Biophysics Flashcards
1
Q
What does the p wave represent on an ECG?
A
Atrial depolarisation
2
Q
What does the QRS represent on an ECG?
A
Ventricular depolarisation (atrial repolarisation takes place at the same time)
3
Q
What does the T wave present on an ECG?
A
Ventricular repolarisation
4
Q
At what rate is an ECG recorded?
A
25mm/second
5
Q
How long does a large square on an ECG represent?
A
0.2 seconds
6
Q
How long does a little square on an ECG represent?
A
0.04 seconds
7
Q
Which leads measure electrical heart activity in the frontal plane?
A
Limb leads (I, II, III) and augmented voltage leads (aVR, AVL, aVF)
8
Q
Which leads measure electrical heart activity in the horizontal plane?
A
Chest leads - V1-V6
9
Q
Which leads represent the lateral heart?
A
I, aVL, V5-V6
10
Q
Which leads represent the septal part of the heart?
A
V1-V2
11
Q
Which leads represent the anterior part of the heart?
A
V3-V4
12
Q
Which leads represent the inferior heart?
A
II, III, aVF
13
Q
What is the normal duration of the PR interval?
A
0.12-0.2 seconds
14
Q
What is the normal duration of the QRS interval?
A
<0.12 seconds
15
Q
What are the advantages of USS?
A
1) Non-invasive
2) Does not use ionising radiation
16
Q
What are the functions of USS?
A
1) Determining the nature of tissues, e.g. cystic vs. solid
2) Assessing movement of tissues
3) Measurement of blood flow
4) Measurement of structures
17
Q
At what frequencies are sound waves considered ultrasound?
A
Frequencies >20kHz
18
Q
What is the frequency range used in abdominal USS?
A
1-5 MHz
19
Q
What is the frequency range used in transvaginal USS?
A
5-10 MHz
20
Q
How is ultrasound generated?
A
By generation of a pressure wave - a pressure wave being generated by a piezoelectric crystal placed in the transducer that contacts tissue under investigation. Piezoelectric crystals convert electrical energy to mechanical energy.
21
Q
What are the 2 types of ultrasound?
A
1) Continuous-wave ultrasound
2) Pulsed-wave ultrasound
22
Q
Which type of ultrasound is used for imaging purposes?
A
Pulsed-wave ultrasound
23
Q
What are the three principle interactions of ultrasound with tissue?
A
1) Reflection
2) Scatter
3) Absorption
24
Q
What tissue properties determine the degree of reflection?
A
The acoustic impedance - which is the density if the tissue (p), multiplied by the velocity of ultrasound in that particular tissue (c)
Z = p x c
The greater the difference in acoustic impedance between tissues, the greater the degree of reflection.
25
When does scatter occur?
When ultrasound interacts with structures with smaller dimensions than the wavelength of the ultrasound wave.
26
What is absorption with regard to ultrasound?
Absorption is the conversion of mechanical (ultrasound) energy into heat. Absorption increases with frequency.
27
What are the limitations of real-time (B-mode) USS scanning?
1) Inadequate spatial resolution
2) Inadequate penetration
3) Poor image quality
4) Low frame rate
5) Compromised field of view
6) Low line density
28
What is spatial resolution?
= the min distance between two reflectors that is necessary to be able to distinguish two separate echo signals.
29
What is spatial resolution determined by?
1) Axial resolution - determined by pulse length
2) Lateral resolution - determined by beam width
3) Slice thickness - determined by thickness of the transducer and therefore transducer design.
30
What factors influence ultrasound penetration?
Absorption and scatter
Absorption and scatter both increase with increased frequencies and therefore better penetration requires lower frequencies (and therefore better penetration = poorer resolution)
31
What information can doppler ultrasound yield?
1) Speed at which the target is moving
| 2) Direction of the motion
32
What is doppler frequency shift?
The difference in frequency between the returning echo and the transmitted ultrasound wave. It is used to assess blood flow.
33
What is a colour flow scanner?
Combines real-time B-mode imaging ultrasound with pulsed-wave doppler and colour flow imaging. Used to assess blood flow.
34
What does red on a colour flow scanner represent?
Flow TOWARDS the transducer
35
What does blue on a colour flow scanner represent?
Flow AWAY from the transducer
36
How are differing velocities represented on colour flow scanners?
Dark hues = low velocity
| Bright hues = high velocity
37
What are the bioeffects of ultrasound?
1) Heating
| 2) Cavitation
38
What is the 'thermal index' with regard to ultrasound?
It is an estimate of the rise in tissue temperature that might be possible in a 'reasonable worst-case scenario'. The operator should continually monitor the thermal index and keep it as low as is consistent with achieving a diagnostic result.
39
What are the three types of thermal index?
TIS - thermal index in soft tissues
TIB - thermal index in bone
TIC - thermal index in cranium
40
Which type of thermal index should you be monitoring in O&G?
TIS in scans in first 8/40
| TIB in all other and subsequent scans
41
What is cavitation?
The lysing/damage of cells as a result of ultrasound
42
What is the wavelength rage of an x-ray?
10-0.1nm
43
What is the energy range of an x-ray?
120eV to 120keV
44
What is the difference between soft and hard x-rays?
Soft x-rays = energy <12keV
| Hard x-rays = energy >12keV
45
How are x-rays produced?
Accelerating electron collide with a metal target --- deceleration on collision results in electrons from the inner shell of the metal atom being knocked off ---electrons from higher energy levels fill up the space and x-ray photons are emitted as a result?
46
What are the advantages of computed x-rays?
1) Do not require on-site wet processing facilities
2) Do not require non-renewable silver
3) Easier archiving/retrieval of images
4) Space-saving
47
What is the radiation dose of a hysterosalpingogram?
1mSv = 4 months of background radiation
48
What are the advantages of hysterosalpingogram?
1) Complications rare
2) Relatively quick
3) Valuable information re: tubal patency
49
What are the risks of hysterosalpingogram?
1) Small risk of cancer from radiation exposure
2) Flare-up of undiagnosed chronic PID
3) inadvertent exposure of an unsuspected early pregnancy to radiation
4) Small teratogenic risk associated with ovarian radiation
50
What is CT used for in gynaecology?
Assessment of pelvic tumours
51
How does MRI work?
Magnetic field aligns protons present in the water (H2O) molecules of tissues --- a radiofrequency pulse is then used to disrupt the alignment of these protons --- following the pulse the protons drift back into alignment emitting a detectable radiofrequency signal
52
How does spatial resolution in MRI compare to CT?
Spatial resolution - the ability to distinguish between two structures very close together as separate - is comparable to that of CT
53
How does contrast resolution in MRI compare to CT?
Contrast resolution - the ability to distinguish between two similar but not identical tissues - is better in MRI compared to CT
54
What is the current view on contrasts used in MRI in pregnancy?
Gadolinium-based agents are known to cross the placenta, however they appear to be safe, any gadolinium reaching the fetus being rapidly eliminated in urine. Therefore, such studies should be considered if important for the health of the mother
55
What type of USS surgery is MRI guided?
Uterine fibroids - MRI being used to target ultrasound beams. Ultrasound increases tissue temp to >65 degrees C, destroying it.
56
What are the disadvantages of MRI?
1) Claustrophobia
2) Noisy
3) Contraindicated in those with metal clips/pacing wires/metal fragments etc.
57
How does a diathermy machine work?
Converts mains low-frequency current - approx. 50Hz - into high frequency current ranging 200kHz-3.3MHz.
58
What can be achieved by diathermy?
Cutting, coagulation, vaporisation and/or destruction.
59
What is monopolar surgical diathermy?
The electric current is transported through the human body and back to the generator.
The electrode may take the form of a blade, ball, are needle tip or a loop.
60
What is bipolar diathermy?
When the current flow between the tips of forceps blades. One blade acts are the active electrode, the other as a return.
61
What are the differences in what can be achieved by monopolar vs. bipolar diathermy?
```
Monopolar = cutting or coagulations
Bipolar = coagulation only
```
62
What type of electric current is used for cutting modes?
A low voltage continuous unmodulated sinusoidal waveform.
Electric arcs form between the tissue and the cutting electrode just above the tissue, produces a temperature such that cells are vaporised and a clean cut is achieved.
63
What type of electric current is used for coagulation modes?
A high voltage current that is applied intermittently and modulated with a duty current - the modulation (or dampening) allows the tissue to cool between heating bursts and so no vaporisation occurs
64
What is fulguration?
When high-powered current is used to produce a sparking effect to coagulate a large bleeding area or to char a tissue without touching it. Produces a deeper coagulation and is used in specific circumstances only.
65
Which is safer, monopolar or bipolar diathermy?
Bipolar
66
What are the hazards associated with monopolar diathermy?
1) Direct coupling
2) Insulation failure
3) Capacitive coupling
67
What is direct coupling?
When electrode activated next to/in contact with another conductive instrument in the body
68
What is insulation failure?
When the coating that covers the active electrode is compromised
69
What is capacitive coupling?
May occur between two conductors separated by an insulator - the electric current can be passed through the insulation into the other conductor and the electrical energy can be discharged into tissue structures it is in contact with
70
What does 'LASER' stand for?
```
Light
Amplification by
Stimulated
Emission of
Radiation
```
71
What are the different types of lasers?
1) Gas - e.g. CO2 or argon
| 2) Solid-state
72
What is the wavelength of CO2 lasers?
10 600nm
73
Are CO2 lasers suitable for laparoscopic surgery?
No, because their depth is very limited
74
What are the limitations of external beam radiotherapy?
1) Inability to identify microscopic disease accurately
2) Difficulty in immobilising the treated person/tumour
3) Problems arising from tumour shrinkage
75
What are the different forms of internally-delivered radiotherapy?
1) Sealed-source radiotherapy
| 2) Unsealed-source radiotherapy
76
Which type of internal-beam radiotherapy is brachytherapy?
Sealed-source
77
In what types of gynaecological cancer is brachytherapy used?
Vaginal, cervical, ovarian and uterine
78
Which isotopes are used in gynae brachytherapy?
Caesium-137
| Iridium-192
79
What type of internal-beam radiotherapy is radioisotope therapy?
Unsealed-course (delivered by injection)
80
What are the acute adverse effects of radiotherapy?
1) Damage to epithelial surfaces
2) oedema and swelling of soft tissues
3) Infertility
4) Generalised fatigue
81
What are the medium/long-term effects of radiotherapy?
1) Fibrosis and scarring or irradiated tissues
2) Hair loss
3) Dryness
4) Fatigue and lethargy
5) Cancer secondary to irradiation
6) Death
82
How is oligohydramnios defined on scan?
AFI <5cm, or deepest amniotic pocket <2cm
83
How is polyhydramnios defined on scan?
AFI >25cm, or deepest amniotic pocket <8cm
84
What is a normal endometrial thickness in women in their reproductive years?
5-14mm
85
What is a normal endometrial thickness in post-menopausal women?
<4mm
86
What is the maximum diameter or a pre-ovulatory ovarian follicle?
25mm
87
What is the SI unit of abdorbed dose of ionising radiation?
Gray 9Gy)
88
What is the SI unti of equivalent dose of ionising radiation?
Sievert (Si)
89
What is telsa?
SI unit of magnetic strength
90
What is Becquerel?
SI unit of radioactive decay
91
When does a gestational sac become visible on TVS?
4+3/40, it is 3mm when visible
92
When does a yolk sac become visible on TVS?
5-5+3/40, it is 3mm when it becomes visible and the gestational sac is 10mm
93
When does the embryonic pole become visible on TVS?
5+3-6/40, it is 3mm when it becomes visible and the gestational sac is 16mm
94
When can the yolk sac be seen on transabdominal scan?
When the gestational sac reaches 20m, i.e. at 7/40
95
What are the 3 doppler modes?
1) Pulse; 2) Power; 3) Colour
96
What are the main disadvantages of power doppler?
No information on a) direction or b) velocity of flow
97
What are radiosensitizers?
They increase the effect of a given dose of radiation
98
What are the four main groups of radiosensitizers?
1) Oxygen
2) Hypoxic cell sensitizers
3) Halogenated pyrimidines
4) Bioreductive agents
99
What is the maximum normal diameter of the yolk sac on TVS?
6mm at 10/40. After 10/40 the yolk sac will gradually disappear. >6mm = suspicious for failed pregnancy
100
What is the CXR equivalence to background radiation?
2.4 days
101
What is the CT abdomen equivalence to background radiation?
2.7 years
102
What might you see on ECG in hypercalcaemia?
Short QT
103
What might you see on ECG in hypocalcaemia?
Long QT
104
What is the SI for magnetic flux?
Weber
105
On an ECG, what features would you likely see in WPW?
Short PR and delta waves
106
What is the laser of choice in HPV or CIN?
CO2
107
What is the laser of choice in TTTS?
Diode or ND:YAG
108
What are the different types of solid sate laser?
Nd YAG; Neodynium; Titanium sapphire
109
What are the different types of liquid laser?
Rodamine; Stibene; Coumarin
110
What are the different types of semiconductor laser?
Diode
111
What is the typical daily dose (fraction) of radiotherapy in cervical cancer?
1.8-2.0Gy
112
What frequency is usually used in monopolar diathermy?
500kHz
113
What is the mechanism of action of radiotherapy?
DNA damage via free radical generation
114
Why does diathermy not use frequencies less than 200kHz?
Because lower frequencies may cause depolarisation and may cause electric shock.
115
What is the typical magnetic field strength of an MRI scanner routinely used in the UK?
1.5-3.0T
116
When does the fetal heart first become detectable on USS?
6/40
117
At what time in the cycle of hystersalpingograms usually performed?
Day 6-12
118
What is the normal axis of the heart?
-30 to +90 degrees
119
What is T and Z scoring in DEXA scanning?
T score (compares the individual to a young adult where normal is greater than –1) and Z score (compares the individual to another individual of the same age and gender)
120
Which laser in gynaecology surgery is invisible and cannot be transmitted down fibre optic cable?
Carbon dioxide
121
At what temperature does necrosis occur?
44 oC
122
At what temperature does coagulation occur?
70 oC
123
At what temperature does desiccation occur?
90 oC
124
At what temperature does carbonisation occur?
200 oC
125
What can cause an elevated JVP with a normal waveform?
Right-sided heart failure
126
At what hCG level should an experienced sonogropher be able to see an intrauterine gestational sac on transvaginal USS?
1000
127
How does DEXA scanning work?
2 low dose X ray beams are emitted and the absorption of the soft tissue beam is subtracted from the total beam
128
What is the penetration and resolution of transvaginal scanning relative to transabdominal scanning?
Transvaginal scanning = better resolution, worse penetration
129
At what CRL would you expect to see a fetal heartbeat?
>2mm
130
How many x-ray beams are used in a DEXA scan?
x2 low-dose beams
131
What does a T-score between +1 and -1 indicate?
Normality
132
What does a T-score between -1 and -2.5 indicate?
Osteopenia
133
What is reflection with regard to USS?
The change in direction of a waveform at an interface between two different media
134
What is refraction?
Refraction is the change in direction of a wave due to a change in speed
135
What is diffraction?
Bending of waves around small obstacles
| Occurs when a wave encounters an obstacle that has a diameter comparible to its wavelength
136
What factors effect doppler shift?
1. Insonating frequency
2. Velocity of moving blood
3. Angle between sound beam and direction of moving blood
137
What is USS unable to image?
Bone
| Air
138
What are the three different types of doppler?
1. Pulse
2. Power
3. Colour
139
What does pulse doppler provide information on?
1) Direction of flow
2) Velocity of flow
3) Flow characteritics
140
What are the advantages of power doppler?
1) No angle dependancy
2) Higher sensitivity to detect low flow or small blood vessels
3) Better penetration
141
What are the disadvantages of power doppler?
1) No directional flow
| 2) No velocity information
142
What is the problem with pulse doppler?
It is angle dependant
143
At what gestation does the fetal spine become visible?
>9 weeks gestation
144
What nuchal thickness is a problem?
>6mm
145
What is a nuchal thickness >6mm associated with?
Chromosomal abnormalities
Cardiac abnormalities
Fetal viral infection
Rhesus incompatibility
146
What are the causes of polyhydramnios?
Increased fetal production - maternal DM, fetal anaemia, fetal AV malformation
Decreased fetal swallowing - UGI obstruction
147
What is asymmetrical growth restriction due to?
Uteroplacental insufficiency
148
What are the USS findings in uteroplacental insufficiency?
1) Uterine artery notches
2) Umbilical artery may have absent end-diastolic flow or reversed end diastolic flow
3) Fetal arterial redistribution
149
What are the causes of oligohydramnios?
1) Uteroplacental insufficiency
2) Amniotic membrane rupture
3) Abnormal fetal renal function
150
What is rachischisis?
Absence of neural tube
151
What is lemon sign on USS?
Abnormal scalloping of the frontal bones
152
What is banana sign on USS?
Crescent shaped cerebellum that produces
153
When is the fetus most sensitive to radiation?
25 weeks gestation
154
What is the radiation threshold for fetal malformation?
100-200mGy
155
What is fractionation?
Time between radiation doses - allows normal cells time to recover between treatments
Allows time for re-oxygenation of hypoxic tumour cells between treatments
156
What is the usual schedule of radiation in radiotherapy?
2Gy/day
157
How do CTPA and V/Q compare in terms of risk?
CTPA carries an increased risk of breast cancer
| V/Q scan has an increased fetal radiation dose - 3x greater than CTPA
