"During mammograms most women are too busy gritting their teeth to ponder the fact that even when squashed a breast has a lot of overlapping tissue that can conceal a cancer. Scientists however have spent decades trying to overcome this inherent problem of breast Xrays. Now theyve found a way. The latest technology makes a threedimensional reconstruction of the inside of the breast. While spatial detail is like a CT scan the radiation dose is the same as with a regular mammogram. The U.S. Food and Drug Administration last month approved the first breast tomosynthesis system tomo is Greek for slice. In studies it enabled radiologists to find more malignancies with fewer false alarms or false positives. The new system is made by Hologic Inc. of Bedford Mass. but other companies notably GE Healthcare and Siemens are racing to bring their own versions to market. No one is ready to say tomosynthesis will end the long debate over the benefits and risks of breast cancer screening. The advance will not necessarily solve the dilemma of overdiagnosing and overtreating tiny early malignancies that may never progress. And studies show that D mammograms like D ones are only as good as the radiologists who interpret them. Still experts who tested Hologics system are enthusiastic. I definitely can say it depicts the cancer better said radiologist Debra Copit director of breast imaging at Albert Einstein Medical Center in Philadelphia which will soon use it on eligible screening patients. We can see the tumors more clearly.  Mammography introduced in the s is based on the principle that different structures block Xrays to varying degrees so they appear on an image as white gray or black. The ability to uncover cancer before it becomes a palpable lump has contributed to the steady increase in incidence between  and  the number of diagnoses per  women grew from  to . On the other hand early detection combined with better care has cut the death rate over the same period from  to  per  women. But Xrays are imperfect. None of the soft tissues in the breast block Xrays very well and the central part blocks more rays simply because it has more tissue. Radiologists say this makes searching for cancer on a mammogram sort of like hunting for a snowball in a blizzard especially if the breast tissue is dense  as it usually is in premenopausal women. A decade ago mammography took a leap forward when traditional film Xrays gave way to digital formats which can be adjusted to change magnification contrast and other aspects. This has not only reduced radiation doses but also improved accuracy in screening dense breasts studies show. More than  percent of U.S. mammography centers are now digital records show. Still if a tiny tumor is deep inside a breast digital mammography cannot see through the tissue above and below it  the tissueoverlap problem. Radiologists get two mammogram images per breast taken at different angles. Even with mammograms from previous years to help them spot changes in the new images they miss  to  percent of malignancies.  The sensitivity of mammography is not what we want said tomosynthesis researcher Emily Conant chief of breast imaging at the Hospital of the University of Pennsylvania. We just cant see the darn cancer. To compensate radiologists err on the side of caution. For every  women screened studies show about  will be called back for more Xrays  and even an ultrasound MRI and biopsy. Only one of those  will turn out to have cancer. The major criticism of mammography has been the false positive recall rate. And women get freaked out about that said California radiologist Yuri Parisky vice president of the National Consortium of Breast Centers. Tomosynthesis uses computer wizardry to tackle these obstacles although it doesnt reduce the ouch factor because the breast still has to be compressed. First an Xray tube sweeps over the breast acquiring  lowdose images at multiple angles. Then the digital data are reconstructed into thin highresolution breast slices imagine a stack of orange slices that the radiologist can scroll through in order or view individually. All in a matter of seconds. It should help us overcome the camouflaging problem said Mark A. Helvie a University of Michigan radiologist who has worked on GEs tomosynthesis system.  So how much will it help The answer is complicated which is why Hologic proposed and the FDA approved using D in combination with D rather than as a replacement. The combo taken simultaneously will double a womans radiation exposure but the total dose will still be beneath the limit set long ago by the FDA. With D images cancerous lesions generally have welldefined borders. Radiologists are used to dismissing such welldefined spots as benign because thats usually the case with D images. Radiologists were taught to be aware of this potential pitfall before participating in Hologics first study done under experimental conditions so patients were not affected. Nonetheless the doctors identified fewer cancers with D plus D than D alone their accuracy dropped from  percent to  percent. For a second study training was beefed up and radiologists detection rate with D plus D was a bit better than with D alone  just as in most university studies. Radiologists training is critical to optimal performance Hologic told the FDA which is requiring both radiologists and technicians to take an intensive course. Another concern D has not been as good as D at imaging microcalcifications. These flecks of calcium often signal an early malignancy that is still confined to the milk ducts called DCIS ductal carcinoma in situ. Researchers such as Penn medical physicist Andrew Maidment are tweaking the technology to make microcalcifications more visible. But some experts believe detecting fewer milk ductconfined cancers  which now account for almost a quarter of all new cancer diagnoses  might not be a bad thing because some will never go on to invade surrounding breast tissue. Since doctors cant predict these preinvasive cancers are now treated  critics would say overtreated  with surgery radiation and often hormone therapy. By the same token doctors cant guarantee that catching and treating an aggressive cancer early will keep it from returning and growing deadly. Until we can tie the molecular biology of cancer into early detection were not going to be able to distinguish the good the bad and the ugly no matter how sophisticated the imaging system said Penns Conant. The one quandary that tomosynthesis is almost sure to relieve is the falsealarm rate. With more and better images radiologists can assess ambiguous lesions without automatically calling women back for more Xrays. Studies by Hologic and others suggest D plus D could cut the falsepositive recall rate by more than a third  so five or six women would be unnecessarily freaked out instead of nine. To a radiologist it may be a negative because youre potentially decreasing revenue said Parisky the California radiologist. But its good for the health system and good for patients. Hologics system is already in use in Europe Brazil and Canada. The company says several hundred U.S. breastimaging centers have a Hologic D system than can be upgraded to D with software that costs . Over five years this upgrade would cost about  more per patient the company says. Hologic is also seeking insurance coverage for D. The impact of tomosynthesis like that of digital mammography may take a decade to shake out. Even then D may not settle the debate over how many lives early detection saves and whether this benefit outweighs the risks and costs of false alarms. Almost every month another analysis is published while screening guidelines vary with most  but not all  calling for annual mammograms starting at age . Tomosynthesis could tip the scales. This is the biggest improvement in the history of mammography said Maidment the Penn physicist."