MRI & CT Flashcards
Why are advanced imaging modalities like CT and MRI necessary?
They provide better resolution & visualisation of soft tissues & complex anatomical structures compared to standard radiograph
How does CT imaging work?
CT takes multiple X-ray slice images to reconstruct a detailed 3D view of structures
What are the benefits of CT imaging?
Excellent bone detail
Allows for curved & slice reconstructions
Can be enhanced with contrast agents
Quick
What are the disadvantages of radiography & CT?
Radiation dosing
Relatively poor soft tissue resolution
What are the key differences between radiography and CT?
Radiography: Uses shadow projection through tissue, creating -ve image based on radiodensity
CT: Uses rotating X-ray tube & receiver to capture multiple images in different orientations, reconstructed into 3D dataset for slice imaging
Both rely on radiodensity but CT provides greater anatomical detail
How does MRI imaging work?
MRI uses strong magnetic fields & radio waves to create detailed soft tissue images without ionising radiation
the different physical properties of protons allow us to produce different sets of contrast
What are the different MRI sequences and their applications?
T1-weighted: Good for anatomical detail
T2-weighted: Highlights fluid & soft tissue
T1 post-contrast FS: Enhances structures after contrast administration
FLAIR T2: Suppresses cerebrospinal fluid for better lesion visibility
T2 Gradient Echo:* Detects haemorrhage
Black blood angiography: Highlights vascular structures
Fill in the table comparing T1 to T2 MRI
What are some limitations of MRIs?
Sensitive to movement artefacts
Poor bone detail compared to CT
Susceptible to metallic artefacts
Incompatible with implanted medical devices
Slower than CT
What types of contrast media are used in CT & radiography?
Positive contrast: Radiodense materials like iodine & barium
Negative contrast: Radiolucent materials like air
What types of contrast media are used in MRI?
Positive contrast: high signal materials like gadolinium
Negative contrast: low signal materials like air
When should CT be preferred over MRI?
When detailed bone imaging is needed
When speed is priority (e.g., trauma cases)
When MRI is contraindicated due to metal implants
When should MRI be preferred over CT?
When soft tissue detail is needed (e.g, neurological cases)
When avoiding radiation exposure is important
When evaluating fluid-filled structures like brain & spinal cord
What are the major differences between MRI and CT?
CT: Better for bone detail, faster imaging, good for trauma cases.
MRI: Better for soft tissue, no ionising radiation, but more prone to movement artefacts
CT uses iodine-based contrast, MRI uses gadolinium-based contrast
What are the different CT contrast imaging techniques?
CT myelogram: Uses contrast injected into the CSF
Pre-contrast & post-contrast imaging: Helps differentiate normal from abnormal tissue
What are the health and safety considerations for CT and MRI?
CT: Uses ionising radiation, which requires proper radiation safety measures
MRI: Uses strong magnetic fields, which can pose risks for implanted medical devices, metallic implants, missile hazards & magnetic media
Why is applied anatomy important in spinal imaging?
Understanding normal spinal anatomy is crucial for differentiating normal structures from pathological changes in CT & MRI images
How does software reconstruction aid in spinal imaging?
It allows for 3D reconstructions & multiplanar reformatting of CT & MRI images, improving visualisation of spinal pathology
What is going on in this CT image?
Calcified disc extrusion
condition where calcified disc material extrudes into vertebral column, compressing spinal cord
On midline sagittal slice, calcified material is visible within vertebral column
On transverse slice, calcified material may occupy up to 2/3 of spinal canal
How can we differentiate calcified disc extrusion from other conditions?
Main differential diagnoses include new bone growth, calcified neoplasia, or extruded disc material
History helps differentiation:
- Calcified disc extrusion: Acute onset
- Neoplasia or new bone formation: Progressive onset
How does C1 vertebral arch neoplasia present on imaging?
C1 vertebra normally forms ring-shaped structure.
On imaging, tumour may cause osteolysis & distortion of dorsal aspect of arch
Tumour leads to marked expansion & destruction of cortical layers, suggesting neoplastic process rather than infection
What is going on in these CT images?
Discospondylitis
- infectious or inflammatory process affecting intervertebral disc & adjacent vertebrae
Presents as osteodestruction crossing from one bone to another, which is uncommon in primary neoplasia but typical for infections like osteomyelitis.
CT Findings: Osteolysis at vertebral end plates, new bone formation as reactive process
How do spinal tumours present on MRI imaging?
MRI allows visualisation of soft tissue structures
Tumour may cause extradural compression of spinal cord, appearing as mass displacing spinal cord to one side
In transverse sections, spinal cord may initially be difficult to distinguish but progressively appears compressed & distorted
What is going on in this MRI?
Fibrocartilaginous Embolisation
- vascular lesion that causes ischemia or oedema within spinal cord
Unlike tumours, FCE does not cause expansion of spinal cord
MRI Findings: focal area of high signal intensity within spinal cord on T2-weighted images
Duramater & subarachnoid space remain intact, indicating no significant mass effect
