Without Contrast - Clinical Departments

Leigh Vaughan, MD June 5, 2012 MUSC

Outline  CT  Advantages, disadvantages  Modality basics  Appropriate uses  With or without contrast

 MRI  Advantages, disadvantages  MRI Physics  With or without contrast  T1, T2, Flare, diffusion

 Anatomy Tutorial  Resources and References

CT Basics Benefits: 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 Basics Types: 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 Windows Lung 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, mass  Decreased opacity: pneumomediastinum Bone Window- Most dense, highest HU

Mediastinal window, with contrast

Lung window

Indications for Contrast With Contrast  IV: vasculature (evaluation of PE, aortic dissection) pancreatitis brain abscess avascular tissue lymph tissue pleural disease tumor delineation

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

Without Contrast Uses: pulmonary nodules renal stone* sinus disease hydrocephalus acute stroke (unknown type)* trauma calcium scoring in CAD interstitial disease (HIGH RES)

Gallstone-induced pancreatitis in 27 year-old woman

Balthazar, Emil J. Radiology. 2002; 223: 603-613

Copyright © 2002 by RSNA

MRI Basics Advantages: 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 Physics  MRI 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 Contrast  Contrast with Gadolinium  Gadolinium 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 & T2  T1 ANATOMY– longitudinal tissue relaxation -water (CSF, urine) is

dark/ fat is bright

 T2 PATHOLOGY– transverse tissue relaxation -water (CSF, urine) is

bright/ fat is dark  Good 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 images  Images reflect random motion of water  Most helpful in evaluation of early, acute stroke (