrating anatomy.

T-weighted MRI
T-weighted MRI

✍️ T2-weighted imaging 

• differentiate anatomical structures mainly on the basis of T2 values

• Compartments filled with water (CSF ) appear bright and tissues with high fat content (white matter) appear dark. 

• This is good for demonstrating pathology since most (not all) lesions are associated with an increase in water content.

MRI in Ophthalmic practice
MRI in Ophthalmic practice

✅ Indications of MRI in Ophthalmic practice

✍️ Orbital masses or tumours.

✍️ Optic nerve tumours such as glioma or meningioma.
✍️ Intracranial extension of orbital tumours.

✍️ Suspected compressive optic neuropathy.

✍️ In retrobulbar neuritis, the presence of multiple white matter plaques is predictive of the development of clinical multiple sclerosis (MS).

✍️ Suspected lesions of the chiasm such as pituitary tumours.

✍️ Intracranial aneurysms.

MRI Types
MRI Types

✅ Method of MRI in Ophthalmic practice

✍️ Conventional sequences are T1 and T2 weighted. 

✍️ Protocols are determined by the examining radiologist, based on the clinical situation. 

✍️ Orbital imaging uses specialized fat suppression techniques, which is useful for optic nerve visualization, usually masked by the high signals from orbital fat.

✍️ Diffusion weighted, or diffusion tensor, MRI sequences (image Brownian motion within tissues) were initially found to be useful in acute strokes. 

✍️ More recently, the technique has been shown to be useful for intracranial abscesses and distinguishing an epidermoid from an arachnoid cyst.

✍️ IV paramagnetic gadolinium is used as contrast

✍️ Gadolinium-enhanced scans are useful in the detection of blood–brain barrier abnormalities, inflammatory changes, and increased vascularity.

✍️ In tumour staging around the skull base and orbits, CT and MRI are often complementary.

✅ Interpretation of MRI in Ophthalmic practice

✍️ Always review your own scans in conjunction with the radiology team.

✍️ It is also important to consider the quality of the scan ( adequate slices, appropriate use of contrast or processing especially when unexpectedly normal 

✅ MRA

✍️ MRA is a non-invasive method of imaging the intra and extracranial carotid and vertebrobasilar circulations. 

✍️ The principle of the computerized image construction is based on the haemodynamic properties of flowing blood, rather than on vessel anatomy.

✍️ Demonstrates abnormalities such as stenosis, occlusion, AVMs, and aneurysms.

✍️ MRA is usually a static evaluation however, time-resolved MRA can be useful, as it highlights the separate arterial and venous supplies to an intracranial AVM.

✍️ Disadvantages 
• Cannot detect aneurysms <5mm in diameter 
• long acquisition time 
• suboptimal detection of intravascular calcifications.

✍️ MRV 
• is similar to MRA, but the imaging is gated to the speed of venous flow. 
• It is useful in identifying cerebral sinus venous thrombosis 
• It is therefore commonly performed for investigation of papilloedema

MRI in Ophthalmic practice Videos :

Magnetic Resonance Imaging (MRI) video

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