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• Users: BobP
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thanks
2. ### KVp and number of x-rays

Why does increasing the kVp in x-ray production increase the number of x-ray photons if the number of electrons produced by the cathode is unchanged? thanks
3. ### I Geometric efficiency and CTDI(vol)

Is there a relationship between the geometric efficiency of the scanner and computer tomography dose index of a scanner? I expect the relationship would be inverse but I wanted to check (i.e: if I half the geometric efficency I would double the CTDI(vol). Is this correct thanks
4. ### B Antiparticle production rule?

Thank you. very detailed answer. very grateful
5. ### A PET scanners -- SNR versus NECR....

Sorry. When I say "basically the same" I mean a high SNR = high NECR... so they are linearly related...but I clarified this issue with my lecturer.. He said PET has a higher SNR and a higher NECR :)
6. ### B Antiparticle production rule?

If I produce an anti-particle (e.g: positron) in a reaction MUST I produce a non-anti particle too (e.g: neutrino)...is this a rule? thanks
7. ### A PET scanners -- SNR versus NECR....

Well my lecturer said that SNR is basically the same as NECR. So it have a lower SNR and a higher NECR :)
8. ### Frequency of RF pulse in MRI

My question was based on a misunderstanding of the difference between frequency of the RF pulse and Larmor frequency. I foolishky assumed they were the same which is why I was confused. However problem is now fixed :) Thanks for your help though :)
9. ### A PET scanners -- SNR versus NECR....

The NEC is the true count rate of a theoretical image without any scatter or random events which would give the same statistical quality image as a real image which includes scatter and randoms.
10. ### Frequency of RF pulse in MRI

The magnetic moment of protons precesses at a frequency ω0=γB0 about the static magnetic field. In order to move the magnetisation vector into the transverse plane the RF pulse must be applied at a frequency ω0. However, as B1 (the field strength of the RF pulse) is << B1 how is this possible...
11. ### A PET scanners -- SNR versus NECR....

Not according to my lecturer...
12. ### A PET scanners -- SNR versus NECR....

In PET, 2D PET scanners have a superior SNR to 3D PET scanners as the influence of scatter and random events is lowered by the septa between detector rings. However, the NECR (noise-equivalent count rate), which is linearly proportional to SNR, is higher in 3D PET scanners. These two facts seem...
13. ### Signal to noise ratio in a CT scanner

My course is entire lecture-based and we were told we didn't need books. as they are so expensive I didn't buy any. I did a google search but couldn't find anything Having said that I realized I probably got two things in the working the wrong way around but the answer is still N? right...

thanks :)
15. ### X-ray tube output

Thank you for your help :)
16. ### I Fourier transform sum of two images

I see. well thank you for the confirmation but as I have a very limited knowledge of calculus it seems like it'll be a long time before I can prove why the bottom image is correct. Thanks again for your help though :)
17. ### I Fourier transform sum of two images

Hi. Like I said I don't know any of the maths so I am learning everything conceptually. So I don't really know what you mean by 3 delta functions :(
18. ### I Fourier transform sum of two images

Presumably because it is symmetrical about the centre of k-space. But as the image only displays a single frequency I wasn't sure if I only needed to display two conugate pairs or lots By your answer am I correct in assuming you think the bottom image is correct then?
19. ### I Fourier transform sum of two images

Ok, in addition then which of the two examples shown correctly represents the transformation between the spatial domain (right) and domain (left) I am only learning the FT to gain a very crude understanding of how image reconstruction is done. As I do not have a physics background the course...
20. ### I Fourier transform sum of two images

Right and left (referrring to the images)
21. ### X-ray tube output

If I have 900 uGy/sec when I have 80 uGy/mAs and the machine is on for 150ms in total over a 1 second period Then I have 80 * mA per second = 900 Therfore mA = 11.25 mA BUT as the current is not always on the actual mA is mA * 15 * 10 * 10-3 = 11.25 SO Answer = 75 mA But for part (ii) If...
22. ### I Fourier transform sum of two images

I thought the FT was about decomposing images into different frequencies. So I was showing the inverse of what I thought the FT and asking if it was correct as it was easier for me to show it this way. Is what I showed not related?
23. ### I Fourier transform sum of two images

The FT decomposes images into its individual frequency components In its absolute crudest form, would the sum of these two images (R) give the L image?
24. ### Signal to noise ratio in a CT scanner

Homework Statement If the relative noise (noise divided by signal) in a region of a CT slice is measured to be N what would be the value if the tube current was halved, the pitch increased from 0.9 to 1.2, the rotation time increased from 0.75s to 1s and the slice width increased from 1mm to...
25. ### X-ray tube output

Homework Statement (The question is in the image attached) (c) An X-ray unit in the cardiac catheter labs has an output of 80µGy/mAs at 1 meter when the unit is set at 100 kVp. After adding 0.3mm Cu to the beam the photon intensity is reduced to a quarter and tends to vary in proportion to...
26. ### X-ray beam filtering

Well exactly. if we consider the brehmsstrahlung radiation, the probability of absorption is less than k-edge x-rays so they should be absorbed less? no? hence the k-edge x-rays are absorbed MORE than the other radiation?
27. ### X-ray beam filtering

In mammography, an Mo anode is used because it produces characteristic X-rays at about 17-20 keV. Apparently, the ideal filter is also Mo. Why is this? Surely all the x-rays would just be re-absorbed by the filter? Thank you
28. ### Small focal spot in X-ray imaging

Thanks :) I will do
29. ### Small focal spot in X-ray imaging

I''ve attached the only diagram from our notes. This question was not covered by my course at all which is why I am confused about its presence in a past exam
30. ### Small focal spot in X-ray imaging

The question was in a past exam paper and the first part asked me to draw the design of an x-ray system. no other context unfortunatley
31. ### Small focal spot in X-ray imaging

Yes. That is what I meant. Sorry for the confusion I've been reading that x-ray filament size also has an affect but not sure how. do you know anything about this?
32. ### Small focal spot in X-ray imaging

It does. but doesn't that reduce focus spot size?
33. ### Small focal spot in X-ray imaging

Unfortunatley I cannot post this question in the Homework section (not sure why) so I hope its OK if I post here and show work as appropriate < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > QUESTRION State two design features in an X-ray tube...
34. ### SNR in X-ray imaging

Homework Statement (1) An ideal digital detector only suffers from quantum noise. If, after being exposed to 5 µGy the mean pixel value in the image is 100 and the standard deviation of the pixel values in the image is 5, calculate the SNR? The relationship between pixel value and detector...
35. ### Ultrasound - Doppler angle vs. beam steering angle

In ultrasound what is the difference between beam steering angle and Doppler angle thanks

Thank you
37. ### PET imaging resolution

Seems so obvious now you say it! thanks so much
38. ### PET imaging resolution

Hi, my lecturer said that in PET imaging, the image resolution is superior when the E(max) of the positrons is lower. Why should this be? Thanks

Hi, I am slightly confused about the causes of spectral broadening and reverse flow in duplex ultrasound so wanted to clarify if I am correct. Here is my understanding. Is it correct? - Spectral broadening typically occurs in areas of parabolic laminar flow, distrurbed flow or turbulent flow...
40. ### MR spectroscopy J-coupling phase

My lecturer said the following: (see uploaded image) However the two statements are not the same, which is correct? thanks

42. ### Basic fluid energy

d Fingers crossed it will make sense in the exam!
43. ### Basic fluid energy

Ok, so in an examination how do I know which to use? PS I am studying haemodynamics (energy of blood in the body)
44. ### Basic fluid energy

In fluid dynamics, the total energy of a fluid can be given as: Pressure energy + gravitational potential energy + KE or P + ρgh + ½ρ(v^2) But I have also seen the expression P - ρgh + ½ρ(v^2) NOTE the minus sign in the second equation. Which is correct? Why are both equations used Thank you

thanks
46. ### NMR spectroscopy question

thank you. To clarify, did you mean However, the J-coupling comes from spin-spin interaction, which is DEPENDANT on B0.
47. ### NMR spectroscopy question

I see. thanks
48. ### NMR spectroscopy question

Ah of course! thanks On a slightly unrelated note, I have been told that the separation of J-coupled peaks increases as B0 increases. Please could you suggest why this is, again, as ppm is unrelated to B0
49. ### NMR spectroscopy question

Why does SNR increase with B0? thanks Sadly not :( Is it possible to explain why it is more complicated without going into it?
50. ### NMR spectroscopy question

Thanks. Why does resolution increase? Has it anything to do with a longer FID decay time? If so, how does this happen? Don't think so. I am talking about acquiring a signal from a specific voxel in the brain, for example, using spectroscopy in a clinical setting. My lecturer said we cannot use...
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