Methods of cross-sectional imaging

Question 1

What is sound?

Answer 1

Mechanical energy transmitted through a medium as a longitudinal wave

Question 2

What is ultrasound?

Answer 2

Sound at a frequency above the audible range (>20,000Hz)

Question 3

What frequencies do medical ultrasound machines use?

Answer 3

2-15 million Hz or 2-15MHz

Question 4

What is ultrasonography based on?

Answer 4

Pulse echo principle - by measuring the time taken for a pulse of sound to return to its source the distance to the reflecting structure producing the echo can be calculated

Question 5

What are the different types of ultrasound image?

Answer 5

M-mode - non-anatomic images used for measurements of cardiac chambers and valves B-mode - cross-sectional anatomical images used for most ultrasound examinations

Question 6

What do ultrasound images represent?

Answer 6

Echoes generated in tissue mainly arising from non-specific tissue elements including fat/glycogen, collagen, vascularity, crystailline material, water

Question 7

What is high frequency ultrasound used for?

Answer 7

Detailed examination of small or superficial structures

Question 8

What is low frequency ultrasound used for?

Answer 8

Less detailed examination of deeply situated organs

Question 9

What are linear transducers used for?

Answer 9

Flat body parts such as equine metacarpus

Question 10

What are curved transducers used for?

Answer 10

Intercostal spaces

Question 11

What are the similarities between CT and MRI?

Answer 11

Both rely on computers to process electronic signals which are reconstructed into 2D or 3D images Require expensive equipment with high installation and running costs Need accurate positioning a still patient = GA IV contrast medium can be used to generate better images

Question 12

How long does a CT/MRI take?

Answer 12

CT <10 minutes MRI 45 minutes

Question 13

What contrast media is used in CT?

Answer 13

Aqueous organic iodides

Question 14

What contrast media is used in MRI?

Answer 14

Paramagnetic agents such as gadolinium chelates

Question 15

What is CT?

Answer 15

Method for producing cross-sectional images that involves irradiating the subject using a high energy, fan shaped circulating x-ray beam and capturing transmitted photons in electronic detectors positioned in a ring around the patient

Question 16

What is MRI?

Answer 16

Method for producing cross-sectional images that involves placement of the subject in a region of high magnetic flux, applying periodic magnetic pulses to change the orientation of atomic nuclei within the subject and collecting the radio waves that are emitted when these nuclei relax

Question 17

What do grey shades reflect in CT?

Answer 17

Tissue attenuation similar to conventional radiography

Question 18

What do grey shades reflect in MRI?

Answer 18

Relaxation times of tissues which are influenced by a variety of physiochemical properties

Question 19

What are the applications of radiography, ultrasonography, CT and MRI?

Answer 19