Yuichi Hosoi

Mammographic imaging properties of an experimental SrFBr:Eu 2+ imaging plate

Computed radiography (CR) utilizing imaging plates (IPs), which consist of a photostimulable BaFX:Eu2+(X equals Cl,Br) phosphor, has found wide clinical use. In the present paper, a photostimulable SrFBr:Eu2+ (SFB) phosphor, as well as an IP employing this phosphor (SFB-IP), are experimentally prepared. A test apparatus for reading the SFB-IP is constructed, and the imaging characteristics are evaluated. The x ray imaging characteristics of the SFB-IP are different from those of the BFB-IP (the IP which consists of BaFBr:Eu2+). The difference is due to their x-ray energy absorption coefficients. Under the mammographic exposure conditions, the measurements of noise equivalent quanta as well as the visual evaluation of phantom images reveal that the SFB-IP and BFB-IP have the same quality level of imaging in spite of the PSL intensity of SFB being lower than that of BFB. However, for practical use, many problems are left on the SFB-IP and its reading apparatus.

Analysis of the noise components of the various imaging plates

We analyzed the relationship between the noise components and detectability of the various Imaging Plates to find the essential factors for improving Imaging Plate. CR system noise is classified into quantum noise and fixed noise. The dominant component of fixed noise is the structural noise of IP. The contribution of the structural noise was relatively high at higher exposure and at higher spatial frequency. For example the ratio of structural noise of early type of IP is 55% in case of 2 mR (5.16 × 10-7 C/kg) exposure at 2 cycles/mm spatial frequency. On the other hand, the ratio of the latest type is about 20%. This improvement leads to 2.3 times NEQ combined with improvement of quantum noise. Threshold depth of the 0.5 mm diameter hole of CD diagram was improved from 1.4 mm to 0.8 mm according to the improvement of NEQ from 50,000 to 100,000 /mm2 at the related spatial frequencies. Amount of improvement of threshold contrast was influenced especially by the NEQ at relatively high spatial frequencies. So improvement of the structural noise, which is dominant at higher frequency, is important as well as quantum noise.