Computer systems designed to make mammograms more accurate turn out to make them less reliable, according to the largest study to evaluate the increasingly popular high-tech versions of the common test for breast cancer. The study of more than 429,000 mammograms found that \"computer-aided detection\" systems did not help radiologists find more tumors and significantly increased the number of false alarms. The computer-aided detection systems require a radiologist \"who knows what he or she is doing,\" said Dr. Brien Shah, a radiologist with Advanced Diagnostic Imaging, president of the Saginaw Valley chapter of the Michigan Radiological Society and a staff member at the Wayne State University Medical School. \"It\'s a useful tool, but it\'s not the end all,\" said Shah. \"(The machines) invite you to take a second look. They can be a little hypersensitive.\"