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1. Regarding ultrasonic waves:
True
False
The velocity in all tissues is constant.
Sound travels faster in a vacuum.
The velocity of sound through the human body is slowest through bone.
In constructive interference, the amplitude of the resulting wave is higher than the interfering waves.
Focusing improves the axial resolution at the depth of interest.
1. False, it is effected by tissue density/compressibility
2. False, sound is unable to travel in the lack of a transmitting medium.
3. False, the velocity is highest in bone.
4. True, hence the term “constructiveâ€.
5. False, this will enhance lateral resolution.
2. Beta particles:
True
False
Are negatively charged particles.
They lack an electrical charge.
β – decay occurs in neutron deficient nuclides.
β + decay occurs in cases of neutron excess.
Are non ionizing.
1. False, positively charged beta particles exist in the form of positrons.
2. False, their charge is equal to e=electron charge, and can be of negative or positive signs
3. False, -ve decay occurs in neutron rich nuclides.
4. False, =ve decay occurs in neutron deficient nuclides, when a proton transforms into a neutron emitting a positron.
5. False, they are a form of ionizing radiation.
3. Regarding effects of radiation:
True
False
Skin erythema is a stochastic effect.
The higher the dose the more aggressive the cancer induced.
Irradiating any part of the body will cause the same amount of radiation induced damage.
The human skin is radioresistant.
Deterministic effects are common in medical imagine.
1. False, it is deterministic with a threshold for erythema and dry desquamation at about 4 Sv.
2. False, the probability of inducing a cancer is predicted to increase with the increased dose (linear function of the dose). The nature of the cancer and its histological typing is statistically unpredictable.
3. False, the amount of damage is determined by the the dose, volume of tissue irradiated, the rate at which this dose was delivered and the type of tissue involved. So the amount of damage will depend on the tissue composition of every body part irradiated with some parts of the body being more radiosensitive than others.
4. False, all living tissue is susceptible to radiation damage. The deterministic threshold for the skin is 4 Sv.
5. False, dose limits are set well below the deterministic thresholds, so these effects should not be seen in routine medical exposures.
4. Answer true or false to the following:
True
False
Only beta particles can cause ionization in tissue.
The range of photoelectrons in matter increases with an increase in its initial energy.
Gamma rays are produced by electron bombardment of a suitable target in a vacuum tube.
Gamma rays are usually of low energy.
Gamma decay usually follows another form of decay.
1. False, this is a property shared by all types of ionizing radiations.
2. True, given the density of the matter remains constant.
3. False, gamma rays are a result of gamma decay. The question describes x-ray production.
4. False, gamma rays usually have energy of 100 KeV.
5. True, an initial particulate decay usually precedes a gamma decay leaving the nucleus in an unstable energy status which it compensates for by emitting a gamma ray.
5. The ideal radiopharmaceutical:
True
False
Produces very low energy gamma rays (<20 KeV) in order to keep the patients dose to a minimum.
Has a short effective half-live.
Would produce gamma rays with a very high HVL.
Has a photon energy between 100 & 200 keV.
Can be chemically incorporated in a number of stable compounds.
1. False, at these energy levels, a significant proportion of the rays will struggle to leave the patient. Gamma rays are also typically of energies >100 KeV.
2. True, as long that it is long enough to allow the diagnostic information to be gathered.
3. False, this means that these rays would be of very high energy which would make stopping them by the receptor to produce a picture technically very difficult as they will be very penetrating.
4. True, too low and will significantly increase patient dose, while too high will reduce attenuation within the gamma detectors.
5. True, to produce a variety of stable radiopharmaceuticals.
6. In mammography:
True
False
Tungsten can be used as a target material.
Breast compression is rarely used in modern practice.
High HVL beams are used.
The mammography system aims to optimise both spatial and contrast resolution.
An air gap can be used to improve contrast resolution.
1. True
2. False
3. False, low energy sets are used.
4. True, both are very important to visualize fine detail and subtle differences in tissue contrast.
5. True, by reducing the amount of scatter reaching the receptor.
7. Resolution of an image intensifier:
True
False
Is measured in pixels.
Is superior to conventional film.
Resolution improves by using a thicker input phosphor.
The input screen liberates electrons when stimulated by x-rays.
The output phosphor liberates light when bombarded by light photons.
1. False, it is usually measured in lp/mm.
2. False, spatial resolution of conventional film is much superior to the best achieved by image intensifiers.
3. False, the thinner the phosphor the better the spatial resolution as this limits light spread.
4. True
5. False, the output phosphor liberate light in response to bombardment by accelerated electrons.
8. In computed tomography:
True
False
The CT number fat is higher than water.
Attenuation in aluminium is the reference value used to calculate the HU units of tissue.
The spatial resolution of CT is low at around 1 lp/mm.
High levels of scatter usually reach the CT detectors.
The CT number of iodinated contrast is +5000.
1. False
2. False, water is the reference material with a value for pure water of 0 HU.
3. True, a deficiency that CT compensates for by superior contrast resolution and easier anatomical localisation.
4. False, CTs are very effective in eliminating scatter via the use of thin collimators. This is the main contributing factor to their superior contrast resolution.
5. False, the typical Hounsfield value spectrum ranges from -1000 to +1000.
9. Regarding CT development:
True
False
First generation scanners used a single detector.
The 1st generation scanners utilised a 360 spiral motion for imaging.
An electron beam bombards a ring target to generate X-rays in the 5th generation scanners.
3rd generation scanners succeeded in eliminating noise.
4th generation scanners use a complete stationary ring of receptors.
1. True, and a single pencil beam.
2. False, they used a rotate-translate action.
3. True
4. False, is an inherent property of the random nature of x-ray production and cannot be eliminated.
5. True
10. In diagnostic ultrasound:
True
False
High frequency probes are used to explore deep structures.
Doppler US can only provide you with information regarding the direction of flow.
Bowel gas acts as a good acoustic window, through which the operator can visualise the retro peritoneal structures.
Curvilinear array probes provide a wider field of view “sector width†when compared to linear probes.
Contrast enhanced US utilises iodinated contrast medium.
1. False, high frequency beams suffer more attenuation so are unable to penetrate to reach deeper structures. Low frequency probes are standard for abdominal imaging.
2. False, the main utilisation of doppler is to measure the speed of flow alongside the direction.
3. False, bowel gas is hyper-reflective and usually acts as an acoustic barrier.
4. True
5. False, special US microbubble agents are used. The microsphere gas filled bubbles are hyperechoic, and well visualised by US.
11. Ultrasound used in medical diagnosis:
True
False
Generates large amounts of heat in the imaged tissues.
Has an average speed in tissue of 1540 m/s.
Can cause tissue damage.
Has a frequency range of 1-20 Hz.
Can be used to measure blood velocity.
1. False, medical US generate negligible amounts of heat in the tissue.
2. True
3. True, that is why safety rules are in place to guard the patients against the potential risks associated with US.
4. False, the frequency range of diagnostic US are in MHz.
5. True, the doppler principle is utilized for this purpose.
12. Regarding medical US:
True
False
A cesium iodide crystal is used to produce diagnostic range US waves.
Setting the focus at the depth of interest will improve the resolution at this level.
The velocity of US in fat is equal to that in muscle.
High frequency probes are used in endoscopic ultrasound.
The absorption coefficient for fat is higher than water.
1. False, cesium iodide is an x-ray sensitive phosphor.
2. True, the acoustic focus is where the beam width is narrowest which improves lateral resolution.
3. False, there is small variations in the speed of sound in different tissue types in the human body. This is mainly related to the density and compressibility of the tissue.
4. True, penetration is sacrificed for higher resolution which allows depiction of mucosal and mural layers.
5. True, water is a very good media for US propagation.
13. Regarding MRI:
True
False
T2* relaxation takes a very long time which limits its practical diagnostic value.
The rephrasing pulse in usually a 180 degree one.
FLAIR stands for Fluid Attenuation Induction and Recovery.
The TR used to obtain T1W images is usually long.
T1 relaxation happens first closely followed by the initiating of T2 relaxation.
1. False, T2* is very short, typically shorter than T1 and T2.
2. True, for spin echo.
3. False, FLAIR is an inversion recovery sequence and is short for Fluid Attenuation Inversion Recovery.
4. False, short TR and TE values are used to obtain T1W images.
5. False, T1 and T2 relaxations happen simultaneously.
14. Regarding filters:
True
False
Combined filters are used in mammography.
No filters are used in mammography.
Aluminium is the filtering material of choice in most typical conventional x-ray sets.
Using a filter will reduce the patient’s skin dose.
Lead is used as a filter in fluoroscopy.
1. False, combined filters are where a second filter is used to absorb the characteristic radiation of the first higher atomic number filter. These interaction usually happens in high kV techniques (e.g copper/aluminium filter commonly used in CT). Mammography is a low Kv technique.
2. False, filters are commonly used in mammography (e.g. molybdenum filter with a molybdenum target combo).
3. True
4. True, the filter will harden the beam by principally removing the lower energy rays which mainly contribute to the patient’s skin dose and almost nothing to the final image.
5. False, lead is used as shielding material and not for filtration.
15. Regarding radioactivity:
True
False
Technetium 99m used in medical imaging is a pure beta emitter.
Molybdenum 99 gamma decays to technetium 99m.
Positron emitters are not used in medical imaging.
Taking more images using the gamma camera will significantly increase the patient’s dose.
The energy of the rays produced by technetium 99m is 140 KeV.
1. False, it is a pure gamma emitter.
2. False, molybdenum-99 beta decays to technetium-99m.
3. False, PET is based on positron emission.
4. False, the dose is the property of the radiopharmaceutical. So once this is administered, the number of images taken after that have no effect on the final dose.
5. True
16. Regarding X-ray production:
True
False
A large focal spot will produce sharper images.
Tungsten is used in both the anode and the cathode filament.
The cathode filament is heated to 200°c for it to emit electrons.
Gamma rays and x-rays are physically indistinguishable.
Oil is used to insulate the tube.
1. False
2. True
3. False, it usually reaches temperatures of 2000°c.
4. True
5. True
17. Increasing the Kv of the beam:
True
False
Will make it less penetrating.
For the same receptor dose, will result in an increase in the patient’s skin dose.
Will increase the amount of scatter reaching the receptor.
Usually will necessitate a use of a grid or an air gap.
Is the mainstay of mammography.
1. False
2. False, the beam will become more penetrating leading to less deposition of energy in the patient’s skin for the same receptor dose.
3. True, a high Kv beam will generate more forward scatter which is more likely to reach the film reducing its contrast resolution.
4. True, this is to compensate for the increase in forward scatter.
5. False, mammography is typically a low kV technique.
18. Regarding regulations:
True
False
Machine maintenance is the responsibility of the operator.
Every controlled area should be governed by a set of local rules.
If in a certain area an employee is likely to receive more than 6 mSv per year, this should be designated as a controlled area.
It is the responsibility of the employee to follow local rules and to utilize protective clothing and equipment provided by the employer.
The annual dose limit for a <18 year trainee is 6 mSv.
1. False, it is the responsibility of the employer.
2. True
3. True
4. True
5. True
19. In computed tomography:
True
False
Using bigger sized voxels will increase the spatial resolution.
Spatial resolution is greater than in plain films.
A CT of the head delivers the same dose to the patient as a typical barium enema.
Noise is reduced by reducing the tube mAs.
Multiplanar reconstructions increase the dose to the patient.
1. False
2. False
3. False, a typical barium enema delivers more dose than a CT head (7.0 vs 2.0 mSv).
4. False, reducing the mAs will reduce the signal reaching the receptors and will lead to noisier images.
5. False, multiplanar reconstructions are computer generated from the raw data after the scan has finished. This adds no extra dose to the patient.
20. Regarding MR:
True
False
The temperature inside a super conducting magnet is kept at absolute zero usually using liquid helium.
Only hydrogen protons can be imaged using MRI.
Gadolinium reduces T2 relaxation times.
The longitudinal relaxation time is always longer than the transverse relaxation time.
A short Te and a long Tr is used to produce a proton density image.
1. False, the temperature in an MRI superconducting magnet is kept using liquid helium at 4K.
2. False, theoretically any magnetically active nucleus can be used to produce MRI images (e.g. carbon, phosphorus, sodium).
3. True, gadolinium shortens both T1 and T2 relaxation times.
4. True, T1 is always longer than T2 in diagnostic MRI.
5. True
Your total score:
