Chapter 1: Introduction

CT Contrast Concepts and Variations

Preferred modality for Trauma cases: skull fractures and brain injury. Imaging compact bone Head trauma Ferromagnetic objects Imaging time Tolerance for patient motion Cost

Appendix Location

Right Lower Quadrant Right Inguinal Region

Urinary Bladder Location

Right Lower Quadrant Left Lower Quadrant Hypo-gastric Region

Liver Location

Right Upper Quadrant Left Upper Quadrant (Left Lobe) Right Hypochondriac Region Epigastric Region Left Hypochondriac Region Right Lumbar Region

Posterior (Dorsal)

The back of the body or body part.

Separation of Body Cavities

The diaphragm separates the Thoracic Cavity from the Abdominopelvic/Abdominal Cavity. No physical structure separates the Abdominal Cavity from the Pelvic Cavity.

Anterior (Ventral)

The front of the body or body part.

Asthenic

10% of population, generally have slight build, with long, narrow shallow thorax, which is wider more superiorly. (long and narrow thoracic cavity, short abdominal cavity)

Hyposthenic

35% of population, have a build somewhere between asthenic and sthenic. (long and narrow thoracic cavity, long and narrow abdominal cavity)

Abdominopelvic Quadrants

4 Quadrants (left to right): (RUQ) Right Upper Quadrant (LUQ) Left Upper Quadrant (RLQ) Right Lower Quadrant (LLQ) Left Lower Quadrant

Hypersthenic

5% of population, have a massive truncated build, with a short, broad, deep thorax. (broad, deep, and short thoracic cavity, large abdominal cavity)

Sthenic

50% of population, considered to be average with respect to height, weight, and torso length, with a moderately short, broad, and deep thorax. (short, broad, deep thorax; long abdominal cavity)

Abdominopelvic Regions

9 Regions (left to right): Right Hypochondriac Region Epigastric Region Left Hypochondriac Region Right Lumbar Region Umbilical Region Left Lumbar Region Right Inguinal Region Hypo-gastric Region Left Inguinal Region

CT Slices

A CT image is typically called a slice, as it corresponds to what the object being scanned would look like if it were sliced open along a plane. An even better analogy is a slice from a loaf of bread, because just as a slice of bread has a thickness, a CT slice corresponds to a certain thickness of the object being scanned.

Horizontal, Transverse, or Axial

A plane running crosswise through the body at right angles to the sagittal and coronal planes, dividing the body into superior and inferior parts.

Mid-sagittal (or Median)

A plane running vertically or longitudinally from front to back through the mid-line of the body, dividing the body equally into right and left parts.

Coronal (or Frontal)

A plane running vertically or longitudinally from right to left parallel to the mid-coronal or mid-axillary plane, dividing the body into anterior and posterior parts.

Mid-coronal (or Mid-axillary)

A plane running vertically or longitudinally from right to left, dividing the body into equal anterior and posterior parts.

Contrast Media

CT: Iodinated: Ionic, Non-Ionic Barium dilutions MRI: Gadolinium based: NSF

Safety Issues

CT: Radiation MRI: Increase in body temperature Implanted devices Claustrophobic patients Excessive noise level External ferromagnetic objects

Compare/Contrast: CT vs. MRI Length of Exam

CT: fewer than 5 minutes MRI: 30-40 minutes

Proximal

Closer to the point of attachment.

Sagittal

Commonly used to refer to a plane running vertically or longitudinally from front to back parallel to the mid-sagittal or median plane, dividing the body into right and left parts.

Distal

Farther from the point of attachment.

CT Principles

Gantry - tube Detectors as image receptors ADC - conversion of signal Volumetric multi-slice helical scanners Protocols Window width Window level

CT Gantry Tilt

Head Imaging, Gantry is tilted 15 degrees from the long axis of the body to minimize the interface artifacts in the posterior inferior portion of the cranium caused by the intense contrast differences between dense bone and soft tissue of the brain.

MRI Principles

Hydrogen atoms: Precess, Out of phase Magnet strength Radio-frequency pulsation PD/T1/T2 Weighting Imaging Time: Related problems, Solutions Protocols for pregnant women

MRI Contrast Concepts and Variations

Images obtained in any plane, including trans-axial, coronal, sagittal, and oblique. Involves no ionizing radiation. Excellent low-contrast resolution and superior ability to differentiate soft-tissue densities. Preferred modality for CNS pathology demonstration.

CT Advantages

Imaging compact bone Head trauma Ferromagnetic objects Imaging time Tolerance for patient motion Cost

MRI Advantages

Imaging planes No ionizing radiation Contrast resolution

Spleen Location

Left Upper Quadrant Epigastric Region Left Hypochondriac Region

Stomach Location

Left Upper Quadrant Epigastric Region Left Hypochondriac Region Umbilical Region

Production of MRI and CT Images

MRI utilizes magnetic field. MRI-can obtain in various planes, such as axial, coronal, sagittal, and oblique. MRI does utilize some post processing, but it is not utilized as much as it is in CT. CT utilizes x-ray tubes and detectors. CT-most often acquires images in an axial plane. CT utilizes post processing to obtain images in various planes, utilizing the initial data (Raw), images can be produced in almost any plane.

Compare/Contrast: Beam Hardening

MRI- no Beam Hardening Beam hardening artifacts appear as streaks and shadows adjacent to areas of high density such as the petrous bones, shoulders, and hips. The artifact occurs because the high density anatomy absorbs the lower energy photons while the higher energy photons pass through to the detectors which results in the beam becoming 'harder'.

MRI Strength

Measured in tesla (T): 1.5-T Magnet: Standard Magnet Strength 2-T Magnet: Decreased Image Quality 3-T Magnet: Improved Resolution; "phase artifacts"