Leigh Vaughan, MD June 5, 2012 MUSC. Outline CT Advantages, disadvantages Modality basics Appropriate uses With or without contrast MRI Advantages, disadvantages.

Leigh Vaughan, MDJune 5, 2012

MUSC

OutlineCT

Advantages, disadvantagesModality basicsAppropriate usesWith or without contrast

MRIAdvantages, disadvantagesMRI PhysicsWith or without contrastT1, T2, Flare, diffusion

Anatomy TutorialResources and References

CT BasicsBenefits: More accessible

Less expensive compared to MRI

Disadvantage: More hazardous radiation exposure Risk of nephrotoxicity or

adverse reaction with IV contrast Motion or metal artifact

Display: Transverse images view with right of patient on the left (“foot of bed” view)

CT BasicsTypes: helical or spiral, multiplanar reformating, ultrafast (electron beam)

Resolution: varying thickness from 1mm to 10mm, with varying intervals (high res 8-10mm)

Measurements: Tissue density measured in Hounsefield units (-1000 to +1000); the more negative the HU, the blacker the image, the less dense the object

Reading: High attenuation or density= white & low attenuation or density= black

CT WindowsLung Window- parenchyma, bronchial anatomy. Negative HU

Increased opacity: consolidation, collapse, mass, interstitial disease, pleural disease

Decreased opacity: destroyed parenchyma (emphysema, bullae, cyst) decreased blood or air flow (infarct, emboli, pneumothorax)

Mediastinal Window- hilar, pleural, & mediastinal anatomy

Increased opacity: LN, hematoma, goiter, massDecreased opacity: pneumomediastinum

Bone Window- Most dense, highest HU

Lung window

Indications for ContrastWith ContrastIV: vasculature (evaluation of PE, aortic dissection)

pancreatitisbrain abscess avascular tissue lymph tissue pleural diseasetumor delineation

PO: non-intestinal abdominal structures (abscess, mass)

Without ContrastUses: pulmonary nodules

renal stone*sinus disease

hydrocephalus acute stroke

(unknown type)*traumacalcium scoring in

CAD interstitial disease (HIGH RES)

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MRI BasicsAdvantages: No ionizing radiation

Safer in pregnancy Better soft tissue contrast

Disadvantages: More expensive Less available Unsuitable in unstable or claustrophobic Unsuitable with foreign objects

(aneurysm clips, pacers, cochlear implant, cardiac stents, shrapnel)

Not optimal for bone

Precautions: Remove transdermal patches (aluminum)

MRI PhysicsMRI machine uses strong magnetic field to detect

the location and local chemical environment of protons in water molecules

T1/T2 relaxation times- the time it takes for nuclei to return to its original alignment in longitudinal (T1) or transverse (T2) axis of the magnetic field

Use “signal” when speaking about tissue (rather than “density” used with CT’s)

Planes: sagittal, axial, coronal

MRI With or Without ContrastContrast with GadoliniumGadolinium slows down relaxation phase (shorten

T1) & increases signal on T1 weighted images- relatively more contrast goes to vascular structures, producing increase in T1 weighted signal intensity

Water/pathological areas appears brighter on T1 contrast.

Contrast contraindicated in ESRD requiring renal replacement (not recommended with GFR < 30)

MRI: T1 & T2T1 ANATOMY– longitudinal tissue relaxation -water (CSF,

urine) is dark/ fat is bright

T2 PATHOLOGY– transverse tissue relaxation -water (CSF, urine) is bright/ fat is darkGood to establish edema (white or increase signal)Distinguish pathologic tissue from normal

T2 with FLAIR (which speeds up imaging time)- - most helpful in multiple sclerosis/demyelinating-free water is now dark, but edematous tissues remain bright.

Diffusion weighted imagesImages reflect random motion of waterMost helpful in evaluation of early, acute stroke

(<6 hrs)In acute stroke, there is decrease water

diffusion/motion, injured tissue appears whiteImages can be shown in ADC maps (apparent

diffusion coefficient ) which reverses the signal (ie. acute stroke is then black)

CT Radiology Anatomy TutorialChest:http://www.upstate.edu/cdb/education/grossanat/ThoraxT2nlabeled.htmlhttp://www.upstate.edu/cdb/education/grossanat/ThoraxT4-5nlabeled.htmlhttp://www.upstate.edu/cdb/education/grossanat/ThoraxT8-9nlabeled.html

Abdomen and Pelvishttp://www.upstate.edu/cdb/education/grossanat/ab2nlabeled.htmhttp://www.upstate.edu/cdb/education/grossanat/ab3nlabeled.htm

Headhttps://www.radiology.wisc.edu/education/med_students/neuroradiology/NeuroRad/NeuroRad.htm

Other referenceshttp://www.radiologyeducation.com/Textbooks, online e-tools, website links, journals, student and resident specific material, & CME

Anatomy tutorial: http://ect.downstate.edu/courseware/rad-atlas