MRI vs CTThe Differences of these modalities

and which one is best suited

Basic Anatomy of viewing plane

• The Image Planes

• Axial (Cross-section)

• Slice of bread

• either direction

• Sagital (Midline)

• Left <-> Right

• Coronal (Horizontal)

• Front <-> Back

Computerized Axial Tomography

• The Mechanics

• Tomography - one direction of motion, various focal planes.

• Axial Tomo - One dynamic motion coupled with movement of subject.

Computerized Axial Tomography

• Cross-sectional imaging using X-Rays

• Acquires images extremely fast (mSec)

• Accuracy to 1mm (thin slices)

• SNR - low

• Motion sensitivity - low

• Fast Image reconstructions

Computerized Axial Tomography

• Great for imaging:

• Bone

• Lung

• Calcifications

• Heart

• Vessels (Arterial & Venous)

• Soft Tissue (with vessels)

• 3D reconstructions

Computerized Axial Tomography

• Limitations and Risks:

• Not good for Pregnancy, Kids, Sensitive Tissue (Post RTX)

• Contrast needed for imaging vessels, but low probability to cause Nephrological Toxicity

• Weight limit of 400-450 lbs

Magnetic Resonance Imaging

• The Mechanics

• Super-Conductor

• Helmholtz Coil

Helmholtz CoilHermann von Helmholtz (1821-1894)German scientist and philosopher who made fundamental contributions to physiology, optics, electrodynamics, mathematics, and meteorology.Helmholtz CoilsA pair of conducting circular coils each having N turns, each carrying a current I, separated by a distance equivalent to the radius of the circular loops, produce a homogeneous magnetic field B in the mid-plane between the two circular coils.

a = radius of the coilsa = separation between the coilsa/2 = distance to the mid-planeB = magnetic field at the mid-plane

Magnetic Resonance Imaging

• The Mechanics

• Coils and Gradients

• RF Transmitter &

• Receivers

Magnetic Resonance Imaging

• Uses Magnetic Fields and RadioFrequency devices for acquiring images

• Imaging in any plane (X,Y,Z)

• Image time varies significantly (30sec - 45min)

• Very sensitive to Motion

• Accuracy within 1.5mm (but with many compromises and only on specific Sequences)

• Image reconstruction more time consuming

Magnetic Resonance Imaging

• Great for Imaging:

• Soft Tissue (more information than CT)

• Ligaments, Tendons, Spinal Cord

• Bone Tumors & minute abnormalities

• Vessels

Magnetic Resonance Imaging

• Limitations and Risks:

• Not good for Pacemaker, Aneurysm clips, Metal implants, Cochlear implants, etc.

• High Anxiety component

• Very sensitive to motion (time variant)

• Weight limit 300-350 lbs

• Not good for Lung or Heart Imaging

• Contrast not always needed, but higher Nephrological Toxicity

GE CT Scanner

GE MRI Magnet

GE Head Coil

GE Knee Coil (Solid)