Good Vibrations: Ultrasound Elastography

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In February, France's state-operated agency for the funding of innovation awarded a research-and-development grant worth 8.5 million euros to a European company that wants to validate a new application clinically for the still-nascent modality of ultrasound elastography. In this instance, elastography would be used as a targeting mechanism for the treatment of hyperparathyroidism resulting from a growth on the parathyroid glands.

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Douglas O. Chinn, MD

Conventionally, hyperparathyroid cases in France are treated either surgically or with a protracted regimen of drugs, both of which entail risks to the patients and significant costs to the country's national health care system. With the new elastography application, doctors could gain the ability to detect more precisely the lesion site—as well as the extent and degree of necrosis—so that the growth could be bathed in tissue-destroying, high-intensity, focused ultrasound beams. This outpatient-based alternative appears to be simpler, safer, less invasive, and less expensive, leading to the French government's willingness to underwrite clinical investigations of it.

Making Strides

Meanwhile, the quest for simpler, safer, more efficacious tools for the detection of other types of tumors drives exploration of ultrasound elastography in the United States. This is an ambition fueled by a small (but growing) body of evidence suggesting that lesions can be characterized more rapidly, and with a higher degree of accuracy, when elastography is incorporated into the routine patient-examination process.

An important characteristic of tissue is its elasticity. Elasticity can be affected by aging or by inflammation; it can also be affected by malignancy. The ability to visualize changes in that elasticity is thus useful in diagnosing cancer, proponents of elastography say.

Hitachi Medical Systems America, Twinsburg, Ohio, is among the ultrasound vendors marketing an elastography application in the United States. The company's signature offering in that segment is known as the Real-time Tissue Elastography (HI-RTE) system. Detection of tumors using HI-RTE is a relatively straightforward process: One simply positions the ultrasound transducer over the tissue targeted for evaluation and gently applies downward pressure to compress it. HI-RTE then measures the amount of strain and calculates relative tissue elasticity, which is displayed as a color overlay on a standard B-mode image. Abnormal tissue is stiffer (or less elastic) than normal tissue; the system gauges the differences and paints the former in blue and the latter in red or green.

HI-RTE is basically an add-on module for the company's HI VISION™ 900 ultrasound platform. It uses what Hitachi calls an Extended Combined Autocorrelation Method, or ECAM, algorithm to produce the elastography image. This algorithm performs a 2D correlation in both axial and lateral directions. Hitachi says that this overcomes the problem of sideslip and improves the accuracy of the strain image.

At the 2008 RSNA meeting in Chicago, Hitachi demonstrated second-generation advances to HI-RTE. Chiefly, these allow more accurate localization and targeting of lesions in more locations, including thyroid, breast, colorectal, pancreatic, and musculoskeletal structures. In addition to greater accuracy, the showcased improvements also promise faster and easier quantifying of the relative differences in stiffness between a suspicious mass and the surrounding tissue, with the intent being to reduce the need for more burdensome forms of examination.

Prostate Imaging

Among the more interesting recent applications of elastography is prostate cancer detection. Douglas O. Chinn, MD, a partner in Chinn & Chinn Urology of Arcadia, Calif, has embraced elastography for precisely that purpose.

"In my field, there is a paucity of imaging processes that can reliably diagnose prostate cancer," Chinn says. "As a result, we have traditionally been obliged to biopsy tissue in order to make our diagnoses. CT scans, contrast-enhanced MRI, 1.5T and 3T coils, and spectral MRI: They all claim to detect prostate cancer reliably, but the fact of the matter is that they don't. Elastography, however, seems to be different, and it may be more specific."

Chinn reports that researchers are now learning that elastography may also increase the ability to identify malignancies in tissues that are not even suspect. "It's conceivable that elastography will improve our watchful