CSD Abdominal CT Scan Workshop

Abdominal CT Scan Workshop

• This workshop covers abdominal CT scans, a radiological imaging technique.
• The workshop was led by Dr. Andres Aranda, MD, a nephrologist.
• The workshop's block is 9.

Objectives

• Review basic CT scan principles.
• Recall CT scan advantages over X-rays.
• Understand different views in abdominal CT scans.
• Review non-contrast vs. contrast CT scan advantages and disadvantages.
• Recall structures assessed in abdominal CT scans.
• Follow a checklist for abdominal CT scan assessment.

CAT Scan Basics

• CT scans use X-rays rotated around a patient.
• Computer processing creates cross-sectional images.
• CAT scan (Computer Axial Tomography) was initial name used.

History

• CT scans (computed tomography): a radiological imaging technique.
• Developed by Allan MacLeod Cornmack & Godfrey Hounsfield.
• Awarded the Nobel Prize in Physiology or Medicine (1979).
• First installed 1974.
• X-ray beams rapidly rotate around the subject to create images.

CT Scan

• Essentially an X-ray study, producing cross-sectional images of the body.
• Detailed examination of bones, organs, blood vessels and tissues is possible.
• Low-dose CT scans (10 mSv; 10 times that of a standard abdominal X-ray).
• CT scans involve ionizing radiation that can cause biological harm.
• Has a higher radiation dose than conventional X-rays (50 to 1000 times).
• Account for a considerable portion of radiation exposure to the population.
• Approximately 50% of medical radiation exposure is from CT scans.

X-Ray vs. CT Scan

• X-rays are limited in detail, primarily highlighting bone density.
• CT scans offer high-resolution imaging, evaluating soft tissues, organs, and bones comprehensively.

Indications

• Utilized in inpatient and outpatient settings for serious illnesses.
• Diagnosing or narrowing differential diagnoses.
• Cancer screening, staging, and follow-up.
• Performing biopsies and assisting surgical procedures.

Imaging

• X-ray beams create images based on tissue density.
• Tissue density is measured in Hounsfield Units (HUs).
• HUs indicate how much X-ray energy a tissue absorbs.

Hounsfield Units (HU)

• Attenuation (reduction of X-ray beam intensity) is directly related to the Hounsfield units (HU).
• HU values are quantitative measures of tissue density in CT imaging.
• Hyperdense tissues have positive HU values (e.g., bone).
• Hypodense tissues have negative values (e.g., air).
• Isodense tissues have a HU of 0 (e.g., water).

Attenuation

• Attenuation is the reduction of X-ray beam intensity as it passes through tissues.
• Tissues attenuate X-rays differently depending on their density.
• Dense structures (e.g., bones) attenuate more X-rays and appear brighter.
• Less dense structures (e.g., air, soft tissue) attenuate fewer X-rays, appearing darker.

Orientation and Views

• Axial scans (cross-sectional images) are the most common view.
• Other views (sagittal or coronal) can be used as needed.
• Axial scans imagine the subject from their feet, with the left side of subject appearing on the right side of the image.

Orientation/Technique

• Describes the positioning of the patient during a CT scan.
• Shows X-ray generator-detector positioning in relation to the patient.

Views in CT Scan

• Axial, coronal and sagittal views are produced to evaluate the subject.
• These are used to examine the: heart, liver, major vessels, aorta.

Non-Contrast vs. Contrast Abdominal CT Scan

• Non-contrast: Imaging without contrast agents.
• Utility: Assessing baseline anatomy, identifying calcifications/fractures, and minimizing contrast risks.
• Contrast: Utilizes contrast agents to enhance visibility.
• Utility: Improving visualization of the GI tract, blood vessels, and other tissues. Identifying and characterizing lesions comprehensively.

Abdominal Anatomy on Computed Tomography

• Images in this modality are used to visualize the anatomy.

Sources

• Includes links to resources for further study.

Checklist for Abdominal CT Scan Structural Assessment

• Abdominal wall
• Bones: Ribs, vertebral column, hip bones
• Peritoneal cavity
• Solid organs (e.g. liver, spleen, pancreas, suprarenal glands, kidneys)
• Hollow organs (e.g. stomach, small intestine, duodenum, jejunum, ileum, cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum).
• Blood Vessels (e.g. Aorta, celiac trunk, SMA, IMA, IVC, splenic vein, SMV, IMV).