quizz

1. Which is true regarding the specific ionization of an alpha particle?

• • It yields on the order of 100s of ion pars per mm

• • It yields on the order of 10s of ion pars per mm

• • It yields on the order of 1,000s of ion pars per mm

• It yields on the order few to no ion pairs per mm

• • It yields on the order of 1s of ion pars per mm

Answer explanation

Alpha particles are highly ionizing producing on the order of 5,000 ion pairs per millimeter.

2. What is the SI unit for KERMA

• • Sievert

• • Rad

• Gy

• Roentgen

• Select all modes of decay which are likely to result in production of an alpha particle.

• • Fusion

• • Beta- Decay

• • Internal Conversion

• • Alpha decay

Answer explanation

Alpha decay is named for its emission of an alpha particle so that one was kind of free. Additionally, deuterium-tritium fusion results in creation of a helium nucleus (aka an alpha particle).

4. What type of dosimeter stores charge carriers in crystalline energy traps until readout?

• • Luminescent dosimeters

• • Ion chambers

• • Bang-gel dosimeters

• • Radiochromic film

Answer explanation

Luminescent dosimeters such as OSLDs and TLDs store charge carriers in "trap centers" until heat or light allows the charge carriers to escape and subsequently emit light.

5. Rank these common dosimeters from best to worst dosimetric accuracy.

1. A. Radiochromic film

2. B. Radiographic film

3. C. Ionization chamber

• • B, A, C

• • A, B, C

• • C, B, A

• • A, C, B

• • C, A, B

Answer explanation

ionization chambers can achieve an accuracy of under 1% in ideal conditions.

Radiochromic film achieves an accuracy of 2-3% while radiographic film is only accurate to around 3-5%.

Radiochromic film is more accurate than radiographic film because it is self developing which eliminates errors associated with chemical development.

6. Which of the follow is not an advantage of radiochromic film over radiographic film for the purpose of x-ray and electron dosimetry?

• Its response is more linear.

• It does not require chemical based post processing

• It requires lower dose to achieve accurately measurable change in optical density

• It is more tissue equivalent

7. What is the cause of this MRI artifact?

 

• • Faulty k-space reconstruction

• • Non-uniformity of magnetic field

• • Frequency encode timing error

• • Aliasing of returning RF signal

8. What CT dose index attempts to account for changes in scan pitch?

 

• • DLP

• • CTDI_vol

• • CTDI_W

• • CTDI₁₀₀

 The value of a certain CT scan's Hounsfield number depends upon what? (select all that apply)

• • Linear Attenuation Coefficient

• • Photon beam quality

• • Atomic Number

• • Physical Density

An ultrasound pulse is 5 wavelengths long and has a wavelength in soft tissue of 0.3mm. What is the maximum achievable axial soft tissue resolution?

• • 0.67mm

• • 1.5mm

• • 0.75mm

• • 0.5mm

Answer explanation

Maximum axial resolution = 1/2 × spatial pulse length.
Spatial pulse length = n (wavelengths) × wavelength = 5 × 0.3mm = 1.5mm
Maximum axial resolution = 0.5 × 1.5mm = 0.75mm