Biophysics Flashcards
In the ECG what represents
I) Atiral repolarisation
II) Ventricular repolarisation
i) Not as during ventricular polarisation (QRS)
II) T wave
The large squares on an ECG (measuring 5mm) represent what time period
1mm wide small square
- 2seconds
0. 04seconds
Which leads are the inferior leads
III, aVF, II
Which leads are the anterior leads
V1-v4
Which leads are the lateral leads
aVL, 1, V5&V6
Which leads are the right atrium and left ventricle leads
aVr and V1
What is the normal QT interval
0.3-0.43 seconds (0.3-0.45 in women) - time for depolarisation and repolarisation of the ventricles
Sound waves above what hertz are termed ultrasound?
20kHz
Most medical ultrasound is the low MHz range.
In ultrasound how is the pressure wave created?
Piezoelectric crystal within a transducer - the piezoelectric crystal converts electrical energy into mechanical energy & vica versa (with high voltage current the crystal oscillates)
What is the pulse repetition frequency?
indicates the number of ultrasound pulses emitted by the transducer over a designated period of time.
What is the acoustic impedance
the tissue property that determines the degree of reflection
the greater the difference of acoustic impedance between 2 tissues the greater the degree of reflection.
What it the equation to calculate acoustic impedance
acoustic appendance = density x velocity of ultrasound
When does scatter occur?
When the ultrasound interacts with a structure with a similar dimensions (or smaller) then the length of the ultrasound wavelength e.g. blood cells and parenchyma
What direction is the ultrasound scatter in? How does it appear
360 degree
speckled appearance
What happens to the intensity of scatter as the frequency of ultrasound is increased
scatter increases very quickly putting an upper limit on ultrasound
What is absorption in ultrasound? For safety what is the upper limit of ultraounds
Conversion of mechanical every into heat or internal molecular energy producing heat.
Absorption increases with high frequencies - upper limit of 20MHz
Typically how many beams produce one image
200
What is the function of power in ultrasouns
The electric voltage used to generate the ultrasound pulses
What is the gain
The recieved signal is amplified to useful levels
What is attenuation?
How does this change with different frequencies and how does this impact clinical practice?
The amplitude and intensity of ultrasound waves decrease as they travel through tissue, a phenomenon known as attenuation. Given a fixed propagation distance, attenuation affects high frequency ultrasound waves to a greater degree than lower frequency waves. This dictates the use of lower frequency transducers for deeper areas of interest, albeit at the expense of resolution.
What is time gain compensation?
Amplify (increased gain) for deeper depths to adjust for attenuation
What are the limitations of real time B-mode scanning
inadequate spatial resolution inadequate penetration poor image quality low frame set compromised field of view low line density
What is spatial resolution?
Minimum distance between two reflectors or scattering surfaces to be able to distinguish between 2 signals
What are the two main components of spatial resolution and how are they impacted?
Axial resolution: determined by pulse length, shorter at high frequency (higher frequency is better axial resolution)
Lateral resolution: determined by beam width
What affects penetration os USS
Absorbtion and scatter - both increased with high frequency. Lower frequency for deeper penetraion but at cost of resolutino n
What information can doppler ultrasound tell us?
The speed at which a target is moving
direction of movemen
Direction of movement
Calculated using principles of doppler frequency shift
What is the colour coding system on dopplers
Red: towards transducer
Blue: away from transducer
Dark hues: low level velocity
Light hues: high level velocity
What measurement is used to account for possibility of bio effects of from heating.
Thermal index
TI soft tissues/bone/cranium
The mechanical index is to minimised the risk of…?
Cavitation - gas filled cavities can oscilllate or collapse under pressure of USS
What is the wavelength of XRAY?
How does this compare to ultraviolet and gamma rays?
10-0.01nm
Longer than gamma, shorter than ultra violet
How are XRAY images produced?
Accelerating electrons made to collide with a metal target. Body creates a shadow, as XRAYs are attenuated by dense tissue, dense appears white.
What is real-time X-ray procedures?
Radioopaque contrast agents are used to highlight organs or vessels depending on where they are injected.
What is hysterosalpingography
When is it performed
To assess tubal patency
performed 1st 10 days of menstrual pregnancy to avoid exposure in early pregnancy
Benefits of HSG
minimally invasive, rare complications, quick, valuable information on uterine cavity and potency of tubes
Disadvantages HSG
Radiation exposure 1mSv (4 months background radiation) - small risk of cancer
Risk flare of undiagnosed chronic pelvic pain. Exposure of unsespectant pregnancy
In electrosurgery why does low frequency current cause neuromuscular stimulation whilst high frequency does not?
At low frequency the cyclic polarisation/depolrisation allows transmembrane exchange of ions →neuromuscular stimulation
High frequency so fast ions do not have time instead collision of intracellular ions/materials producing heat
Do grounded (meaning current returns back to the unit via earth) or isolated systems risk burning the patient if the electrode is faulty or poorly applied?
Grounded
Difference between monopolar and bipolar?
Monopolar: One electrode in operators hand and return electrode is attached to the patient - the return electrode is attached tot eh diathermy machine.
Bipolar: Current flows between forceps - manymachines have a anticoagulation function where the machine sense optium degree of anticoagulation - no cutting function
What waveform is used for a cutting current?
Continous unmodulated with relatively low voltage, use tip of the electrode → creates high temp which vaproises the cells.
What waveform is used for coagulation?
High voltage applied intermittently, modulated to a duty cycle of about 6% → tissue can cool between heating bursts, no vaporisation
What is dessication?
Extreme drying, where by caogulation happens but at a high heat 70-100, requires contact with the active electrode & tissue, usually achieve on cutting mode 100% duty cycle - forms a coagulum
What is fulguration?
High powered current is used to produce sparks - not touching tissue, produces deeper coagulation than soft coagulation
What is direct coupling ?
Electrode is activated in close proximity or direct contact with another conductive instrument within the body
What is capacitive coupling?
Current between o conductors that are separated by an insulator
Safe electrosurgery practices
Check instruments insulation before surgery
Lowest power and voltage for desired effect
Active electrode only when needed
Never active the electrode when close or in contact ieth metal or conductive object
In endoscopic surgery, what does laser stand for?
Light amplification by stimulated emission of radiation.
What does the laser device emit?
Light photos (electromagnetic radiation) - a process called stimulated emission to vaporise, dissect and coagulate
Why is laser associated with less post op pain? Other benefit
Laser beams seal nerve endings, also natural sterilisation as they evaporate bacteria, viruses and fungi
What are the main types of laser devices?
CO2 gas
Argon ions
Solid-state lasers
How do CO2 gas laser works
What is a good use for this in gynaecology
Absorbed to high degree by soft tissues containing water - enables precise cutting/dissection with miinmal lateral damage
- Removal of endometriosis, especially near ureters
Disadvantage of CO2 laser
Expensive
Difficult to clean
Invisable to human eye - second laser needed
Depth is limited, unsuitable for most laproscopic sugery
How are solid lasers commonly made?
‘doping; a crystalstalline solid host with ions that provide the require energy state e.g. Nd:YAG → deeply penetrating
The beam passes through KTP potassium titanic phosphate for more disired effect → penetrate 1-2mm, vaporise cut & coagulated
The amount of radiation used in radiotherapy is called?
How does work?
Gray (Gy)
Damages cellular DNA - caused by photons, electrons, proteins, neutrons or ions
When radiationg works by indirect actions what is happening
H20 is ionised generating free radical H+ and OH- that damage DNA
What is the effect of tissue hypoxia on the effects of radiation?
Increases resistance
Why are portions (positive charged particles) prefered to photons (soft X-RAY)
Release energy at point of impact, rapid fall off, adverse effects are minimised
What are the main tyoes of external radiotherapy
Linear accelerator - 2D beans from 1-4 directions
Conformal radiotherapy CRT - 3D, multiple beams shaped to fit profile or target
Intensity modulated radiation therapy (IMRT) - intensity of each beam can be modulated
Main limitations of external beam radiotherapy?
Unable to indenitfy microscopic disease
difficulty immobilising person/tumour
tumour shrinkage with Tx
What are the 2 main types of internal beam therapy?
Sealed source radiotherapy and non-sealed radiotherapy
What is the main type of sealed course radiotherapy, benefits?
Brachytherapy, sealed radioactive material is placed into or next to tumour.
Works over short distances, passing through less health tissue, lower energy radiotherapy.
What is unsealed source radiotherapy - give an example
Radioisotope is delivered by injection e.g. Iodine 131 for thyroid Ca/thyrotoxicosis
- new developments monoclonal antibody conjugated with radioisotope molecule to Tx non Hodgkin lymphoma.
Name some acute adverse effects of radiotherapy
Damage to epitheilal surfaces (skin, oral, bowel)
Oedema & swelling of soft tissues
Infertility - damage to radiation sensitive gonads
Generalised fatigue (80%)
N+V (60%)
Diarrhoea (60%)
Long term effects
Fibrosis hair loss dryness as result of damage to salivary glands or vaginal dryness dmaage to cerival glands Fatigue + lethargy cancer secondary to irridation death
What is the typical magnetic field strength of an MRI scanner used routinely in UK hospitals?
The majority of MRI scanners in UK hospitals are 1.5 to 3.0T.
What frequency would typically be used for monopolar diathermy?
The frequency must be greater than 100 KHz. 500 KHz is typically used.
Below this depolarisation (electric shock) can occur. Household frequency is around 60 KHz.
Early pregnancy USS:
What gestation can you see the gestational sac - how big is it
4 weeks + 3 Days
Early pregnancy USS:
What gestation can you see the yolk sac
how big is the gestational sac
5- 5+3 weeks
10mm
Early pregnancy USS:
What gestation can you see the embryonic pole
how big is the gestational sac
5+3-6 weeks
16mm
At what gestation does the fetal heart first become detectable on ultrasound?
6 weeks
The yolk sac reaches its maximum diameter at what week of gestation?
10 weeks
What are the definitions of oligohydraminos and polyhydramions on measurement of the AFI?
AFI involves measuring the depth of amniotic fluid pockets in all 4 quadrants.
Oligohydramnios AFI< 5cm or deepest amniotic fluid pocket < 2cm
Polyhydramnios AFI > 25cm or deepest amniotic fluid pocket > 8cm
How much radiation is in an chest XRAY compared to background radiation
A chest XRAY iss equivalent to 2.4 days natural background radiation.
What is the normal dose of external radiothe
Total dose varies between tumour type and stage but typical regimes involve 1.8-2.0 Gy fractions delivered over a number of weeks with total dose accumulating to reach around 50 Gy
