Methods - cross sectional image Flashcards
How are ultrasound images formed?
- based on 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
- an ultrasound transduce emits sound 99.9% of the time
- a typical ultrasound pulse lasts a few us
2 types of ultrasound image
- M-mode: non-anatomic images used for measurements of cardiac chambers, valves
- B-mode: cross-sectional anatomical images used for most ultrasound exams
What do ultrasound images represent?
represent echoes (backscatter) generated in tissue)
- mainly arises from non-specific tissue elements that occur in most tissues including:
- fat or glycogen
- collagen
- vascularity
- crystalline material
- water/ oedema
What frequencies are used for ultrasound?
- sound at a frequency above the audible range i.e. >20,000 Hz
- medical diagnostic ultrasound machines use frequencies in the range 2-15 million Hz or 2-15 MHz
Which backscatter is hyperechoic?
- fat or glycogen
- collagen
- vascularity
- crystalline material
Which backscatter is hypOechoic?
- water/oedema
T/F: there is no simple correlation b/w the appearance of a lesion in an ultrasound image and its histology
TRUEE: pathological entities such as inflammation, neoplasia, hypertrophy share many gross features and do not produce any characterisstic effects on the ultrasound beam
What is a high frequency trasnducer used for?
- detailed exam of small or superficial strucutre
- 7.5MHz
Use - low frequency transducer
- less detailed exam of deeply situated organs
- 3.5MHz
Use - wide, flat (‘linear’) transducers
- flat body parts
- eg. equine metacarpus
Use - narrow, curved transducer (e.g. ‘sector transducer’)
- intercostal space
Similarities- CT and MRI
- both rely on computers to process electronic signals which are reconstructed into 2D or 3D matrices using sophisticated mathematical algorithms
- expensive equipment
- high installation and running costs
- hence limited availability
- accurate positioning, still patient usually requires GA
Typical image time - CT and MRI
- CT
How can the visibility of lesions that damage the BBB be increased?
- IV injection of contrast medium
- CT: aqueous organic iodides
- MRI: paramagnetic agents (gadolinum chelates)
Principle of CT
= computed x-ray tomography
- priduces cross-sectional images that involves irradiating the subject using high energy, fan-shaped circulating x-ray beam and capturing transmitted photons in electronic detectors positioned in a ring around the patient
