Biophysics Flashcards
What size does the gestational sac need to be to see the embryonic pole
When is the yolk sac visible
Typically when the GS is 16mm.
However, miscarriage not diagnosed until GS >25mm and fetal pole not seen
Yolk sac typically visible when GS 10mm
What are the following units measuring:
Grey
Sievert
Becquerel
Hertz
Tesla
Weber
Grey - unit of absorbed dose
Sievert - unit of equivalent dose
Becquerel - unit of radioactive decay
Hertz - frequency
Tesla - unit of magnetic field strength
Weber - magnetic flux
What is an XRAY?
How much radiation does a CXR give you?
How much radiation does an abdo CT give you?
Ionising Electromagnetic radiation
Frequency of 30 petahertz to 30 exahertz
CXR - 2.4 days natural background radiation
CT AP - 2.7 years
RADIOTHERAPY
How does radiotherapy work?
What are the most common side effects?
What are radiosensitisers?
What are radioprotectors?
What is radiotherapy dosing in?
What is the typical dose of RT?
Kills cells.
There are multiple beams to direct most of the radiation to the unheathy tissue rather than damaging healthy tissue.
Brachytherapy - localised RT
Acute side effects:
- Fatigue in 80%
- N&V 60%
- In pelvic - diarrhoea in 70%
- Moist skin desquamation
Chronic side effects:
- Fatigue in 30%
- Lymphoedema
- Fibrosis
- Myelodisplastic syndroes - about 10% of MDS is due to RT/chemo
Radiosensitisers - enhance effect of RT: PHOB
- Pramidines (halogenated)
- Hypoxic cell sensitisers
- Oxygen
- Bioreactive agents
Radioprotectors - not used much because risk of enhancing cancers. e.g. a Radioprotective would be a HYPOXIC environment because oxygen is radiosensitive
RT dosing is in Gray
Typical dose of RT is 1.8-2 Gy fractions over a number of weeks to delivery approx 50 Gy
With MRI, what is the SI unit measurement of:
- Magnetic field strength
- Magnetic flux
MFS - Tesla
MF - Weber
MRI
How does it work?
What is the unit of measurement?
What is T1/T2 and how does it appear on an MRI scan
How much does an MRI magnet generate a field of?
NON-IONISING RADIATION
A magnetic field is applied to tissue and this causes the protons to align. Radiofrequency waves are then sent throughout a tissue which causes the protons to spin. When radiofrequency waves are stopped they slow down and stop spinning. This happens at different rates depending on the tissue they are within. As they relax they release radiowaves of different frequencies. This is picked up by the MRI scanner.
Unit of magnetic field strength = Tesla
Unit of Magnetic flux = Weber
T1 = dark image
T2 = light image
MRI magnets generate a field of 0.5-3.0 tesla
What does the P, QRS, T and U represent in an ECG
P wave = Atrial depolarisation
QRS complex = Ventricular depolarisation
T wave = Ventricular repolarisation
U wave = repolarisation of the interventricular septum
What are the typical ECG features of:
Hyperkalaemia
Hypokalaemia
Hypercalcaemia
Hypocalcaemia
Hyperkalaemia:
- TTT waves
- Wide QRS
- Prolonged PR
- Flat P wave
Hypokalaemia
- Flat T waves
- U waves
- ST depression
Hypercalcaemia
- Short QT
Hypocalcaemia
- Long QT
What type of lasers are used in:
- precancerous genital lesions
- TTTS
Precancerous genital lesions/VIN - CO2 lasers
TTTS - Diode or ND:YAG
When does the yolk sac reach maximum diameter?
What is the maximum diameter? What if it gets bigger than this?
Can you see it on the 20 week scan?
Maximum diameter at 10 weeks
6mm
If >6mm ???failed pregnancy
Usually gone by 20 weeks scan
What is the maximum diameter of a follicle before it ovulates
25mm
What is the gestation when heart becomes visible?
6 weeks
Which of the following imaging methods are ionising:
Ultrasound
PET
CT
MRI
Xray
Laser
Iodine 131
Xray
CT
PET
Iodine 131
How does Ultrasound work
Sending high freuqency sound waves through tissue.
These waves are created by putting a voltage across a piezoelectric crystal.
The transducer directs the waves produced.
Different tissue reflect varying amounts of the waves based on density (or acoustic impedence).
Doppler uses direction to produce colour. The coloured image is called a duplex image.
How does CT work?
Contrast the radiation of an abdo CT with a CXR
Significant ionisation. Uses multiple XRAYS to create 3D image
Abdo CT = 400 CXRs
How does PET scanning work?
Uses a radioactive tracer, usually FDG which gets taken up by areas of high metabolism in the body - e.g. cancer. The tracer then emits gamma rays which are picked up by the PET scanner
FDG is an analogue of glucose
DIATHERMY
What is monopolar vs bipolar diathermy?
What can cause tissue burns?
What is the frequency used for diathermy?
Monopolar - current passed between two electrodes. One is the diathermy tip and the other is the plate on the patient (on the leg)
- COAG
- CUT
Bipolar - both electrodes are help by surgeon. E.g. forceps
- ONLY COAG
Tissue burns can happen if the plant is not applied correctly. It means that the surface area the current is spread over is not as big so can be condensed and cause tissue burns.
The frequency has to be over 100 kHz because otherwise cell depolarisation can occur and cause electric shock. Surgery typically uses 500 kHz
How is hysterosalpingography performed?
Who is it an appropriate test for?
What about for hx of PID?
Who is it contraindicated in?
When should it be performed?
What is the main alternative to HSO?
Uses Xrays with contrast. Can see moving image to assess patency of the tubes. Iodine based contrast
It is an appropriate test for people with no suggestion of tubal issue.
For people with hx suggestive of tubal issue - laparoscopy with dye testing is the test of choice
Contraindiacations:
- Pregnancy
- Active pelvic infection
Should be performed in follicular phase. After menses but before ovulation
The main alternative if a HYCOSY
- Uses ultrasound
- Uses iodine based contrast or saline based
What gestation does the gestational sac become visible on TVS?
How about yolk sac?
How about the embryonic pole?
How about heart beat?
4+3 weeks
5 weeks
5+3 weeks
6 weeks
Desrcibe the 3 modes of USS and their advantages/disadvantages
Power
- No information related to velocity or direction
- Detects flow in smaller vessels
- Better penetration
- Not angle dependant
Colour and Pulse
- Gives info about velocity and direction
- Worse penetration
- Angle dependant
Short PR and delta waves?
WPW
How do DEXA scans work?
TWO beams - hence the dual, with different freuqncies are directed at the same bone area. The higher the density, the more of the beam gets absorbed. The rest of the beam is picked up on a plate behind. The BMD is calculated minusing the soft tissue density
What is the doppler effect
How the waves re changed as they move away from trnsducer
What are the initial invetigations for urinary incontinence?
Hx and exam
Bladder diary 3 days
Post-void bladder scan
Urine dip
When are urodynamics indicated?
Before surgery in women who have:
- When symptoms suggest OAB
- OR symptoms suggest difficulty voiding
