Optimization of a dual-energy contrast-enhanced technique for a photon-counting digital breast tomosynthesis system: II. An experimental validation.

Carton AK, Ullberg C, Maidment AD.

Source

University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.

Abstract

PURPOSE:

Previously, the authors developed a dual-energy (DE) acquisition technique for a photon-counting digital breast tomosynthesis (DBT) imaging system. Low-energy (LE) and high-energy (HE) images are acquired in a single scan by covering alternate slits of a multislit prepatient collimator with Sn and Cu, respectively. A theoretical model was used to optimize the technique. In this article, an experimental validation of this technique is presented.

METHODS:

Experiments were performed on a prototype DBT system. LE and HE projection images were acquired sequentially; either a Sn or a Cu filter was positioned in the filter holder at the exit window of the x-ray tube. Sn filters from 0.113 to 0.242 mm thick and Cu filters from 0.103 to 0.267 mm were used. The images were acquired with a W target at 49 kV. Tomographic images, hereafter referred to as DBT images, were reconstructed using a shift-and-add algorithm. DE-DBT images were obtained by weighted logarithmic subtraction of the LE and HE images. Weighting factors w(t) that optimally cancel breast tissues with two different glandularities were assessed for 20-80 mm thick phantoms with 0%, 50%, and 100% glandularity. The mean and standard deviation in the per-pixel signal intensity (SI) were calculated in the DBT images. These data were used to calculate signal-difference-to-noise ratios (SDNRs) between iodine enhanced and nonenhanced polymethyl methacrylate backgrounds. To illustrate the feasibility of the technique, DE-DBT images of a structured phantom containing iodine disks were assessed. The experimental results were compared against the values obtained from a theoretical model of the imaging system.

RESULTS:

The average difference between theoretical and experimental w(t) was found to range from 8% to 21%. Experimental w(t) values increase with phantom thickness and Cu thickness, depend somewhat on Sn thickness, and vary more as a function of breast composition in thick breasts than in thin breasts. Theoretical and experimental mean and standard deviation in the per-pixel SI differ by -7% to 10% and by -3% to 4%. Theoretical and experimental SDNR values differ, on average, by 1.5%. Iodine concentrations can be predicted from SDNR; the relationship can be accurately fit to a quadratic. In the images of the structured phantom, iodine concentrations of 1 mg/cm2 and larger are discernable.

CONCLUSIONS:

The strong agreement between experimental and theoretical results in this article indicates that the authors' computer model is accurate.

d.d. 2 oktober 2003:

Onderzoekers aan de universiteit van het Colorado Gezondheids wetenschappelijk Centrum in Denver hebben een onderzoek gedaan naar het effect van The dual-energy contrast-enhanced digital subtraction mammography technique , sorry maar weet geen goed woord hiervoor in het Nederlands. In ieder geval wordt via een intraveneuze injectie een stofje ingebracht die het ontstaan van nieuwe bloedvaten, welke altijd gepaard gaan bij het ontstaan van kwaadaardige cellen, doet oplichten op een computerscherm. Het lijkt een beetje op wat ook gebeurt met de radachlorin in een PDT-behandeling, zie andere alternatieven-Radachlorin en uw verhaal Karen bv. , waar na het inspuiten van de radachlorin de meeste tumoren, ook hele kleine oplichten op een computerscherm wanneer belicht met een laserpen. In deze studie werden 26 vrouwen met deze nieuwe techniek gescreend na geinjecteerd te zijn met een contrastvloeistof. Al deze vrouwen hadden een biopt nodig om te checken of ze wel of geen borstkanker hadden. Bij 13 vrouwen lichten alle kwaadaardige beginnende tumoren op en bleek deze techniek ook achteraf exact aan te geven waar de tumoren precies zaten. Ik kan zeggen dat ik bij verschillende mensen het oplichten via de radachlorin heb gezien op een scherm en dat veel indruk op me maakte. Deze nieuwe techniek is volgens de onderzoekers goedkoper en accurater en zal het nog enkele jaren duren voordat deze techniek massaal kan worden toegepast. O.i. een echt interessante ontwikkeling ook omdat veel vrouwen met borstkanker vaak geconfronteerd worden met wel of geen uitzaaiingen en met deze nieuwe techniek lijkt dit gemakkelijker en precieser te diagnosteren.

Contrast mammography reveals hard-to-find cancers
October 2, 2003

OAK BROOK, Ill. A new technique accurately identifies breast cancers that are difficult to detect with conventional mammography, according to a study appearing in the October issue of the journal Radiology.

"The dual-energy contrast-enhanced digital subtraction mammography technique is feasible for hard-to-demonstrate breast cancers and is worthy of further study," said the study's lead author, John M. Lewin, M.D. Dr. Lewin is an associate professor of radiology at the University of Colorado Health Sciences Center in Denver, and director of breast imaging research and co-director of breast imaging at the University of Colorado Hospital Breast Center in Aurora.

Conventional mammography misses 10 percent to 20 percent of breast cancers, including 9 percent of those that can be felt during physical examination.

Dual-energy, contrast-enhanced digital subtraction mammography involves the injection of a contrast agent to highlight new blood vessel development that accompanies malignant growth. Two images are taken at different energy levels and subtracted from one another to disclose the tumor. Similar techniques are being successfully employed in other areas of radiology.

"We expect that dual-energy, contrast-enhanced digital subtraction mammography will become an alternative to breast magnetic resonance imaging (MRI) in evaluating difficult to interpret mammograms or for screening women who have an elevated risk for breast cancer," Dr. Lewin said. "This technique may also be useful for examining breasts of women who have already been diagnosed with one cancer to identify potential undetected malignancies," he added.

For the study, the researchers used dual-energy, contrast-enhanced digital subtraction mammography to evaluate 26 patients whose mammograms or breast exams warranted a biopsy.

"By using a contrast agent with digital mammography, we were able to see cancers that were invisible on conventional mammography. About half of the women in the study had cancer, and this technique lit up all the malignancies," Dr. Lewin said.

Specifically, the researchers found that 13 of the patients had invasive cancers. Eleven of the invasive cancers were strongly enhanced, one showed moderate enhancement and another was weakly enhanced. In another patient, a case of intraductal carcinoma in situ showed a weakly enhanced duct. The 12 benign cases either showed weak enhancement or none at all.

Dr. Lewin said that the new technique is less costly than MRI, which is being used to screen high-risk women. The procedure is similar to conventional mammography with the addition of an intravenous injection.

"This is still a research technique," Dr. Lewin said. "If the results we achieve in further research are as good as what we have so far reported, then I expect this could be clinically available in two to five years."

The University of Colorado Health Sciences Center, the University of California, San Francisco and Brigham and Women's Hospital in Boston are planning a joint clinical trial to study this technique's appropriateness for screening women at very high risk for breast cancer. The trial would begin in October 2004.

Radiological Society of North America