Preliminary study on extremely small angle x-ray scatter imaging with synchrotron radiation.

Among the medical physics community, there is nowadays a great interest in the possible implementation of scatter imaging techniques, especially in the field of breast imaging. It is well known that malignant lesions and normal tissue differ in their scattering signatures, and thus scattered radiation can provide a powerful tool to distinguish between the two cases. Up to now, most of the proposed techniques rely on the detection of radiation scattered at angles of the order of a few degrees, which in most cases results in very high contrast values. On the other hand, at those relatively large angles the scattered flux is relatively low with respect to the primary, which often implies the necessity of increasing the dose delivered to the sample in order to achieve sufficient statistics. Furthermore, most of these techniques are based on pencil beam set-ups, which results in an increase of the overall duration of the examination. We propose here an alternative approach based on the detection of radiation scattered at extremely small angles, of the order of approximately 100-200 microrad. This results in a relatively high scattered flux (5-10% of the primary) and in the possibility of utilizing a fan beam geometry, which reduces the acquisition times with respect to pencil beam set-ups. Images of several samples have been acquired, demonstrating that the proposed technique results in an increased contrast with respect to absorption imaging. Possible in vivo implementations of the technique at no dose expense are finally discussed.

An innovative digital imaging set-up allowing a low-dose approach to phase contrast applications in the medical field.

Recently, new imaging modalities based on the detection of weak phase perturbations effects, among which are phase contrast and diffraction imaging, have been developed by several researchers. Due to their high sensitivity to weakly absorbing details, these techniques seem to be very promising for applications in the medical field. On the other hand, digital radiology is undergoing a wide diffusion, and its benefits are presently very well understood. Up to now, however, the strong pixel size constraints associated with phase contrast pattern detection limited the possibility of exploiting the advantages of phase contrast in digital radiology applications. In this paper, an innovative setup capable of removing the pixel size constraints, and thus opening the way to low dose digital phase contrast imaging, is described. Furthermore, we introduce an imaging technique based on the detection of radiation scattered at small angles: the information extracted from the sample is increased at no dose expense. We believe that several radiological fields, mammography being the first important example, may benefit from the herein described innovative imaging techniques.

Experimental evaluation of a simple algorithm to enhance the spatial resolution in scanned radiographic systems.

In order to ensure an early diagnosis of breast cancer, an imaging system must fulfil extremely stringent requirements in terms of dynamic range, contrast resolution and spatial resolution. Furthermore, in order to reduce the dose delivered to the patient, a high efficiency of the detector device should be provided. In this paper the SYRMEP/FRONTRAD (SYnchrotron Radiation for MEdical Physics/FRONTier RADiology) mammography project, based on synchroton radiation and a novel solid state pixel detector, is briefly described. Particular relevance is given to the fact that the radiographic image is obtained by means of a scanning technique, which allows the possibility of utilizing a scanning step smaller than the pixel size. With this procedure, a convolution between the real image and the detector point spread function (PSF) is actually acquired: by carefully measuring the detector PSF, it is possible to apply a post-processing procedure (filtered deconvolution), which reconstructs images with enhanced spatial resolution. The image acquisition modality and the deconvolution algorithm are herein described, and some test object images, with spatial resolution enhanced by means of the filtered deconvolution procedure, are presented. As discussed in detail in this paper, this procedure allows us to obtain a spatial resolution determined by the scanning step, rather than by the pixel size.

Mammography with synchrotron radiation: phase-detection techniques.

The authors evaluated the effect on mammographic examinations of the use of synchrotron radiation to detect phase-perturbation effects, which are higher than absorption effects for soft tissue in the energy range of 15-25 keV. Detection of phase-perturbation effects was possible because of the high degree of coherence of synchrotron radiation sources. Synchrotron radiation images were obtained of a mammographic phantom and in vitro breast tissue specimens and compared with conventional mammographic studies. On the basis of grades assigned by three reviewers, image quality of the former was considerably higher, and the delivered dose was fully compatible.

Low-dose phase contrast x-ray medical imaging.

Phase contrast x-ray imaging is a powerful technique for the detection of low-contrast details in weakly absorbing objects. This method is of possible relevance in the field of diagnostic radiology. In fact, imaging low-contrast details within soft tissue does not give satisfactory results in conventional x-ray absorption radiology, mammography being a typical example. Nevertheless, up to now all applications of the phase contrast technique, carried out on thin samples, have required radiation doses substantially higher than those delivered in conventional radiological examinations. To demonstrate the applicability of the method to mammography we produced phase contrast images of objects a few centimetres thick while delivering radiation doses lower than or comparable to doses needed in standard mammographic examinations (typically approximately 1 mGy mean glandular dose (MGD)). We show images of a custom mammographic phantom and of two specimens of human breast tissue obtained at the SYRMEP bending magnet beamline at Elettra, the Trieste synchrotron radiation facility. The introduction of an intensifier screen enabled us to obtain phase contrast images of these thick samples with radiation doses comparable to those used in mammography. Low absorbing details such as 50 microm thick nylon wires or thin calcium deposits (approximately 50 microm) within breast tissue, invisible with conventional techniques, are detected by means of the proposed method. We also find that the use of a bending magnet radiation source relaxes the previously reported requirements on source size for phase contrast imaging. Finally, the consistency of the results has been checked by theoretical simulations carried out for the purposes of this experiment.

Mammography of a phantom and breast tissue with synchrotron radiation and a linear-array silicon detector.

A linear-array, silicon pixel detector, capable of counting single photons, was applied to mammography by using a synchrotron radiation beam. Images were obtained of both a mammographic phantom and a breast-tissue sample. The phantom image was acquired with a mean glandular dose of 0.32 mGy. This detector combined with a synchrotron radiation beam allows acquisition of high-contrast, low-dose images of soft tissues.

A linear array silicon pixel detector: images of a mammographic test object and evaluation of delivered doses.

We present images of a mammographic test object obtained using a linear array silicon pixel detector capable of single-photon counting. The detector pixel size was 200 x 300 microns2 and images were acquired by scanning the test object between the laminar detector and the x-ray source with a scanning step of 100 microns. A molybdenum anode tube was used with two different filtrations: 2 mm aluminium and 25 microns molybdenum. Conventional film-screen images were also obtained in order to compare spatial and contrast resolution. In our digital images it is possible to recognize low-contrast details having dimensions smaller than or equal to the dimensions of details visible by means of a clinical mammographic unit. The detection of microcalcifications smaller than 150 microns was possible only when using the Mo filtration. However a copper wire of 50 microns diameter was detectable when embedded in a simulated tissue. We discuss in detail the mean glandular doses (MGDs) delivered during the image acquisition. The MGDs necessary to obtain good-quality images are always smaller than at a conventional mammographic unit. Since MGDs depend on the x-ray spectrum, the dose reduction becomes larger when the applied spectrum is harder than in film-screen acquisition (Al filtration and 35 kVp).