Final Flashcards
At what frequency do US waves travel through soft tissue?
1540 m/s
What are the three important properties of US?
Wavelength, wave frequency, acoustic velocity
What are the 4 interactions of US with tissues?
Absorption, reflection, scatter, refraction
What is absorption?
The strongest interaction between US and ST
Strongly contribute to beam attenuation during propagation
Increases as US frequency increases
What is reflection?
It occurs at the surface of a medium
Allows of image reconstruction
What is scatter?
Occurs in all directions from particles whose dimensions are smaller then the US wavelength
Causes a loss of wave intensity out of the main direction of the US beam
What is refraction?
When the US beam bend when it enters a medium of different wave velocity at non-normal incidence
When the US beam travels from an area of low sound velocity to an area of high sound velocity, the beam will —-
bend away from normal
When the US beam travels from an area of high sound velocity to an area of low sound velocity, the beam will —
bend toward normal
What is continous US
An older style of US
When the transducer will continously send out US waves
What is continous US
An older style of US
When the transducer will continuously send out US waves and would need a receiver to receive the reflected waves
What is pulsed US?
A new style of US
Usually 3-5 cycles in a length
Allows the transducer to receive the waves back and form an image
What is the piezoelectric effect?
The process of the US waves being reflected and scattered back to the transducer, which then is converted in electrical signals to create an image
What is the transducer?
The most important component of the US system
Produces US pulses and receives US echoes
How strong is a curvilinear transducer and what is it used for?
4MHz
Used for abdomen, pelvis, obstetric applications
How strong is a linear transducer and what is it used for?
7MHz
Used for vascular applications and superficial structures
How strong is a transvaginal and transrectal transducer?
8MHz
What is lateral resolution?
How close two objects can be perpendicular to the axis of the beam and still be detected as two distinct entities
What controls lateral resolution?
Beam width and shifting the focus on the US machine
What is axial resolution?
The ability to separate structures parallel to the US beam
Based on wavelength
What are the requirements of an US machine?
Uninterrupted power supply, processes to transform the acquired data into an image, a means to display the image, a hard drive to record the examination
What are the limitations of US in general?
Highly operator dependent
Bone and air cause the US wave to reflected
As US waves interact they lose energy as heat, degrading image quality that can render a non-diagnostic image
What is A mode
Amplitude mode
What is A mode used for?
Ophthalmology and was used to determine mid-line in the brain
What is B mode?
Brightness mode
A mode pulse are converted into “brightness dots”
What is B mode used for?
Baby scan, brain scans, testes
What is M mode?
Motion mode
Shows how the structures intersected by a line (placed along the area of interest) move toward or away from the probe over time
What is M mode used for?
Heart rate
What is Fresnel zone?
Near field
What is Fraunhofer zone
Far field
What is the direct piezoelectric effect?
An applied pressure wave generating a voltage pulse that is used in the reception of echo pulses
What is the converse piezoelectric effect?
An applied voltage producing a pressure waves and is responsible for US transmission
What makes up a routine abdominal US examination?
Aorta, pancreas, liver, biliary system, kidneys and spleen
What are the complication involved with an urgent abdominal US?
No fasting - gallbladder wall appears thickened and mimic a pathology
How do you prepare the patient for an urgent abdominal US
Have the patient on an IV drip, analgesics and antibiotics if WCC is high
How do you prepare a diabetic patient for an abdominal US?
Plan the appointment around the patient’s schedule to facilitate fasting and the meal associated with insulin
What should a patient do to prepare for an abdo US if they take medication?
Depending on the medication, have the patient wait until after the examination to take it, or have them drink a small glass of water to wash it down
What do you do if the patient forgets to fast?
This is common with non-English speaking, elderly and patients with poor memory
Rebook the appointment
What are two causes of gastric stasis?
Ileus - where the peristaltic motion of the bowels cease due to neurogenic obstruction
Positional stasis - when the patient eats a meal directly prior to going to bed and rises shortly before the examination time
What are the clinical indications of an abdo US specific to the pancreas?
Painless jaundice, palpable central abdominal mass, raised serum amylase, pain consistent with pancreatitis
What are the clinical indications of an abdo US specific to the liver?
Abnormal liver function test, clinical enlarged liver, pain in RUQ, mets, apparent jaundice, f/u from other imaging modalities
What are the clinical indications of an abdo US specific to the biliary tree?
Investigation of jaundice, abdominal pain, ?gallstones, symptoms of acute cholecystitis
