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
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
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 :)
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 :)
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.
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...
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...
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...
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 :)
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?
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...
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...
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?
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?
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...
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...
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?
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
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
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?
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...
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...
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...
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
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
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...