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  • Less pain, less radiation in breast cancer detection

Nov 2008
Amanda D. Francoeur,

A high-contrast x-ray technology could replace existing painful mammograms in clinical practice and in detecting breast cancer at an earlier stage. Compared with current x-ray technologies, the method uses low radiation doses and provides clearer imaging that enables detection of small lesions even in dense breast tissue.

“The ultimate goal of [the new technology] is its use in high-resolution, low-dose in vivo breast CT, which could provide more accurate morphologic information for detection, localization and classification of diseases,” said lead researcher Jani Keyriläinen of Turku University Central Hospital in Finland. Keyriläinen and fellow researchers in Finland, Germany and France conducted a study comparing the new technology, analyzer-based x-ray imaging computed tomography (ABI-CT), with current clinical methods.

ABI-CT offers high spatial resolution, yielding 3-D images of the entire breast that are considerably clearer than mammography x-rays. The technique exposes tissue to a dose of only 1.9 mGy (30 keV) of radiation as opposed to 0.9 mGy for single-view mammography. Malignant and benign calcifications – mineral buildup that can signify cancer – are detected even in the densest adipose and glandular tissue, which previously could have been seen only under a microscope. “ABI-CT has the advantage of nondestructively obtaining 3-D microscale information on object structures,” Keyriläinen said.

ABI-CT vs. primary x-ray techniques

Using diagnostic mammography, x-ray CT and the new technology, the researchers observed breast tissue invaded with lobular carcinoma, the second most common breast cancer type. Each method collected shape, density and border characteristics of the calcifications. This type of diseased tissue was chosen because it is hard to diagnose with x-ray mammography and ultrasonography. Histopathology confirmed the researchers’ findings.

With planar x-ray mammography, the standard diagnostic method, patients undergo painful compression of the breast to minimize thickness of overlapping tissue and to prevent movement, so that images are sharp. However, lack of contrast renders 10 to 20 percent of lesions unidentified. This method also requires multiple scans, exposing the patient to more radiation; with thick objects, identifying diseased and healthy tissue is difficult, so only dense calcifications are identified.

A specimen with lobular carcinoma is viewed by x-ray CT (left). Low spatial resolution severely hinders visibility and, as a result, thick tissue hides cancerous lesions. The same specimen is viewed with the new analyzer-based x-ray CT method (right). Dark adipose and glandular tissues, along with lesions, are clearly distinguishable. The new technology may detect cancer earlier than previous methods. Courtesy of Radiology.

Visualization of lesions is limited also with x-ray CT. Although the method provides high-contrast imaging, its spatial resolution is low, enabling detection in only the thickest tissue. Other drawbacks of the method are that soft breast tissue is exposed to much higher amounts of radiation – 6.9 mGy – and that injection of a contrast medium is required for in vivo imaging.

In contrast, the new technology features high-resolution volumetric imaging, so there is no need for compressing breast tissue. In addition, 3-D imaging capability utilizes attenuation, refraction and scatter rejection to identify shapes and margins more accurately, so more calcifications are visible. In the study, dark adipose tissue was distinguishable from glandular tissue, and the thinnest collagen strands could be recognized. ABI-CT is a superior technique because it can detect less obvious breast cancer anomalies, even in dense breasts.

According to the researchers, their next step is to lower the new technology’s radiation dose even more. “We wish to continue developing the technique, by further reducing the dose for one CT,” said team member Alberto Bravin. “It seems that the dose of ABI-CT can be reduced relatively easily by a factor of 3 to 5, by improving the data acquisition,” Bravin said.

To incorporate the new technology into clinical practice, the investigators will compare ABI-CT with other upcoming developments. “We wish to compare ABI with other x-ray phase contrast techniques to see which is the most suitable for a clinical implementation at intense compact x-ray sources presently under development around the world.”

Radiology, October 2008, pp. 321-327.

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