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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 Arnold Chiari Syndrome ▪ CT ▸Limited by the axial plane ▪ MRI ▸Direct sagittals ▸Find underlying cause 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.
