Xray and CT

Why Study Imaging?

1.) A more comprehensive evaluation is obtained

2.) The information the physical therapy clinician seeks is often of a different nature from the information the physician seeks and even of a different nature from what may be described in the radiologist’s report.

* Collaboration requires an understanding of what each party has to offer.

Historical Perspective: 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.

1910-20

Military use of X-rays during WWI to screen for TB, Fluoroscopy to locate bullets, and screen for emergency surgeries, and spin off of sonar technology-diagnostic US

1930-40

Nuclear medicine with the development of the cyclotron (particle acclerator) by Ernest Lawrence, Curie-Frédéric for synthesis of artifical radioactivity, little consideration for the adverse effects of radiation exposure until the atomic bomb was dropped in 1945.

1950-60

The ALARA (as low as reasonably achievable) remains the recommendation of effective dose limits for occupational, diagnostic, therapeutic exposure, and clinical application for all the advanced imaging modalities developed. First image intensifier and TV viewing in 1955, and first automatic x-ray processing system was marketed by Kodak in 1956.

1970-80

Computed tomography (CT) merged x-ray technology with the computer, and cross-sectional images were now possible, and in 1978 the first analog waveform image was converted to a digital image and accelerated a subspecialty of radiology known as interventional and invasive radiology.

Magnetic resonance imaging (MRI), was approved for clinical use in 1984, so now one could view the CNS and all tissues in the body.

1990-21st century

Conversion of film-based imaging to digital imaging with the charged-coupled device (CCDs) in the 1990’s

Radiograph:

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

• A conventional radiograph is one made without contrast enhancement or other equipment modifications.

• The conventional radiograph is generally the first diagnostic study to be done following the clinical examination.

• Conventional radiographs are the most efficient means to demonstrate bone and joint abnormalities.

What are X-rays?

A form of ionizing electromagnetic radiation, similar to visible light but of shorter wavelength (10-8 -10-11 m).

How are X-rays produced?

Requires 3 things:

• Source of electrons

• Force to move them rapidly

• Something to stop them rapidly

X-ray tube and electrical source

How do they interact with the patient? - xray

• The collimator controls the size and shape of the x-ray field

• The primary beam passes through the patient and is attenuated (scattering and absorption)

How is the image made?

• The x-ray beam is attenuated in different amount, depending on the density of the tissue it has passed through.

• The remnant beam is intercepted by an interpretation device called an image receptor and produces a latent image which is converted into a visible image.

Understanding the Image:

• The image is the result of the interaction of x-rays with body tissues

• The identification of anatomy by different shades of gray is dependent on each tissue and it’s radiodensity.

• Radiodensity depends on:

  • Composition (atomic number and volume density)

  • Thickness

Anatomy in Four Shades of Gray:

• Air- Black

• Fat- Gray-Black

• Water- Gray (all soft tissues and fluids such as in nerves, blood, muscle, cartilage, tendons and ligaments)

• Bone- White

Radiodensity Based on Thickness:

The thicker an object is the more radiodensity it possess relative to thinner object made of the same substance.

How Many Dimensions Can You See?

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

Routine Radiograph:

• The routine radiograph examination evaluates a body segment via a standard selection of position and projections chosen to provide the greatest visualization with minimal radiation exposure.

• AP, Lateral, and Oblique projections compose most routine series

The Image Quality Factors of the Radiograph

• Density

• Contrast

• Detail

• Distortion

The Imaging Chain:

• Humans play a critical role in the imaging system by their interpretation of the image and by their correlation of clinical findings with imaging information.

• The clinicians responsibility is to recognize always that if the results of any imaging study do not fit the physical findings, further clinical evaluation and diagnostic investigation are warranted

Radiographic Evaluation & Search Pattern:

Radiographic image interpretation requires:

• Foundations in imaging technology

• Dimensional perception and knowledge of anatomy

• Organized search pattern

• Characteristic patterns of pathology

Wolff’s Law:

• Remodeling of bone, which occurs continuously throughout life, is directly related to function.

• Bone is deposited in the sites subjected to stress and resorbed in sites deprived of stress.

Alignment:

• General Skeletal Archietecture

  • Gross size, appearance and number of bones

• General Contour of Bone

  • Normal shape and contour

• Alignment of Bones to adjacent Bones

  • Normal joint articulation and spatial relationship

Bone Density:

• General Bone Density

  • Contrast of soft tissue and bone (shades of gray),

  • Contrast between cortical and cancellous bone

• Textural Abnormalities

  • Normal trabecular architecture

• Long Bone Density Changes

  • Sclerosis at areas of increased stress such as weight-bearing surfaces or site of ligamentous, muscular, or tendon attachment

Cartilage Spaces:

• Joint Space Width

  • Well preserved joint spaces imply normal cartilage or disk thickness

• Subchondral Bone

  • Smooth surface

• Epiphyseal plates

  • Normal size relative to epiphysis and skeletal age

Soft Tissues:

Muscles, Fat pads and lines, Joint capsules, Periosteum, Miscellaneous

The Radiographic Search Pattern (ABCs):

• alignment

• bone density

• cartilage spaces

• soft tissues

Muscle

Look for wasting, swelling, edema, hemorrhage, or tumor

Fat Pads & Fat Lines

Displacement is usually due to swelling

Joint Capsule

Distended due to swelling or effusion

Periosteum

Normally rather indistinct, can have periosteal reaction

Miscellaneous

Gas, calcification, foreign bodies

General Bone Density

Contrast of soft tissue and bone (shades of gray),

Contrast between cortical and cancellous bone

Long Bone Density Changes

Sclerosis at areas of increased stress such as weight-bearing surfaces or site of ligamentous, muscular, or tendon attachment

Advantages of Radiography:

• 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

Disadvantages of Radiography:

• 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 it’s 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.

Variations of Radiographs:

• Fluoroscopy

• Arthrography

• Myelography

• Arteriography & Angiography

• Contrast-enhanced

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.

• Is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers.

Contrast-Enhanced:

• Radiolucent = “Air”, called a negative contrast.

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

• Inject or ingest a contrast medium.

Computed Tomography (CT):

• 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 scanning became widely available in the 1980’s and has improved greatly in the past 40 years as a result of the advances in computer science.

• 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 a CT scan made? - A CT scanner has three components:

• The gantry- what the patient slides into, it is the frame that contains x-ray tube, the detectors, and the data acquisition system.

• The operator console- where the CT technician controls the scanning process to select slice thickness, and reconstruction algorithms.

• The computer- which converts the radiodensities obtained from the gantry detectors into digital signals and finally into a matrix of pixels.

How is a CT scan made?

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

• The shade of gray is expressed as a Hounsfield unit (HU).

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

• The computer can differentiate thousands of levels of radiodensity, or shades of gray.

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

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.

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

Contraindications of CT:

• 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

Summary of CT:

• Thinner slices and smaller pixels improve the spatial resolution.

• Thicker slices and larger pixels improve contrast resolution.

• Modern neuroimaging consists of CT, MRI, and variants of the two employed to depict metabolic activity and follow patterns familiar with MSK imaging, which are based on cell density, fat, and fluid content.

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