WEEK 1: MEDICAL IMAGING TECHNIQUES Flashcards
What are x-rays?
What is x-ray attenuation?
*High energy light
*How much absorbed
Name 3 imaging techniques that use x-rays
*Transmission radiographs
*Contrast examination
*Computed tomography (CT)
State factors that influence x ray attenuation?
Note: More x-ray absorption is shown by white surfaces, less absorption is shown by dark surfaces.
*Physical density: Atoms closer together, more atoms per unit tissue
*Object thickness; MORE TISSUE=MORE ELECTRONS
*Atomic number: MORE ELECTRONS PER ATOM
*Favorable electron energy states: ORAL AND IV contrast, designed to stop x-rays
How are transmission radiographs created?
Transmission radiographs are X-ray images that are created by passing X-rays through an object and capturing the X-rays that pass through the object on the other side.
It is a shadow that the body cast from ana x-ray light.
Outline 3 examples of transmission radiograph
*Chest x-ray
*Abdominal plain film
*Bone film
Describe the following radiographic projections:
*Frontal
*Lateral
*Oblique
*Odontoid
FRONTAL: From the back or front
*Antero-posterior
*Postero-anterior
NOTE: The first part is determined by the side where the x-ray beam is at
LATERAL
*From the side.
OBLIQUE
ODONTOID: Through the mouth
State the advantages of transmission radiographs.
*Lower cost
*Most available
*Easy to do basic interpretations
State the disadvantages of transmission radiographs.
*Ionizing radiation hence theoretical risk of causing cancer
*Difficult to do advanced interpretation
*Less precise evaluation of tissues
Name the two elements found in contrast.
Barium and iodine
How are contrast exams done?
The contrast is inserted via a catheter to the area of interest to be images and then x-rays are shone which will be absorbed by the contrast as it flows hence enhanced x-ray attenuation.
State exams of contrast examination
Usually used to image tubular structures
*AIRWAYS Bronchogram
*BOWELS esophagram
*Urinary system
*Vasculature: angiogram
*Biliary system
*Uterus: hysterosalpingogram
State the advantages and disadvantages of using contrast examination
ADVANTAGES
*low cost
*Easy to do basic interpretation
*Can examine tubular structures
DISADVATAGES
*Ionizing radiation
*Only does tubular structures
Describe how a computed tomography (CT) is done.
A computerized tomography (CT) scan combines a series of X-ray images taken from different angles around your body and uses computer processing to create cross-sectional images (slices) of the bones, blood vessels and soft tissues inside your body. CT scan images provide more-detailed information than plain X-rays do.
It is a grid of x-ray attenuation calculated by a computer.
Describe the CT presentations:
*Axial
*Coronal
*Sagittal
Axial : as if cutting a loaf
Coronal: like front CXR
Sagittal: like lateral CXR
State the advantages and disadvantages of CT.
ADVANTAGES
*Intermediate cost
*Easy to do basic interpretations
*Best general exam for all organs
DISADVANTAGES
*Ionizing radiation
Describe how ultrasound / Sonography is used to image.
*You emit sound wave with a transducer
*Listen for echo
*Emit sound wave with a transducer
*Listen for echo
*etc.
What produces an echo?
Difference in tissues.
What do the following measure?
*Time for echo to return
*Loudness of return
*Measure of depth
* Measure of difference in acoustic impedance
What is acoustic impedance?
The resistance to the propagation of ultrasound waves through tissues.
What is shadowing?
Reflection of sound at an interface.
What is echogenicity?
Echogenicity is the ability to bounce an echo, e.g. return the signal in ultrasound examinations.
Structures that have a lot of tissue are more echogenic.
Describe echogenicity of the following structures.
*Uterus
*Subcutaneous fat
*Bladder
*Intermediate echogenicity
*Very echogenic
*Anechoic
State the advantages and disadvantages of ultrasound.
ADVANTAGES
*Lowest cost
*Most available
*No ionizing radiation
DISADVANTAGES
*No standard planes making it difficult to interpret
*Does not image air so can’t image the lungs
*Poor tissue penetration of ultrasound making it difficult to evaluate deep tissues
Describe how an MRI is done?
uses a magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in your body.
