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 (<6 hrs)
 In acute stroke, there is decrease water diffusion/motion,
injured tissue appears white
 Images can be shown in ADC maps (apparent diffusion
coefficient ) which reverses the signal (ie. acute stroke is
then black)
CT Radiology Anatomy Tutorial
Chest:
http://www.upstate.edu/cdb/education/grossanat/ThoraxT2nlabeled.html
http://www.upstate.edu/cdb/education/grossanat/ThoraxT4-5nlabeled.html
http://www.upstate.edu/cdb/education/grossanat/ThoraxT8-9nlabeled.html
Abdomen and Pelvis
http://www.upstate.edu/cdb/education/grossanat/ab2nlabeled.htm
http://www.upstate.edu/cdb/education/grossanat/ab3nlabeled.htm
Head
https://www.radiology.wisc.edu/education/med_students/neuroradiology/NeuroRad/Neur
oRad.htm
Other references
http://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