Design and Implementation of a Compact Low-Dose Diffraction Enhanced Medical Imaging System

Rationale and Objectives

Diffraction-enhanced imaging (DEI) is a new x-ray imaging modality that differs from conventional radiography in its use of three physical mechanisms to generate contrast. DEI is able to generate contrast from x-ray absorption, refraction, and ultra-small-angle scatter rejection (extinction) to produce high-contrast images with a much lower radiation dose compared to conventional radiography.

Materials and Methods

A prototype DEI system was constructed using a 1-kW tungsten x-ray tube and a single silicon monochromator and analyzer crystal. The monochromator crystal was aligned to reflect the combined Kα1 (59.32 keV) and Kα2 (57.98 keV) characteristic emission lines of tungsten using a tube voltage of 160 kV. System performance and demonstration of contrast were evaluated using a nylon monofilament refraction phantom, full-thickness breast specimens, a human thumb, and a live mouse.

Results

Images acquired using this system successfully demonstrated all three DEI contrast mechanisms. Flux measurements acquired using this 1-kW prototype system demonstrated that this design can be scaled to use a more powerful 60-kW x-ray tube to generate similar images with an image time of approximately 30 seconds. This single–crystal pair design can be further modified to allow for an array of crystals to reduce clinical image times to <3 seconds.

Conclusions

This paper describes the design, construction, and performance of a new DEI system using a commercially available tungsten anode x-ray tube and includes the first high-quality low-dose diffraction-enhanced images of full-thickness human tissue specimens.

Since Roentgen’s discovery in 1895, x-ray imaging has relied on the varied attenuation of photons to generate images. Diffraction-enhanced imaging (DEI) is a new x-ray imaging modality that uses two additional contrast mechanisms, refraction and ultra-small-angle scatter rejection (extinction) . Previous imaging of breast cancer specimens , articular cartilage , and small animals with synchrotron-based DEI systems has shown improvement in fine detail in images compared to conventional radiography, with applications ranging from industrial inspection to medical imaging .

In conventional radiography, contrast between different tissues is provided by their differential x-ray attenuation. For soft tissues, with adjacent materials having similar electron densities, achieving adequate contrast with conventional x-ray imaging requires imaging at low x-ray energies (approximately 20 keV) to take maximal advantage of small differences in the effective atomic number through the photoelectric effect. Unfortunately, the attenuation of x-rays increases as energy is lowered. To obtain adequate transmission through the body and produce an image with an acceptable signal-to-noise ratio, more incident radiation must be used when imaging at low energies, resulting in a higher absorbed dose to patients.

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Materials and methods

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$Figure 1, X-ray tube–based diffraction-enhanced imaging prototype design schematic.$

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Results

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$Figure 2, Nylon refraction phantom and measured postanalyzer rocking curves. The diameters of the nylon monofilaments from largest to smallest are 560, 360, 200, and 100 μm. Phantom images were acquired at −0.6 microradians (a) and +0.6 microradians (c) on the rocking curve using a tube voltage of 160 kV and 6.2 mA with a surface dose of 0.04 mGy. A measured postanalyzer rocking curve (b) using the Bragg [111] and Bragg [333] reflections is presented to demonstrate system performance.$

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$Figure 4, Full-thickness breast specimen image acquired using a GE Senographe 2000D (GE, Paris, France) conventional digital mammographic system (a) and a corresponding image acquired using the compact diffraction-enhanced imaging system (b) . The 12.0-cm-thick specimen containing an invasive cancer was compressed to 7.0 cm and mounted to provide a mediolateral view of the breast. Each image was acquired using a tube voltage of 160 kV and 6.2 mA with a surface dose of 0.04 mGy and an absorbed dose 0.035 mGy. The spiculated masses and skin evident in the conventional digital radiograph are visible in the diffraction image.$

$Figure 5, A human thumb image acquired using the compact-source diffraction system. Note the soft-tissue detail, including the tendon with its attachment to the bone, the fingernail, and the interface of the skin edge and subcutaneous tissue. An area of five small soft-tissue calcifications is identified in the image by an arrow .$

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Discussion

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Conclusion

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Acknowledgments

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Design and Implementation of a Compact Low-Dose Diffraction Enhanced Medical Imaging System

Rationale and Objectives

Materials and Methods

Results

Conclusions

Materials and methods

Results

Discussion

Conclusion

Acknowledgments

References

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