Dr. B. Leonard Holman, Cooke Professor of Radiology at Harvard Medical School (HMS), a pioneer in nuclear medicine best known for his work on the effects of cocaine addiction, died of cancer Sunday at his home in Newton. He was 56.

A native of Sheboygan, Wisc., Holman was also the chair of radiology at Brigham and Women's Hospital in Boston, having worked there since 1970. He joined the HMS faculty in 1981.

Holman graduated from the University of Wisconsin in 1963, receiving his medical degree from the University of Washington three years later.

At Brigham and Women's, Holman was one of the first researchers in the field of nuclear medicine, leading the development of singlephoton emission computer tomography (SPECT).

This technique uses slightly radioactive dyes, which are injected into the bloodstream and then tracked in the blood by special rotating cameras. A three-dimensional image of blood flow is created, which doctors use to diagnose diseases of the brain, heart and other vital organs.

"Leonard Holman grew up with the field of nuclear medicine and isotopes and was the person that brought SPECT to its current state," said Dr. Harry Mellins, a long-time friend and colleague, as well as professor emeritus of radiology at HMS.

Holman gained renown in radiology circles in 1986 for his application of SPECT to identify brain activity associated with Alzheimer's disease.

While his work focused primarily on SPECT, some of Dr. Holman's most ground-breaking research came in 1987 when he used X-ray and CAT-scan imaging to analyze the bodies of several Egyptian mummies.

This research was part of a joint project between Brigham and Women's and the city's Museum of Fine Art to investigate the anatomy of 3,000-year old mummies without damaging them.

Holman was perhaps best known, however, for his study of cocaine's effects on the brain. Using three-dimensional scans of brain activity, he and his colleagues at Brigham and Women's discovered that cocaine impedes blood flow to the brain and other parts of the body.

They documented their findings in the educational film, "Cocaine and the Brain," produced by Holman, which is currently used by the government in the treatment of recovering cocaine addicts.

This study secured for Holman the prestigious Gold Medal of the Association of University Radiologists in 1996. The same year, Pannona University in Hungary awarded him an honorary doctorate for his contributions to the field of radiology.

Even in his final years, Holman's advancing illness did not prevent him from leading an active life. His friends describe him as an accomplished digital photographer as well as an avid skier and golfer.

Colleagues at HMS and Brigham and Women's remembered Holman as a highly regarded scientist who endeared himself to his peers at both institutions. Mellins said his friend was "a person of great character [and] a man of enormous integrity."

HMS Dean of Faculty Affairs Eleanor Shore said that she "enjoyed Dr. Holman and had the highest respect for him."

Dr. Holman is survived by his wife, Dale; two daughters, Amy and Allison; and his mother, Sophie.