MOD 1 obj - CT, X RAY

Who invented the ct scan?

• CT was invented in 1972, by Godfrey Hounsfield and utilized mathematical formulas developed by Alan Cormack to reconstruct images from digital signals.

• They won the Nobel Prize in Physiology/Medicine in 1979 for the development of computer- assisted tomography.

• CT merges x-ray technology with advanced computer post-processing to provide detailed digital cross-sectional images of the body relatively free from superimposition of the different tissues.

How is CT imaging different than X-ray?

It can create images in all 3 orthogonal planes

Thousands of shades of gray, a technical “window” is set to display a range of radiodensities based on the tissue being examined

How is CT imaging the same as X-ray?

• Each pixel is assigned a shade of gray to correlate with the radiodensity of the cubic volume of the tissue it represents.

• A HU is a measurement of tissue radiodensity. Water is arbitrarily set at 0 HU.

• Basically though, the major tissues are still represented as “four shades”.

What type of resolution is improved with thinner slices and small pixels?

• Thinner slices and smaller pixels improve the “spatial resolution”

• Thin slices require greater radiation, increased number of slices, and total duration of imaging time.

What tissue is best represented in a CT scan?

It is a highly detailed depiction of normal anatomy and pathological processes in cross section especially for bone and joint space.

What is the imaging modality of choice in the acute setting with trauma?

CT is the modality of choice for neuroimaging in acute settings and in cases of trauma

What are the three characteristics the CT scans high-light in the human body?

Cell Density

Fat

Fluid Content

What are the advantages of CT

• It is a highly detailed depiction of normal anatomy and pathological processes in cross section.

• It is less time consuming than MRI or US.

• Allows for accurate measurements of osseous alignment in any plane.

• It is usually less expensive than MRI

• It is less problematic than MRI for patients with claustrophobia.

what are the disadvantages of CT?

• It is a high radiation exposure relative to most conventional radiographic exams

• Has less soft tissue contrast than MRI

• Is possible to have static versus dynamic examinations with diagnostic ultrasound

Are there any contraindications for CT and why?

• CT imaging has no absolute contraindications. The relative contraindications are related to the radiation dosage.

• For CT with contrast, two contraindications are:

  • Contrast-induced nephropathy

  • Allergy to iodinated contrast

Who discovered X-rays and was awarded the Nobel Prize in Physics in 1901?

• Discovery of x-rays by Wilhelm Conrad Röntgen in 1895.

  • Electromagnetic radiation in the wavelength range of X-rays.

  • Awarded the 1st Nobel Prize in Physics in 1901.

• Discovery of radioactive elements by Marie Curie in 1898.

  • The Theory of radioactivity- isolated radioactive isotopes using polonium and radium

  • First women to receive the Nobel Prize in 1903 in Physics, and then again, she received the Nobel Prize in Chemistry in 1911.

Define radiograph?

A recorded image of an anatomic part acquired by the passage of x-ray through the body.

What is the first imaging study done following a clinical examination?

Conventional radiograph

What is the most efficient image to look at bone and joint abnormalities?

Conventional radiograph

What are the three things required to produce an X-ray image?

• Source of Electrons

• Force to move them rapidly

• Something to stop them rapidly

The shades of gray on a radiograph are determined by tissue radiodensity, what are the two determinants of radiodensity?

Composition (atomic number and volume density)

Thickness

What are the four tissue radiodensities in the human body?

• AIR

• FAT

• WATER- All soft tissue and fluids (blood, muscles, nerves, cartilage, tendon and ligaments)

• BONE

What is the relationship between the absorption of x-rays (amount of the object radiodensity) and the amount of blackening on the x-ray (radiographic density)?

INVERSE

RADIOPAQUE - “Bone”

RADIOLUCENT – “Air”

What is meant by the term, “one view is no view?

At least two images, as close to 90 degrees to each other as possible, are required to view all three dimensions of a structure.

What are the four factors that determine the quality of a radiograph?

• PHOTOGRAPHIC PROPERTIES

  • Density

  • Contrast

• GEOMETRIC PROPERTIES

  • Details

  • Distortion

What ar ethe ABCs for X Ray

• alignment

• bone density

• cartilage spaces

• soft tissues

Alignment:

General Skeletal Architecture

General Contour of Bone

Alignment of Bones to adjacent Bones

Bone Density:

General Bone Density

Textural abnormalities

Local Bone Density Changes

Cartilage Spaces:

Joint Space Width

Subchondral Bone

Epiphyseal Plates

Soft Tissues:

Muscles, Fat pads and lines, Joint capsules,

Periosteum, Miscellaneous

X Ray advantages

• Is Fast

• Is Inexpensive

• Provides a relatively low radiation dose

• Provides an excellent definition of Bone

• Screens for significant portion of pathologies

• Is valuable in directing which imaging study to use next if more information is needed to define a condition.

X Ray Disadvantage

• Radiographs can show only significant changes in bone density. Therefore, if a disease is slow to alter density, the evidence of the disease may not become visible until in its advanced stages.

  • Osteoporosis

  • Avascular Necrosis

  • Stress Fractures

• Radiographs are 2-dimensional, and the 3rd dimension is limited by superimposition of tissues.

• Soft tissue not well-defined.

Fluoroscopy

• A real-time or dynamic or continuous radiographic exam used to guide interventional procedures

• Analogy:

  • Radiograph = Photograph

  • Fluoroscopy = Movie

Arthrography

An image made of a joint after it has been injected with a contrast.

There are conventional arthrography and MR and CT arthrography

Myelography

An image made with an injection of contrast medium into the subarachnoid space to examine the spinal cord and nerve roots

There are conventional myelography and CT myelography which is the most common used today.

Arteriography & Angiography

Is an x-ray examination of the arteries, or blood vessels. To make the arteries visible on x-ray, a type of dye called “contrast” is injected.

Contrast-enhanced (inject or ingest a contrast medium)

Radiolucent = “Air”, called a negative contrast.

Radiopaque = “Barium sulfate or iodine”, called a positive contrast.