Detection of small low-contrast objects in mammography: effect of viewbox masking and luminance

J Wang 1, J E Gray

Abdelghani Rouini Thank you the article. But I am looking for a study that tells that this material can be used as a low-contrast object. And hopefully, it should be low cost. Gold is not a low-cost material but I think it's a good contrast object.

Thank you anyway.

Dear Neil Madrigal ,

when you are talking about x-ray contrast you have to have two materials in mind, not a single one such as Al or air alone.

I see that in your set up you will have a material which has a quite low contrast with respect to PMMA.

Polymer materials (plastic) has a quite similar elemental compositions and thus have a quite similar x-ray mass-attenuation coefficient µ/ rho.

The x-ray attenuation coefficient µ itself is calculated by µ= (µ/rho)*rho , so the x-ray contrast mainly depends on its density rho for these materials.

In your case you should look for plastic materials having densities quite close to that of PMMA ( rho~1,18g/cm³).

Here are some suggestions:

PA6: rho ~ 1,12 g/cm³

PA12G; rho ~ 1,03 g/cm³

PC: rho ~ 1,2 to 1,22 g/cm³

PS: rho ~1,05 g/cm³

You may search for other materials by yourself.

Good luck and best regards

G.M.

Remarks:

a) Aluminium has a quite high atomic number compared to the mean Z of PMMA and thus has a much higher x-ray mass attenuation coeffcient. Furthermore its density is about two times larger than that of PMMA. You will have a large contrast when combining Al and PMMA (at same path lengths).

b) In the case of air your will have a quite similar mean atomic number with respect to PMMA and thus the x-ray mass-attenuation coefficients will be similar. But the densities are quite different; so you will have a large -x-ray contrast between air air and PMMA (at same path lengths).

Gerhard Martens Thank you for your insightful response!

Where did you get the rho values of the materials that you recommended to me? Do you have a reference?

I get your point that if I set up a low contrast performance, I should consider 2 objects that have slight differences in attenuation. I am just confused on why gold is applicable and suggested as a low-contrast material. It is like a number 1 material if you are going to build a test device for mammography. But has a large different attenuation than PMMA and Aluminum. Because sometimes the background block of gold is made of either PMMA or Aluminum. Aluminum is also a suggested material for low contrast tests for the radiography X-ray machine. So are aluminum and air not valid for a low contrast test?

Dear Neil Madrigal ,

thanks for feedback...

With respect of the ability to take Al or even Au ( or even air) as 'low contrast' material depends on how you will set up your phantom.

My suggestions above are based on a set of blocks of equal thickness(es).

But your proposal above of using blocks of different thicknesses is based on the idea of step or stair phantoms. Here you can use thin layers of Al or even Au to have low additional x-ray attenuation. So also here you can use rather high Z elements for producing low contrast. The layer thickness is here the variable, by which the desired contrast is adjustable.

Even a set of PMMA blocks of slightly different heights will give you a series of fine tuned contrasts in your set up, without the necessity of Al or Au layers on top or beneath them.

With respect to the density values of plastic material I have no literature quickly at hand now. But please 'google' for data sheets of such materials. The density is written down there.

See for example:

https://www.kern.de/de/technische-datenblaetter-kunststoffe?lng=2

General remark:

Please pay attention that the x-ray attenuation coefficient µ is dependent on the x-ray photon energy E in use : µ=µ(E). So any contrast will depend on the spectral distribution I(E) of the output of your x-ray source, which is mainly governed by the filtration and the kVp setting of the tube.

So when changing the tube voltage the contrasts change a bit.

Gerhard Martens Thank you so much for entertaining my question! I really appreciate it.

Actually, the block of PMMA I am going to use has a thickness of 45 mm and for my low contrast material, I am thinking of aluminum to have 0.01 to 0.10 mm thickness or air to have 0.1 to 0.5 mm depth. Those are just my top 2 options. But I am still looking for different low-contrast materials other than those. I am going to consider the different plastics that you suggested. Thank you very much!

Look into contrast detail phantoms