MRI vs Color X-Ray Technology: What Are the Differences and Benefits?

[artis]

Today I read about a seemingly new way of using Xrays that results in images that can be colored and more detailed.

https://www.marsbioimaging.com/mars/

See this link for example.
I do wonder what would be the major differences or benefits from such technology given modern MRI also has very high resolution.
Is it that the X ray imaging is faster and less complicated so can be used on some real time applications for security like airport luggage etc?

 

[sophiecentaur]

Today I read about a seemingly new way of using Xrays that results in images that can be colored and more detailed.

https://www.marsbioimaging.com/mars/

See this link for example.
I do wonder what would be the major differences or benefits from such technology given modern MRI also has very high resolution.
Is it that the X ray imaging is faster and less complicated so can be used on some real time applications for security like airport luggage etc?

CT scans have three dimensional density information. Apart from it being great to use, I cannot see how MARS does anything revolutionary by using false colour. Having said that, the basic algorithms for getting 3D information from a cylindrical or spherical scan of an object are very clever and will have helped a lot in diagnosis of almost anything inside a body. Displaying information understandably is also very useful.

 

[A.T.]

CT scans have three dimensional density information.

This sounds like they analyse the frequency of the passing x-rays:

Color x-ray is where the energy (or color) of the x-rays that pass through the object is measured.

Traditional x-ray measures the number of x-rays that have passed through, which gives information about the density of the object. Very dense materials don’t let many x-rays through, less dense objects let more through. Color x-ray can give information about which material an x-ray passed through rather than just its density. That means two objects of similar density but different materials can be distinguished.

 

[cosmik debris]

The Mars thing was developed at the University I work at. One of the big advantages of this technology is cost. A CT scanner is much cheaper to build than an MRI and could benefit poorer countries.

Cheers

 

[gleem]

First the MARS instrument is a micro CT meaning it can only scan relatively small objects. Its scanning volume is a maximum of 100 mm diam by 280 mm length so human imaging is out. For conventional CT depending on physical density and chemical composition different tissues can be represented by same or nearly the same shade of gray making them difficult to differentiate. The MARS system uses several different x-ray energies and determines a more unique absorption profile for different tissues or other materials that are of interest. So instead of having images with 32 shades of gray, which is about the max the human eye can distinguish like the traditional CT produces, the color schemes can dramatically show small but significant differences in tissue that might have gone unnoticed with a gray scale image.

Now there are dual energy CT scanners for human scanning that are currently being produces but may not be as sensitive to the tissue difference like the MARS system but still better than single energy x-ray scanners in delineating different substances in the body. Even two energies provide an advantage in distinguishing different substances and provide a way of using new materials that will be useful in diagnosis of disease like materials that concentrate preferentially in certain tissues.

 

[artis]

Ok so far from your posts my basic conclusions would be that the color x ray is not that better than a MRI already is but it's cheaper and simpler?

Then there is a question, why the size limit of the scanning object is so small, is there any physics that determines this or is it just a scale thing for a test prototype?As for the ordinary x ray images and the limit of the human eye for shades of grey I think this might get solved in the very near future with specific AI (not confused with general AI) where we already have software capable of telling each two human faces apart and recognizing face patterns I also read about technology that will be able to take an ordinary X ray and get much much more information out of that single picture as compared to what an average doctor might see in the picture, shouldn't this capability render the color x ray kind of "just another thing" ?

 

[sophiecentaur]

I see. You are suggesting that there’s more than just density information. So the different attenuation for different photon energies gives extra information. That’s good!

 

[A.T.]

instead of having images with 32 shades of gray, which is about the max the human eye can distinguish like the traditional CT produces,

A traditional CT produces at least 16bit images which is 65536 shades of gray, not 32. What the eye can distinguish is not a limiting factor here, because you usually look at CT-imagery using software, which allows you to change the gray value range that you want map on a black to white scale.

the color schemes can dramatically show small but significant differences in tissue that might have gone unnoticed with a gray scale image.

MARS is not about increasing the density resolution, but about adding a different type of information based on frequency.

 

[artis]

so MARS in the end is what MRI is, just with ionizing radiation (X rays of various wavelenghts) ?
Where in a MRI one positions the protons of hydrogen atoms to align with the static high strength field and then different tissue/matter respond differently to the applied multiple wavelength RF field, in MARS as I understand one differentiates between different tissue by blasting them with more than one frequency within the X ray spectrum in the end getting different frequency output?So having two tissue that are of similar density they would seem as one and the same in a regular X ray because regular X ray only counts the intensity of the radiation passing through in each sector but in a "color " X ray two tissue of similar density but each responds/attenuates the passing X rays differently given that both receive at least two different wavelengths instead of a single one, then the software assigns a color based on pre-programmed colors for certain density and type materials.
At least this is what I understood from reading about it.

 

[gleem]

A traditional CT produces at least 16bit images which is 65536 shades of gray, not 32.

I did not imply that a CT scanner can only display 32 shades of gray. TVs and monitor are capable of displaying currently I believe up to 4000 shades of gray. The human eye can only distinguish about 32 distinct shades of gray or brightness levels under given lighting conditions, that is from the bright to black can be divided into some 32 shades of brightness that can be determined to be distinct. This would be similar to saying that the brain digitized its perceived brightness levels at about 5 bits. Check out on the web the Mars contrast test chart which show letters of different shades of gray with a brightness range of 100:1 in equal decrease in brightness. There are 40 letters. Note the contrast between adjacent letters and tell me how conspicuously different they are.

What the eye can distinguish is not a limiting factor here, because you usually look at CT-imagery using software, which allows you to change the gray value range that you want map on a black to white scale.

In CT imaging what is determined is the relative attenuation of the tissue as determined by CT number which is normalized to water which is set to zero. This normalization of CT numbers is referred to as Hounsfield units. Air becomes -1000, Lung about -600, water of course is 0, muscle about 50, bone is about 1800 with all other tissue between these numbers. Other substances particularly with atomic numbers greater than calcium will have HU of higher value. In CT visualization of the data(HU) depending on what part of the anatomy or pathology that is of interest, a base level for the HU of interest is chosen and a range (window) is set to encompass the range of HU that is of interest. The available brightness levels available from the monitor is then spread across the value of HU to be visualized.

MARS is not about increasing the density resolution, but about adding a different type of information based on frequency.

My post did not say that. I specifically referred to density and chemical composition as determining the CT number. CT scanners as well as the MARS instrument can do this. The Mars system can more definitively delineate substances based on composition as well as density.

As for the ordinary x ray images and the limit of the human eye for shades of grey I think this might get solved in the very near future with specific AI (not confused with general AI) where we already have software capable of telling each two human faces apart and recognizing face patterns I also read about technology that will be able to take an ordinary X ray and get much much more information out of that single picture as compared to what an average doctor might see in the picture, shouldn't this capability render the color x ray kind of "just another thing" ?

Yes . AI can look* at the HU (see above) values specifically and tell the difference between two areas which are statistically different but which may not be appreciated by a human looking at a monitor. It can do this without setting specific HU levels and windows (see above). It can also more easily with a patients digital medical record correlated the CT finding with the differential diagnoses and rare conditions not remembered by a human as well as finding incidental conditions not yet clinically manifested (humans do this too but AI could be more sensitive and faster).

* If I were in the business of developing AI for CT this is what I might try.WRT color representation. As I stated above the human eye can only perceive certain differences brightness. Using different colors that range can be applied to as many colors as can be prominently represented. So with red, green, orange and blue you can have a brightness scale for each and thus display four times the information compared to gray scale presentation or you could fold the color together to represent a the different HU in the range more conspicuously.

 

[gleem]

so MARS in the end is what MRI is, just with ionizing radiation (X rays of various wavelenghts) ?

No. MRI determines the concentration of chemical substances or chemical environments by measuring their magnetic moment. It is capable of investigating physiological process as well as morphology ( structure) like CT. Look up nuclear magnetic resonance to understand the physics.

So having two tissue that are of similar density they would seem as one and the same in a regular X ray because regular X ray only counts the intensity of the radiation passing through in each sector but in a "color " X ray two tissue of similar density but each responds/attenuates the passing X rays differently given that both receive at least two different wavelengths instead of a single one, then the software assigns a color based on pre-programmed colors for certain density and type materials.
At least this is what I understood from reading about it.

With CT or plain x-rays it is both density and composition that are important. The use of two or more energies(we like to use energy instead of wavelength when talking about x-rays) density affects attenuation the same for different energies but composition can be markedly different for different energies. Two tissues with different densities and different compositions can have attenuations that are too close to distinguish at one energy. But changing the energy will change the attenuation enough to make the materials discernibly different in the scan.
The use of the MARS system seems to be of particular value for what is known as contrast materials. Materials introduced into the body that have attenuation characteristics that are considerably different from the natural components of the body. So in conventional x-rays or CTs a compound with Iodine is injected into blood to visualize the blood vessels. Iodine has an atomic number 53 or 6.6 time greater than Oxygen. This results in an absorption of certain energy x-rays at a rate thousands of times greater than soft tissue with the same concentration. So even a little Iodine shows up clearly as a lighter area. Using multiple energy x-rays can more easily discern the presence of substances like, zinc, thallium, gold even when used simultaneously. I doubt the MARS system adds much to soft tissue discrimination for human scanning since the energy needed to discriminate oxygen, carbon or nitrogen are way to low for big objects to be penetrated.

 

[sophiecentaur]

So with red, green, orange and blue you can have a brightness scale for each and thus display four times the information

The limit is not in the displayed primaries but with the eye's tristimulus colour analysis. Talking in terms of Colour TV, we need to go to 'millions of colours' if we want to avoid the eye perceiving colour contours on large areas of slightly varying colours. That implies that the gamut of colours that can be perceived in the triangle of the three TV primaries (CIE Colour Chart) would contain 'millions' of just-distinguishable elements. Otoh, the equivalent just-distinguishable steps on a monochrome scale would be about the square root of that - i.e. thousands of shades. Those are ball park figures - more advertising stats but they seriously show the increased resolution of presented data (in analogue form) and, very acceptable to the human brain.

 

[gleem]

No. MRI determines the concentration of chemical substances or chemical environments by measuring their magnetic moment. It is capable of investigating physiological process as well as morphology ( structure) like CT. Look up nuclear magnetic resonance to understand the physics.

My statement of what MRI determines was poorly and hastily made and need greater explanation. The magnetic moment (MM) is not measured but is indeed the focus of the processes . A very simple explanation is as follows. When placed in a magnetic field the MM processes about the field like a top precesses in a gravitational field. The frequency of procession is in the radio wave spectrum and depends on the applied magnetic field strength. An RF pulse is applied at the frequency of rotation to excite the MM to a higher energy state. After the pulse the MM begin to return to their original lower energy state emitting an RF signal which is detected. The MM of hydrogen is generally used for imaging. The rate at which this signal is emitted (relaxation time) depend on the perturbations on the excited MM state due to the physical / chemical environment. The image formed reflects the relaxation time of hydrogen in various materials producing the signal variation. By varying the applied magnetic field in a particular manner relative to the reception of the emitted RF signal the relaxation time in voxels at known locations can be sampled and used to produce the image.