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108 Cards in this Set
- Front
- Back
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1. Most radioresistant phase of cell cycle:
A. G1 B. M C. S D. G2 |
Answer – C
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2. Greatest lifetime risk of cancer is from which study?
E. 2 view CXR F. CT head G. Nuclear medicine bone scan H. Nuclear medicine V/Q scan I. Lateral lumbar spine film |
G. Nuclear medicine bone scan
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3. Which of the following populations got lung cancer (last two after radiation treatment)?
a. Uranium miners b. Radium dial workers c. Nagasaki bomb survivors d. Tuberculosis patients e. Ankylosing spondylitis patients |
a. Uranium miners
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4. What layer is most affected by radiation?
J. Endocardium K. Myocardium L. Pericardium M. Epicardium |
Answer – C PERICARDIUM
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Using ultrasound real-time imaging with phased array, beam aimed in different directions in space to create image. This is performed by:
A. Electronic steering of beam by applying timing delay to individual transducer elements B. Electronic steering of beam by applying different pulse amplitude of individual transducer elements C. The tech wiggling it back and forth |
A. Electronic steering of beam by applying timing delay to individual transducer elements
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In ultrasound, which of the following will decrease axial resolution?
N. Increased SPL O. Increased frequency P. Increased transducer diameter Q. Decreased wavelength |
Answer – N
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7. In ultrasound, with the same transducer, velocity changes from 1450 m/s to 1550 m/s. What changes?
o Wavelength increases o Wavelength decreases o Frequency increases o Frequency decreases |
• Answer – wavelength increases
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8. On an ultrasound image, what do the MI and TI values refer to?
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Answer – Mechanical Index (Cavitation) and Thermal Index
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9. In ultrasound, what is the purpose of time gain compensation?
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Answer – Compensate for increased attenuation with tissue depth
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10. What is an advantage of computed radiography over conventional radiography?
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Answer – Increased dynamic range
Other answers – decrease patient dose, increase spatial resolution |
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11. The mAs refers to what property of electrons?
• Number • Charge • Speed • Energy |
Answer: number
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12. What will increase signal to noise ratio in image with digital fluoroscopy?
• Windowing • Veiling glare • Logarithmic transformation • Hybrid subtraction • Frame integration |
Answer: frame integration
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13. Over 1 minute, 100 counts per minute were recorded. What is the standard deviation of counts per minute for a 95% confidence interval?
• 10 • 20 • 40 • 80 • 100 |
Answer: 20 (2 SD = 95% CI) -or range 80-120 for 95% CI?
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14. What causes chemical shift artifact?
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Answer – Small differences in resonance frequencies of different chemical compounds (water and fat)
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15. A patient is dosed with I-131 for Graves Disease. She finds out later that she was 18 weeks pregnant at the time of the I-131 dose. What is the most likely outcome for the fetus?
a. Cretinism b. Mental retardation c. No abnormalities are expected d. Benign and malignant thyroid neoplasms e. Hypothyroidism |
Answer: cretinism
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16. Which of the following materials would provide the best shielding from ß- particulate emissions from I-131 and give the lowest bremsstrahlung radiation production?
• Lead • Tungsten • Plastic • Copper |
Answer: plastic
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17. What can be expected following a skin dose of 2 mGy?
• Erythema • Epilation • Gastrointestinal syndrome |
Answer: erythema
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18. in PET scanning, how do the non-attenuation corrected images look?
• Darker/hotter than corrected images • Diffusely lower attenuation • SUV is accurate in the center • SUV is accurate in the periphery • Metal artifact is less apparent |
• SUV is accurate in the peripheryIn
PET/CT x-rays from a CT scan are used to construct an attenuation map of density differences throughout the body that can then be used to correct for the absorption of the photons emitted from FDG decay. Attenuation is much more likely in the center of the body and therefore non-attenuation-corrected images will show diffusely lower level activity deep in the body compared to the skin surface. The attenuation correction process essentially “adds counts back” into areas that are more attenuated due to their being deeper or being surrounded by relatively dense structures. Similarly, it essentially “subtracts counts” from areas that are attenuated much less than all other tissues (e.g. lungs and body surfaces). Both attenuation-corrected and non-attenuation-corrected data sets are provided for review and both should be examined by the interpreter. Reviewing both data sets sometimes allows confirmation of an abnormality or confirmation of the benignity of a process which might have been incorrectly assessed based on review of one set alone. |
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18 week pregnant female is in a car accident- gets AP & lateral L-spine xrays. How will this affect her fetus?
• Increase risk of stillbirth • Dose is 0.05-0.1 Gy • Affect organogenesis • Should not have had exam • No significant effect |
Answer: no significant effect
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19. Dose in MBq of 10^13 atoms of Tc99m (half life = 6hr; decay constant = 3*10^-5)
• 2*10^8 • 3*10^5 • 320 • 40 |
Answer: most of us picked 320- not sure
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20. You’re given a picture of k-space with the center of the k-space removed. Then you’re given five pictures of the brain: a. perfectly fine-looking image; b. slightly blurry image compared to a; c. substantially blurry image compared to b; d. only edge-outlines of the brain, ventricles, and calvarium noted, with significant gray-white matter and intensity information gone
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D
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21. Which one of the following single image would take up the most space in memory/storage?
a. chest xray b. digital subtraction angio c. ct image d. nucs e. mr |
a
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22. How much more storage do you need if you increase 256*256 to 1024*1024?
• 2 • 4 • 16 • 32 |
Answer: 16 times more
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23. How can you increase SNR (or spatial res- we can’t remember) without increasing the scan time?
• NEX • TE • TR • Frequency sampling |
Answer: Freq sampling
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24. Patient undergoing DSA of neck; she swallows during the exam. How do you correct for it?
• Re-mask • Log rhythmic • Increase frame integration |
Answer: Re-mask
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25. At what point do Tc and Mo reach a temporary equilibrium?
a. 24 hours b. 6 hours c. 135 hours d. 270 hours e. 1 week |
Answer: 24 hours
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26. Taking a digital CT image, blurring it, and subtracting it from the original image results in:
a. edge enhancement (i.e. unsharp masking). b. smoothing c. masking d. similar affect as using a low frequency filter |
Answer: edge enhancement
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27. How do you decrease scatter in SPECT?
• Collimator • Narrow the pulse height • Some other choices |
Answer: narrow the pulse height
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28. Why does PET scan have decreased scatter?
• Coincidence detection • A few answer choices with collimator • Smaller septa |
Answer: coincidence detection – (PET doesn’t use a collimator)
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29. Why do you scan longer in SPECT?
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• Because there is more noise with filtered backprojection
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30. Which of the following are safe to throw away after 1 year of storage?
• Mo • Tc • Ga • Co |
Answer: cobalt- half life is 256 (or something like that) days…
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31. Why can you use Co instead of Tc in QC testing in nucs?
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Answer: the photopeaks are similar
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32. In nucs, you are testing a point source at different angles of the collimator, for what?
• Uniformity from different angles • Centering • Spatial linearity |
Answer: Centering
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33. In a mammographic film, there is a dark spot on the image. What is it from?
a. Tattoo b. Fingerprint on the screen c. Deodorant d. Pressure on film after exposure |
Answer b – Fingerprint on the screen
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35. Poor film screen contact in mamms results in what?
• Lower spatial resolution • Slower speed • Poor contrast |
Answer: Poor contrast as well as lower spatial resolution
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36. MDCT- what affects reconstruction?
• Precollimator data • Postcollimator data • Detector row group |
• Detector row group
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37. Definition of linearity-
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?
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38. Standard deviation is what?
• Modal • Accuracy • Precision • Range |
• Range (spread)
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39. Comparing 2 sets of information, you use:
• Gaussian distribution • Poisson distribution • Chi-squared test • Students T-test • Standard deviation |
Answer: Students T-test
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40. There is a CR machine, if you turn the knob to N+2, what does that do? (we have no idea)
• Increase density • Decrease density • Increase contrast • Decrease contrast |
• Decrease contrast
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41. In teleradiology, sending the images fastest…??
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• Increased bandwith
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42. MRI image has a nose, wrapped around the back of the head. How do you get rid of it?
• Increase AP diameter of FOV • Fn |
Answer: Increase field of view
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43. What is the minification gain if the output phosphor is 1.5 inches and input phosphor is 9 inches in diameter, respectively?
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Answer: 36 : 9:1.5 = 6; 6*6=36
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46. How long after being given Tc-MAA, do you need to stop breastfeeding?
• Never • 12 hours • 48 hours • 1 week • discontinue |
Answer: 10 hrs is the recommended time to stop breast feeding until the milk is safe. So, since this was recalled incorrectly I would assume the question was something like the minimum time needed and then the answer would be 12 hours in this instance.
Tc-99m sodium 10 mCi Thyroid scan and 8.2 x 10_2 24 hr pertechnetate Meckel’s scan Tc-99m kits general 5-25 mCi All 8.2 x 102 24 hr rule Tc-99m DTPA 10-15 mCi Renal scan 1.2 x 10_i 17 hr Tc-99m MAA 3-5 mCi Lung perfusion 1.2 x 10 10 hr scan Tc-99m sulfur colloid 5 mCi Liver spleen scan 1.6 x 10_i 15 hr Tc-99m MDP 15-25 mCi Bone scan 2.1 x 10_i 17 hr Ga-67 citrate 6-10 mCi Infection and 2.1 x l0 4 wk tumor scans Tl-201 Chloride 3 mCi Myocardial 2.4 x io-3 3 wk perfusion Sodium 1-123 30 pCi Thyroid uptake 1.2 x 10 3 days 50-400 pCi Thyroid scan 5 days Sodium 1-131 5 pCi Thyroid uptake 4.1 x io 68 days 10 mCi Thyroid cancer Discontinue" Scan or Graves therapy 33 mCi Outpatient " Discontinue" therapy for hyperfunctioning nodule 100 mCi or Thyroid cancer " Discontinue" more treatment ablation |
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44. Temporal resolution in ultrasound
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temporal resolution (frame rate) is = to
(77000/sec)/(N X D) where N = the number of a lines per image and D is = depth. So, in order to increase frame rate you can - decrease depth - decrease FOV - decrease line density - decrease number of lines per image |
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47. How to you decrease inhomogenities in MR?
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Answer: shim coils
Shim coils are active or passive magnetic field devices that are used to adjust the main magnetic field and to improve the homogeneity in the sensitive central vol ume of the scanner. Dephasing owing to the inhomogeneity contribution to T2* can be overcome by generating spin-echoes (SEs), whereas signal loss owing to true T2 relaxation is ir- reversible. |
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48. What is the ideal kVp for DSA with iodine?
• 70 • 100 • 120 • 50 |
Answer:
The two X-ray contrast media iodine and barium have ideal K shell binding energies for absorption of X-rays, 33.2 keV and 37.4 keV, respectively, which is close to the mean energy of most diagnostic X-ray beams. The mean energy of the beam is 1/3 to ½ peak kvp. Not entirely sure the question is recalled correctly. I would guess 70 kvp. |
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49. Why do we use filters in personnel dosimetry badges?
• Estimate energy • Different ranges of energy • Different range of doses |
Answer: because you can detect a wider range of energies
-The sensitivity of film to x-rays depends on photon energy. -The response of film at 60 kVp is as much as 100 times higher than the response of film at 1 MeV (cobalt 60 energy levels) for the same exposure. -This enhanced sensitivity arises at the K-edge of the silver in film at 25 keV. -Personnel monitoring devices are worn to ensure that workers receive doses below the appropriate dose limit and to monitor radiation safety practices. -Film badges consist of a small case with a piece of film placed between filters. -An estimate of photon energy is needed because the film response is energy de- pendent and is obtained by the use of three filters in front of the film. -The filters assess the penetrating power of the radiation source, thus permitting the energy to be estimated. -The film is processed and the optical density measured to estimate dose based on the average photon energy. -The minimum dose that a film badge can detect is approximately 0.2 mGy (20 mrad). |
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50. Where do you count the daily wipe testing?
• Well counter • Thyroid probe • Some other choices |
Answer: well counter
-Wipe tests should be performed of radionuclide use areas where a small piece of fil- ter paper is wiped on an area and checked in a Nal gamma well counter. |
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52. Which of the following has a short latent period for radiation induced cancer?
• Leukemia • Thyroid Ca • Sarcoma |
Answer: Leukemia
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51. What do x-ray machines use to measure dose?
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-Ionization chambers are used as phototimers in automatic exposure controls and as
dose calibrators in nuclear medicine. |
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53. Which of the following is the most radioresistant phase in the cell cycle?
• S • M • G1 • G2 |
Answer: S
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54. When using a gamma camera, how do you decrease scatter?
• Collimator • Pulse height analyzer |
Asnwer: PHA
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55. Using a parallel collimator, how do you increase spatial resolution?
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Answer: move pt closer to collimator
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56. What is the dose limits are correct?
• Non-occupational dose to extremity- 500 mSi • Occupational dose to thyroid- 500 mSi • Non-occupational dose to lens- 150 mSi • Occupational dose to extremity- 1000 mSi |
Answer: occupational dose to thyroid- 500 mSi
non occ dose to anything is 1msv/yr |
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57. Which of the following regarding the threshold for skin radiation is false?
• Cataracts- 2Gy • Hair loss- 1 Gy • Regular fluoroscopy can cause these effects • These are deterministic effects |
Asnwer: Hair loss @ 1 Gy- is the false statement
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58. When do you get temporary erythema?
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Answer: 2 Gy
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59. Which single image has the most dose/frame?
a. DSA b. Digital angio c. Fluoro d. Pulsed fluoro e. Last frame hold |
Answer: DSA. It needs 2 images.
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60. CT # depends on what?
• Linear attenutation coefficient • Mass attenuation coefficient |
Answer: LAC
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61. If you see a low contrast 4-cm liver lesion, how can you see it better?
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Answer: increase slice thickness
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62. If you look at a liver lesion with a bone window…
• Decrease contrast • Increase spatial resolution |
• Decrease contrast
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63. Syrinx seen in a sagittal MRI of the lumbar spine, is from what MRI artifact
• Truncation • Chemical shift • Aliasing • Partial volume averaging |
• Truncation
straight from huda -Truncation artifacts in the spinal cord may simulate a syrinx. |
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64. How is energy transferred to tissue?
• Electrons • Protons • Muons • Neutrons |
Answer: most of use chose electrons
-Charged particles lose energy when passing through matter by interacting with electrons in nearby atoms. -Electrons, positrons, protons, neutrons, and alpha particles are examples of ioniz- ing particles. -The loss of energy by a charged particle increases with increasing charge. -The loss of energy by a charged particle increases with increasing mass and de- creasing particle velocity. -Energy lost from energetic particles can eject electrons from atoms or raise atomic electrons to higher energies. |
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65. In “direct” DR, what do you use?
• Amorphous selenium • Cesium iodide |
Answer: amorphous selenium
-Selenium(Z = 34; K-edge energy = 13 keV) is the most common photoconductor in use in digital radiography. |
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66. What limits spatial resolution in CR?
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-The detector size (aperture) and sampling pitch of digital arrays both affect spatial
resolution. -For example, if there are 2,000 detectors on a line that is 35 em long, the sampling pitch is 175 p m (35 divided by 2,000). -The sampling pitch determines the limiting spatial resolution that is achievable by the digital imaging modality. -The limiting spatial resolution, also known as the Nyquist frequency, is given by the reciprocal of twice the sampling pitch, or 1/(2 X sampling pitch). -If the sampling pitch is 175 µm, the limiting (Nyquist) frequency is 2.9 lp/mm (i.e., 1/[2 X 0.175 mm]). -The Nyquist frequency defines the highest spatial frequency that can be faithfully reproduced. |
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67. How do you fix veiling glare artifact?
• Flux gain • Brightness gain • Contrast ratio • Kell factor |
Answer: contrast ratio
veiling glare loss of contrast due to light scattering in image intensifiers -The image intensifier contrast ratio is the ratio of periphery to central light inten- sities (output) when imaging a fully absorbing lead disc that is one tenth of the area of the image intensifier input phosphor. -The light appearing behind the image of the lead disk is called veiling glare. -A typical image intensifier contrast ratio is 20:1. -Loss of contrast occurs because some x-ray photons pass through the input phos- phor and photocathode, strike the inside of the II, and are scattered back to the in- put phosphor. Kell factor correction factor used to determine actual vertical resolution on a television sys- tem from the theoretical maximum resolution (70%) |
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68. Geometric unsharpness, how do you fix it?
• Exposure time • Focal spot |
Answer: focal spot
C. Focal spot blur -The blurred margin at the edge of objects is called the penumbra. -The penumbra is the result of x-rays arriving from slightly different locations in the focal spot, because the focal spot is not a true point source but has a finite area. -The resultant unsharpness is called focal spot blur or geometric unsharpness. -Focal spot blur increases with magnification and focal spot size, as shown in Fig. 5.2. -Reducing the focal spot size increases the sharpness and definition of object edges by minimizing the penumbra. -In magnification radiography, it is important to have very small focal spot sizes. -Magnification in mammography improves visibility of microcalcifications, but needs a 0.1 mm focal spot to minimize geometric unsharpness. -Magnification is sometimes used in angiograms to improve the visibility of very small blood vessels and makes use of a 0.3 mm focal spot. |
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70. What does scatter to primary ratio depend on?
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Scatter
-Scattered radiation is undesirable in diagnostic radiology because it reduces sub- ject contrast. -Of paramount significance are the scattered photons resulting from Compton scatter. -The ratio of scatter to primary radiation exiting a patient can easily be 5:1 or greater. -Scatter increases with increased field size (i.e., area of x-ray beam) and increased patient thickness. -Collimation reduces the total patient mass irradiated and therefore reduces scatter. -At low voltages (kVp), there is more absorption because of the photoelectric effect and less Compton scatter. -However, lowering the x-ray tube voltage reduces patient penetration and increases dose; therefore, it is not a practical method for reducing scatter. |
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71. In fluoro, if you go from 15” (mag) to 30” (regular)…
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Answer: decrease spatial resolution
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72. What does not contribute to pt dose?
• Coherent • Compton • Photoelectric effect • Characteristic electrons • Auger electrons |
Answer: coherent (rayleigh)
coherent scatter photon scattered by an atom without suffering any energy loss; also known as Rayleigh or classical scatter |
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73. Calcifications seen in mammograms are due to what?
• A • Density • Atomic number |
Answer: Atomic number
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74. CR vs screen film?
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Answer: greater dynamic range
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75. 100 counts in 1 minute. How many counts with a 95% confidence interval?
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Answer: 80-120 (remember 95% CI = 2 standard deviations)
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76. SPECT, you take all the images from 1 slice, and line them up…what is that?
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Sinogram
The data acquired for one Ct slice can be displayed before reconstruction. This type of display is called a sinogram Fig. 13-20. Sinograms are not used for clinical Purposes, but the concepts that they embody are interesting and relevant to under standing tomographic principles. The horizontal axis of the sinogram corresponds to the different rays in each projection. |
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77. To decrease entrance skin dose or increase exit skin dose…
• Keep pt-receptor distance same, and increase source-to-pt distance • Decrease HVL • Decrease filtration • Decrease mA • Increase kVp |
Answer: most of us picked, keep pt-receptor same, increase source to pt distance
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78. Radon
• Decays by beta • Outdoor levels >indoor levels • Daughter of Polonium • Dose is greatest after inhalation |
inhalation
Radon is an alpha emitter thus the dose is more significant when ingested or inhaled (travels very short distance) |
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79.
• A, Z+1 • A, Z-1 • A-1, Z-1 • A+1, Z+1 |
Answer: A, Z-1
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80. Pb (207) (Z=83), how many neutrons?
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207-83 = 124
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81. Preferential form of decay for scintillation cameras?
• Beta minus • Internal conversion • Auger electrons • Gamma |
Answer: gamma
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82. Deoxyhemaglobin on MR?
• Paramagnetic • Diamagnetic |
Answer: paramagnetic
Blood oxygen level-dependent BOLD and "functional MR" imaging rely on the differential contrast generated by blood metabolism in active areas of the brain. In flow of blood and conversion of oxyhemoglobin to deoxyhemoglobin a para magnetic agent increases the magnetic susceptibility in the localized area and induces signal loss by reducing T2*. |
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83. If a community has a low rate of lung cancer, and a radiologist calls all CXR negative...
• Increased accuracy • Low specificity • High PFP • High sensitivity |
• Increased accuracy
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84. What does standard deviation measure?
• Precision • Accuracy • Some other answer choices |
one of the other answers
The variance and standard deviation are measures of the -variability spread of a set of measurements. -Standard deviation (defined for a population) is used to describe the spread or dis- tribution of a data set and is the square root of the average of the square of all the sample deviations. standard deviation (SD) a measure of the spread of a statistical distribution |
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85. Daily QC for mamms
• Processor artifacts • Clean screen • Compression |
Answer: most of us put processor artifacts- it’s the most variable part of the whole process
-All major processor problems must be corrected before clinical work begins. -Screens and darkrooms must be cleaned every day. -Weekly tests include obtaining an image of the ACR phantom and assessment of viewbox and reading conditions. -The x-ray imaging equipment should be inspected every month. -Quarterly tests include a repeat analysis and analysis of fixer retention on film. -Repeat rates are expected to he between 2% and 5%, and caused by positioning, patient motion, and overexposure or underexposure. -Darkroom fog, screen/film contact, and compression testing is performed on a semiannual basis. |
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86. What accounts for the difference in attenuation along the cathode-anode axis?
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Answer: heel effect
Orientation of the cathode-anode axis is along the chest wall to nipple direction. The heel effect, a result of anode self-filtration, describes a significant falloff of intensity oward the anode side ot the x-ray beam. For this reason, the chest wall side of the breast the thicker part of the breast is positioned over the cathode to help equalize x-ray transmission. |
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87. Image with a c-arm fluoro machine, with a plastic tube attached to the xray tube housing. What is the tube?
• Spacer • Collimator • Protection for the tube |
unknown
they put spacer to protect patient major components include xray tube then filters then collimation then table patient grid ii aperture video cam |
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88. Image of the thyroid probe, and it pointed to the housing. What does it do?
• Form an image • Focus the gamma rays towards the crystal • Shields crystal from background radiation • Acts as collimator |
Acts as a collimator
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89. Best decay scheme for a scintillation camera
• Beta minus • Internal conversion • Electron capture • Auger electrons • Isomeric transition |
Answer: isomeric transition
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90. What is the graph…the x-axis labeled : mm-1, and the y-axis : has a maximum value of 1.0?
• MTF curve • ROC curve • H&D curve |
Answer: MTF
HD curve = A plot of the O.D. versus (logarithm) radiation exposure to film is known as the Hurter and Driffield (H&D) curve; |
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91. How do you decrease scatter in PET?
• Increase distance from collimator • Use higher energy collimator • Increase collimator septa thickness • Coincidence detection |
Answer: coincindence detection (PET scanners don’t use collimators)
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92. What is the proper kVp for mammography?
• 23-32 • 17-20 • 43-52 |
Answer: 23-32
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94. How do you increase temporal resolution in ultrasound?
• Increase depth • Decrease number of scan lines |
• Decrease number of scan lines
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What model do you use for radiation protection?
• Linear quadratic • Linear non-threshold • Stochastic |
Answer: linear non-threshold
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96. Know the difference between pulsed vs continuous ultrasound
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Pulsed is for imaging
Continuous is for treating not sure this was recalled correctly maybe they were talking about fluoro where pulsed uses less than real time to reduce dose. |
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97. In fluoro, what can cause distortion/artifact?
• Magnetic fields • RF energy • Problems with the monitor |
Answer: magnetic fields- shouldn’t have MR near fluoro room
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98. Which one of the following is true regarding free radicals?
• Originates in the cytoplasm • Affects DNA > cytoplasm • Small portion of the radiation effect |
Answer: DNA> cytoplasm
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. What increases the cellular affects of radiation?
• Actinomycin D • Tobacco • Hypothermia • Hypoxia |
Answer: actinomycin D
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100. Female 18-weeks pregnant, car accident, has AP and lateral L-spine xrays
• Abortion • Should not have been done • Pt received a dose of 0.5-1 Gy • Risk of fetal abn is 0.01% • If there is a defect, it occurred during organogenesis |
Answer: risk of fetal abn is 0.01%
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101. CT body, what is the dose to the center of the pt compared to entrance skin exposure?
• 20% • 50% • 10% • 1% • 0.05% |
• 50%
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102. Pt has a entrance skin exposure of 2 cGy/min, in fluoro, there is an exposure reaching the film/detector of 0.02 cGy/min. What is the dose at the center?
• 0.02 • 0.2 • 1 • 1.5 • 2 |
Answer: we didn’t know…we all had difference answer…I think some picked 10%…0.2
HVL of tissue is 2-3 cm - figure it out |
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103. Photoelectric effect is related to E by what?
• E • E2 • E3 • E-3 • Z |
Answer: E-3
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104. MRI question, FLAIR sequence- what are two important factors?
• TR, TE • TI, TE • TI, T1 • T2, TR |
Answer: T1, TI (inversion time)
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105. 10^13 atoms of Tc99m, how many MBq are in them? T1/2 = 6 hours; decay constant was also given
• 320 • 3*10-5 • 1*1010 |
Answer: 320
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106. In an average size breast, Mo-target and Rh-filter are used. How do you increase contrast?
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Answer: switch to Mo-Mo
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107. Mammography- grid lines are seen, why?
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Answer: exposure times are too short
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108. Proton density in MRI?
• Number of H1 in the tissue • All H nuclides in tissue • All nuclides in tissue |
Answer: all H nuclides in tissue
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109. What is the unit for cumulative activity
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Answer: microCi-hr or becquerel/second
Cumulative activity -The total number of nuclear transformations in an organ or tissue is called cumu- lative activity (A). -Cumulative activity is the area under a curve of activity in an organ or tissue plot- ted as a function of time. -The average life of a radioactive nucleus is 1.44 X T1J2 , or 1/X. -In the SI system, the number of transformations is expressed in becquerei -seconds (Bq-s) as 1.44 X initial activity in organ (13q) X T1/2 (seconds). -In non-SI units, the number of transformations is expressed in microcurie-hours (µCi-hours) and is calculated as 1.44 X initial activity (µCi) in organ X T 112 (hours). -In general, A = 1.44 X A,, X Te, where Ao is the initial activity in the organ, and Te is the effective half-life. -Cumulative activity data are obtained empirically for each radiopharmaceutical by monitoring the time course of activity. -Cumulative activity values are often different for normal patients and patients with certain diseases. |
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PET scanner, something about LGO/BGO, decay constant
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-The PET scanner consists of a ring of bismuth germanate (BGO) detectors, cou-
pled to photomultiplier tubes. -Lutetium oxyorthosilicate (LSO) and gadolinium oxyorthosilicate (GSO) are promising inorganic scintillators that may replace BGO. - LSO is twice as fast |
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111. In CR, AEC is set to N; what will happen if its turned to N + 2, keeping all other things constant?
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The H&D curve also sets the allowed range of radiation exposures the screen-film requires for an acceptable image. Too low of an exposure will result in an image that is light in gray values and will also exhibit excessive noise (or quantum mottle). This region of the H&D curve is referred to as the toe of the curve. Too high an exposure results in images being too dark and is near the shoulder of the H&D curve. For films exposed near either the toe or shoulder region on the H&D curve, the resulting image contrast will also be poor compared to images with the exposure values in the linear region of the curve
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