Introducing cross- sectional imaging Dr.Ahmed S. Tawfeek FIBMS(Rad.)

Introducing cross sectional imaging z CAT principal CAT principal z CAT comparisons CAT comparisons z MRI principle MRI principle z MRI comparisons MRI comparisons MRI

Computerized Axial Tomography (CAT) Using CT scanners shows sections of the body resembling anatomical sections Generally, images are obtained in the transverse plane

Computerized Axial Tomography (CAT) In this process a small beam of x- ray is passed through a plane of the body while the x-ray tube moves in an arc or a circle around the body

Computerized Axial Tomography (CAT) The amount of radiation absorbed by different elements of the chosen plane varies

Computerized Axial Tomography (CAT) A computer stores a large amount of data from a selected region of the body, making it possible to determine the spatial relationship of the radiation-absorbing structures within it

Computerized Axial Tomography (CAT) Important diagnostic information about tissues in the scanned regions of interest is thereby made Contrast enhancement may be used Contrast enhancement of the bowel after oral administration of barium

Computerized Axial Tomography (CAT) Sections are visualized as if you were looking at cross sections from below with the right side to your left rightleft liver spleen liver

Comparisons Cross section CAT image head

Comparisons Cross section CAT image thorax

Comparisons Cross section CAT image abdomen

Cross-sectional imaging zMagnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging (MRI) Uses non-ionizing radiation and has no demonstrated adverse biological effects. Magnetic resonance images can be obtained in any tissue plane transverse sagitttal coronal

Magnetic Resonance Imaging (MRI) The appearance of an MR image is a function of the chemical composition of the various types of tissue bone fat muscle

Magnetic Resonance Imaging (MRI) At the atomic level, water and adipose are composed of hydrogen, oxygen, carbon, and phosphorus atoms. The hydrogen atom contains a proton and an orbiting electron. A spinning charged particle (the proton) produces a local magnetic field

Magnetic Resonance Imaging (MRI) In the absence of any external forces, the magnetic moments of protons in tissue are oriented randomly

Magnetic Resonance Imaging (MRI) If the protons are placed in a strong magnetic field, their magnetic dipoles align with and against the strong magnet

Magnetic Resonance Imaging (MRI) Slightly more than half of the magnetic moments align parallel to the field, because it takes less energy for the small magnetic moments to align with the stronger main magnetic field

Magnetic Resonance Imaging (MRI) This slight excess of protons in the lower energy state, whose individual magnetic moments add up, creates the net magnetization and causes the patient to acquire a slight magnetism

Magnetic Resonance Imaging (MRI) Magnetic resonance imaging (MRI) combines a strong magnetic field and radiofrequency (RF) energy to study the distribution and behaviour of hydrogen protons in fat and water

RF energy is used to generate a second magnetic field, perpendicular to the static magnetic field of the machine. The result of this second magnetic field is to rotate or flip the protons away from the static magnetic

Once the RF field is switched off, the protons experience only the effects of the static magnetic field and flip back to their original position During this return to equilibrium, a process which is called relaxation, protons emit the RF energy which they had acquired

This energy is detected by the antenna in the MRI machine, digitised, amplified, and, finally, spatially encoded by the array processor The resulting images are displayed on the operators console and can be recorded

Comparisons MRI image CAT image thorax Compare bone and soft tissue density

Comparisons MRI image CAT image abdomen Compare bone and soft tissue density

Comparisons MRI image CAT image head Compare bone and soft tissue density