A CT scan is most beneficial for observing bone structure, and is less useful for scanning soft tissues in the body. To scan these tissues more effectively, a doctor will usually suggest an MRI scan. MRI stands for Magnetic Resonance Imaging. Rather than using radiation, this procedure exposes the body to a strong magnetic field, which affects the molecules in the body in such a way that a detailed picture can then be produced.
| Attribute | CT Scan | MRI scan |
|---|
| About | CT Scan or Computed tomography is a medical imaging obtained using X-rays. The radiation is passed through the body and received by a detector and then integrated by a computer to obtain a cross sectional image that is displayed on the screen | Magnetic resonance imaging (MRI) is a medical imaging technique most commonly used in radiology to visualize detailed internal structure of the body.,because of better soft tissue resolution. |
| Effects | Despite being small, CT can pose the risk of irradiation. | No biological hazards have been reported with the use of the MRI. |
| Principal used for imaging | Uses X-rays for imaging | Uses radio waves and magnetic field |
| Time taken for complete scan | Usually completed in 5 mins | Usually completed in 20 mins |
| Types of Scanners | Multislice scanners offer reduced examination times and more importantly employ thin sections and improved resolution. Advanced applications can be done only on Multislice scanner. | 1.5 Tesla MRI-Higher magnetic field strength contributes high quality images, thinner slice thickness and potentially earlier and better detection of pathology. Advanced applications improves diagnosis. |
| Advanced Applications | Cardiac CT, Denta Scan, Multiphasic Liver scan, Angiographies, 3 D imaging of bones,High resolution scan of thorax. | Spectroscopy,Diffusion tensor imaging,Breast MRI,Non contrast Angio,MRI Urography ,MRCP & Cardiac Imaging |
Brain
| Clinical Problem | Preferred Modality | Contrast | Comments |
|---|
| Head injury: SDH/ EDH/ SAH/Fractures | CT | No | Faster imaging technique. |
| Diffuse axonal injury | MRI | No | Deep seated, microhemorrhages are detected. |
| Stroke | MRI > CT | No | MRI detects infarcts in the hyperacute stage before it can be seen by any other modality. Angiography provides additional information about the thrombosis of the vessel involved |
| Tumors | MRI | Yes | Multiplanar imaging-Better delineation of the extent and spread. MR spectroscopy- provides details about the metabolite contents of lesion ,which may help in differentiating infection from neoplasm. |
| Seizures | MRI | Â | Provides better details of brain structure than any other modality. Images are helpful for identifying areas of scar tissue, abnormal development (dysplasia), and also changes in the brain white matter. |
| Headache | MRI with ANGIO and VENOGRAM | Â | Additional information is obtained like venogram and angiogram and that too without contrast. |
| CNS Infections | MRI | Yes | Â |
| Dementia/ Neurodegenerative Disorders | MRI | +/- | Â |
| Pituitary lesions | MRI | Yes | Dynamic contrast evaluation helps in detecting small pituitary microadenomas |
Spine
| Clinical Problem | Preferred study | Contrast | Comments |
|---|
| Herniated Disc, Cervical or Thoracic | MRI | No | The disc, nerves and spinal cord can be seen clearly and in multiple planes. |
| Herniated Disc, Lumbar | MRI | If previous surgery, contrast | Contrast essential to distinguish scar from recurrent disc prolapse after surgery |
| Canal Stenosis | MRI >> CT | No | Â |
| Metastasis: Bone Epidural Intraspinal | MRI | Yes | Â |
| Benign Fracture v/s Pathological Fracture | MRI/CT | +/- | MRI allows evaluation of bone marrow, CT for operative planning. |
| Cord Disease | MRI | Yes | Demyelination, Syrinx,Vascular abnormalities can be easily appreciated |
| Cord tumor | MRI | Yes |
Neck, Skull base, Orbit
| Clinical Problem: | Preferred study | Contrast | Comments |
|---|
| Sinusitis | CT | No | CT defines ostial obstruction, bone changes |
| Neck mass | MRI > CT | Yes | Tongue and perineural skull base disease better on MRI |
| Hearing loss, conductive | CT | No | Mastoid, middle ear,ossicles are better seen on CT. |
| Hearing loss, sensorineural | MRI | Yes | Cranial nerves are well delineated. |
| Skull base | MRI = CT | Yes | CT sometimes necessary to better show bony detail. |
| Vocal cord paralysis | MRI >> CT | Yes | Evaluating focal lesions from skull base to carina. |
| Orbit—Proptosis | CT or MRI | Yes | No contrast for graves’ disease. |
| Optic nerves pathology | MRI >> CT | Yes | MRI – optic neuritis. |
| Cavernous sinus pathology | MRI | Yes | MRI brain/sella |
| Cranial nerves pathology | MRI | Yes | Â |
| Facial trauma | CT | No | Bony detail better appreciated |
| Salivary gland | MRI/CT | Yes | Calcification and microcalculi better seen on CT MRI for ductal abnormalities, tumors, infections |
Breast Imaging
| Clinical Problem | Preferred study | Contrast | Comments |
|---|
| Screening in high risk patients | MRI | Yes | Lesion detection is far more superior in patients with negative or nonspecific findings on mammography |
| Staging of Breast Cancer | MRI | Yes | To know the extent and infiltration. |
CHEST
| Clinical Problem | Preferred study | Contrast | Comments |
|---|
| Pulmonary embolus | CT angiography | Yes | Â |
| Nodule, Mass, infiltrate. | CT | Yes | Lung Parenchyma better evaluated on CT. |
| Interstitial Lung Disease | High resoluÂtion CT | No | Thin slices help in identifying distribution of smallest of the nodules |
| Mediastinal/ Vascular Pathology | MRI / CT | Yes | Â |
MUSCULOSKELETAL
| Clinical Problem | Preferred study | Contrast | Comments |
|---|
| Joint Imaging | MRI | No | Excellent details of intra-articular structures like cartilage and ligaments. |
| Fractures | CT / MRI | No | Â |
| Spinal Trauma | MRI preferred for spinal cord evaluation. | No | Fracture fragments better depicted on CT. |
| Bone Tumors | MRI | Yes | The tumors are well delineated and the extent of bone marrow involvement is better seen. |
ABDOMEN/PELVIS
| Clinical Problem | Preferred study | Contrast | Comments |
|---|
| Non-focal pain | MRI = CT | +/- | Contrast for solid organ disease. |
| Focal organ pathology | MRI / CT abdomen | +/- | Multiphasic scan suggested for liver lesions. |
| Gall Bladder/ Pancreatic Pathology | MRI | +/- | Biliary tree can be evaluated without contrast for any stones or strictures |
| Appendicitis, Diverticulitis. | CT abdomen and pelvis | Oral contrast, +/- I.V contrast | Â |
| Painful Hematuria | CT abdomen and pelvis | +/- | Detection of ureteric calculus. CT IVP to evaluate renal function. |
| Painless Hematuria | CT/MRI abdomen | +/- | Â |
| Renal mass | MRI/ CT abdomen | Yes | Â |
| Cancer patient/Metastasis screening | Whole body metastasis screening by MRI. | +/- | Â |
| Adrenal gland | MRI > CT | Â | Contrast only if non-contrast study is inconclusive |
Pelvis:Female
Staging of gynaecological malignanciesPelvis:Male
For prostate and other pelvic pathologies | MRI MRI | Benign lesions of pelvis including fibroids, dermoids and endometriosis can be well evaluated due to excellent soft tissue differentiation on MRI. MRI is now the examination of choice for staging mostmalignancies owing to its multiplanar capability. |
