Biopshysics Flashcards
(23 cards)
What are the 3 different ways US can interact with tissues?
Reflection
Scatter
Absorption
What is the tissue property that determines how much a US is reflected?
Acoustic Impedence (Z) The greater the difference in Z between the 2 tissues then the more reflection you get
How do we calculate acoustic impedence (Z)
Z = p x c
Z = Acoustic impedence p = density of the tissue c = velocity of the US in that particular tissue
When do you get US wave scattering. And what is the term for this??
When the US interacts with a structure which has small dimensions/or has similar dimensions to the wavelength of the US wave.
Knwon as Rayleigh scatterin = Waves are scattered in all directions 360degrees
What is ultrasound absorption
When it is absorbed and can turn into internal molecular energy or heat.
What is real time B-MODE (brightness mode) scanning?
This is when US beams are swept across the field to produce one whole image.
What are the limitations of real time B mode scanning?
Inadequate spatial resolution Inadequate penetration Poor image quality Low frame ate Compromised field of view Low line density
What is the doppler effect?
The differenc ein the frequency of the sound between the returning echo and the transmitted US wave. This can be used to assess blood flow
How does doppler work?
Doppler scanners themselves just need to use continuous wave ultrasound to see the direction and speed of flow. Here they can give colour flow images, where red generally means towards the probe, and blue is aware from the probe. ALso the brighter coloured hues mean high velocity (arteries), while darker means lower veloicty (veins)
You need to combine the above doppler scanner with a B mode real time grey scale in order to actually see some images however. Just the doppler wouldnt show any structures.
What are the heating dangers of US
The absorption of the US waves can cause increased temp in tissues. WIth certain structures like bone taking the biggest temp rises. Need to be careful in young foetuses with longer diagnostic scans to consider this.
May also cause damage to small embryos.
What are the 3 thermal indexes for heating with USS
There are 3 because different tissues heat up at different rates
1) TIS = Thermal index in soft tissues
2) TIB = Thermal index in Bone
3) TIC = Thermal index in the cranium
Note that each type of USS has values for these and the operator should be aware of them.
We recommend monitoring TIS during scans carried out in the first 8 weeks following conception, and thereafter.
What is cavitation with US? What is the name of the index to measure it.
US can lyse and damage cells in suspension. It does this with gas filled cavities, when exposed to US they can oscillate or collapse under the US and damage cell membranes or produce highly reactive free radicals.
There is also an index to account for possibility of bioeffects from these mechanical effects.
KNOWN as the mechanical index.
BUT = This has not been shown to cause damage in humans, except when microbubble contrast agent is present.
How does DEXA or dual energy X ray absorptiometry work?
Sends out 2 beams of low dose X ray with differing energy levels through the bones.
One of these beams just penetrates through the soft tissues and is subtracted. These beams can then be used to calculate the BMD.
Remember T score less between -1 and -2.5 is osteopaenia, and below -2.5 is osteoporosis.
T score Vs Z score
T score is using a young adult
Z score is comparing ages as well so comparing to other people the patients age.
How does MRI work briefly
A radiofrequency pulse is emitted which disrupts the alignment of protons.
These protons then drift back into alignment, and doing so release a detectable radiofrequency signal. This is what is detected.
How can the various waveforms of electrical current change the effect of the instrument
1) Continuous current = Causes cutting as it vaporises through cells
2) Higher voltage but intermittent current = Causes a coagulation effect.
3) Combination of bursts of low voltage (cutting) and high voltage (coagulation) currents = This causes cutting with coagulation effects.
What is desiccation vs fulguration
Desiccation = You’ve seen a lot its extreme drying where tissues are coagulated by high temps using elec.
Fulguration = Where you dont even touch the probe to the skin but can coagulate a very large area.
When are CO2 lasers used
CO2 gas lasers allow precise tissue cutting and dissection with minimal lateral damage
Can be used in O and G for removal of endometriotic implants, especially near the ureters.
When are solid state lasers used
Example = Neodymium-doped yttrium aluminium garnet (nd:YAG) produces high energy beam in infrared spectrum
Can cause cutting and haemostatic effects, and also vaporise tissues.
This beam can be transmitted down a fibre and it can penetrate deep into tissues which makes it useful in hysteroscopic procedures.
What are the types of external beam radiotherapy
CRT = 3D conformal radiotherapy. This uses variable number of beams each targeting the tumour.
IMRT = intensity-modulated radiation therapy is the next gen of 3D CRT. In this case the intensity of the beams can also be modulated which llows for greater control even within the distribution zone.
What are the types of internal beam radiotherapy
Sealed source radiotherapy and unsealed.
Brachytherapy can be used to treat various gynae cancers including vaginal, cervical, ovarian and uterine.
Name 4 of the acute adverse events of radiotherapy
1) Damage to epithelial surfaces such as skin, oral and bowel mucosa
2) Oedema and swelling of soft tissue, can be ameliorated with steroids
3) infertility caused by damage to gonads
4) generalised fatigue
Name 5 medium and long term effects of radiotherapy
1) fibrosis and diffuse scarring
2) hair loss
3) Dryness due to damage of ducts including salivary, tear, or vaginal dryness
4) fatigue and lethargy
5) cancer secondary to irradiation
6) death
