Why SPECT produces images with higher contrast

[nousername]

Homework Statement

Why does SPECT produce images with higher contrast compared with its alternatives such as PET?

The Attempt at a Solution

I HAVE NO IDEA! I honestly researched everywhere, they only say that it has a higher contrast. I think its something to do with the hardness (penetrating power) of the gamma rays but that doesn't make sense.

Can someone please help me as i am doing some research for some assignment and i need it ASAP. Thanks.

 

[davo789]

Think about how they both work. If you describe briefly how they both work here then I can try and nudge you in the right direction :)

 

[nousername]

Well with spect radionuclides decay and emit single gamma ray photons and which is then detected by a gamma ray camera. PET works similarly but with two gamma ray photons, but that can't be what results in a higher contrast right? I thought the emission of more gamma ray photons resulted in a higher resolution image. But that's as far as i know.

 

[davo789]

By which process are the gamma rays (in PET) created? And how does this affect its resolution?

 

[nousername]

Ok, took some time to find out, but here we go. In PET, a nuclei decays to produce a positron (Beta plus decay) and this positron then collides with an electron and they annihalate each other (no idea why) to release two gamma ray photons in opposite directions. Because there are two gamma rays emitted, the you have two sources from the same spot and hence the gamma camera can make a clearer image. Is this right so far?

 

[danielakkerma]

You're absolutely right, but you must consider this:
The contrast of any such image is formed by the ratio of a region which is translucent, or diaphanous to the gamma rays to a region impregnable/impassable by them, say, osseous tissue.
The presence of TWO photons(in PET scans), helps greatly with the establishment of the location of annihilation of electrons/positrons, resulting in greater resolution capacity, but muddles the image in terms of contrast, because, and this is the thing to remember, that the positron may still travel a distance Before it annihilates, often skewing the image, in a practicular region, to a degree of a few micrometeres, ultimately, amounting to centimeteres.
Contrary to this, SPECTs produce a single photon, directly from the "source", and although they make for more difficult pin-pointing(using Radon transforms), their passage/blockage is directly depicted because they emanate from the specific area being imaged.
I hope that clears things up,
Daniel

 

[nousername]

ohhhhh, so because two gamma rays are emitted in PET it has higher resolution but since the gamma rays don't come directly from the source it has a lower contrast?

 

[danielakkerma]

Yes!
And as a result, several regions may thus overlap.
PETs are much more useful, say, in oncology, where diffusion patterns, uptake, and migration patterns of soft tissues are important(like tumor cells and what not).
SPECTs, which are cheaper, and quicker to obtain, are used primarily for nontranslational tissues, such as bone, and non-metastatasis brain scans and so forth...
Daniel

 

[davo789]

danielakkerma, you got there before me!

 

[danielakkerma]

Glad to be of use!
Better luck next time :),
Daniel

 

[nousername]

hahaha lol, bad luck davo, thanks to both of you. see you around (in the forums lol)