CT v. MRI

Part 1

Back 2 Basics

▪Two types of Interactions▸Ionization▸Excitation

Ionization

▪Caused by adding or subtracting electrons from an atom▪In radiology, normally subtracted electrons

▪Most radiology modalities require ionization▸Compton effect - CT▸Photoelectric effect – Radiology

▪Permanent changes to the atom▪May manifest as abnormalities

Excitation

▪Caused by adding energy to the atom▪Most common side-effect is heat▪If stimulation stops before causing damage; there is no long

term effect or damage▪MRI is uses excitation to generate images

Advantages of CT

▪Low cost

▪No contraindicated patients ▸(except for contrast)

▪Fast

▪In some body systems fewer motion artifacts

Advantages of MRI

▪Multi-planar capability▸Coronal, sagittal, and oblique

▪Vascular info without contrast

▪No bone artifacts

▪Some functional information is available

Disadvantages

▪CT▸Requires radiation

▪MRI▸Some patients are completely contraindicated

Neurologic Anatomy

▪Brain▸Cerebrum, cerebellum, and brain stem

▪Spine▸Bony anatomy and cord anatomy

CT uses in Neuro Imaging

▪Acute bleeds▸Traumatic v. hemmorhagic

▪Fractures

▪Bony erosion

MRI uses in Neuro Imaging

▸Tumors▸Infections▸Non-specific events▸Diseases and syndromes

Stroke

▪Initial exam▸CT eliminates hemmorhagic CVA

▪MRI is good for accurate assessment▸Diffusion MR - extent of damage

Bleeds

▪SAH

▪SDH

▪Epidural

▪Intracerebral

Metastatic disease

▪CT▸Can be difficult to see

▪MRI▸Proper sequencing may affect diagnostic ability

Spine Mets

▪Often called the only emergent MRI

▪Tumors that metastasize to the bone▸Prostate▸Breast

Acoustic Neuroma

▪CT▸Relies on bony erosion▸Can be difficult due to artifacts

▪MRI▸Multi-planar▸No artifacts▸Can utilize contrast

Pediatric Glioma

▪CT▸Difficult visualization

▪MRI▸Differentiate between tumor and edema

Multiple Sclerosis (MS)

▪CT▸Limited

▪MRI▸Good visualization

Syrinx

▪CT▸Limited by the axial plane

▪MRI▸Direct sagittals▸Find underlying cause

Arnold Chiari Syndrome

Neurofibroma

▪CT▸Limited by plane and artifacts

▪MRI▸Direct imaging▸Improves with contrast

Cervical Spine Fractures

▪CT▸Good bony information

▪MRI▸Soft tissue info and cord damage

Fractures

▪Facial▸Tripod▸Blow-out

▪Cranial▸Depressed

Aneurysm

▪CT▸Requires contrast▸Decreased resolution with reconstructions

▪MRI▸No contrast required▸Multi-planar acquistion

Herniated Nucleus Pulposa (HNP)

▪CT▸Depends on patient and location

▪MRI▸Direct sagittal▸Good post evaluation

Conclusion

▪Both MR and CT have a place in the modern radiology department. The key is the proper and accurate use of the correct modality.