WEEK 1: MEDICAL IMAGING TECHNIQUES

Question 1

What are x-rays?
What is x-ray attenuation?

Answer 1

*High energy light
*How much absorbed

Question 2

Name 3 imaging techniques that use x-rays

Answer 2

*Transmission radiographs
*Contrast examination
*Computed tomography (CT)

Question 3

State factors that influence x ray attenuation?

Note: More x-ray absorption is shown by white surfaces, less absorption is shown by dark surfaces.

Answer 3

*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

Question 4

How are transmission radiographs created?

Answer 4

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.

Question 5

Outline 3 examples of transmission radiograph

Answer 5

*Chest x-ray
*Abdominal plain film
*Bone film

Question 6

Describe the following radiographic projections:
*Frontal
*Lateral
*Oblique
*Odontoid

Answer 6

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

Question 7

State the advantages of transmission radiographs.

Answer 7

*Lower cost
*Most available
*Easy to do basic interpretations

Question 8

State the disadvantages of transmission radiographs.

Answer 8

*Ionizing radiation hence theoretical risk of causing cancer
*Difficult to do advanced interpretation
*Less precise evaluation of tissues

Question 9

Name the two elements found in contrast.

Answer 9

Barium and iodine

Question 10

How are contrast exams done?

Answer 10

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.

Question 11

State exams of contrast examination

Answer 11

Usually used to image tubular structures
*AIRWAYS Bronchogram
*BOWELS esophagram
*Urinary system
*Vasculature: angiogram
*Biliary system
*Uterus: hysterosalpingogram

Question 12

State the advantages and disadvantages of using contrast examination

Answer 12

ADVANTAGES
*low cost
*Easy to do basic interpretation
*Can examine tubular structures

DISADVATAGES
*Ionizing radiation
*Only does tubular structures

Question 13

Describe how a computed tomography (CT) is done.

Answer 13

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.

Question 14

Describe the CT presentations:
*Axial
*Coronal
*Sagittal

Answer 14

Axial : as if cutting a loaf
Coronal: like front CXR
Sagittal: like lateral CXR

Question 15

State the advantages and disadvantages of CT.

Answer 15

ADVANTAGES
*Intermediate cost
*Easy to do basic interpretations
*Best general exam for all organs

DISADVANTAGES
*Ionizing radiation

Question 16

Describe how ultrasound / Sonography is used to image.

Answer 16

*You emit sound wave with a transducer
*Listen for echo
*Emit sound wave with a transducer
*Listen for echo
*etc.

Question 17

What produces an echo?

Answer 17

Difference in tissues.

Question 18

What do the following measure?
*Time for echo to return
*Loudness of return

Answer 18

*Measure of depth
* Measure of difference in acoustic impedance

Question 19

What is acoustic impedance?

Answer 19

The resistance to the propagation of ultrasound waves through tissues.

Question 20

What is shadowing?

Answer 20

Reflection of sound at an interface.

Question 21

What is echogenicity?

Answer 21

Echogenicity is the ability to bounce an echo, e.g. return the signal in ultrasound examinations.

Question 22

Structures that have a lot of tissue are more echogenic.
Describe echogenicity of the following structures.

*Uterus
*Subcutaneous fat
*Bladder

Answer 22

*Intermediate echogenicity
*Very echogenic
*Anechoic

Question 23

State the advantages and disadvantages of ultrasound.

Answer 23

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

Question 24

Describe how an MRI is done?

Answer 24

uses a magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in your body.

Question 25

State the advantages and disadvantages of an MRI

Answer 25

ADVANTAGES
*No ionization
*Uses standard planes for easy to interpret
*Best tissue contras
*Non-invasive

DISADVANTAGES
*High cost
*Limited availability
*Complicated physics so can be difficult to interpret
*Images air poorly so can’t see the lungs

Question 26

Describe how NUCLEAR MEDICINE is used to image.

Answer 26

*A radioactive pharmaceutical is injected and deposited into tissues
*A gamma camera is then used to measure radiation and make images.

Question 27

State 2 agents for nuclear medicine

Answer 27

*Radioactive substance
*Biologically active substance

Question 28

State the advantages and disadvantages of nuclear medicine.

Answer 28

ADVANTAGES
*Can image physiology

DISADVANTAGES
*Ionizing radiation
*High cost
*Limited availability in Botswana
*Difficult to manufacture pharmaceuticals
*Low spatial resolution

Question 29

Outline structures which can be imaged by nuclear medicine.

Answer 29

*Bone remodeling (bone scan)
*Thyroid function (thyroid scan)
*Renal function (nuclear renograms)