Shortly before jurors were ushered into a Tucson courtroom for a murder trial earlier this month, the judge was considering a last-minute question about bruising.

The issue was whether it would be unfair to the person on trial, a mother accused of killing her son, to have attorneys ask witnesses about the boy’s bruises. According to the child’s siblings, his mother would cover up marks on the boy’s skin with makeup.

As the four attorneys and Pima County Superior Court Judge James Marner talked that morning, some things came up: Bruising is sometimes just part of a kid being a kid, while other times it’s due to abuse.

Exactly when and how a bruise occurred, and whether a mark is even a bruise at all, are legal and medical questions that arise frequently, says a local doctor who specializes in child-abuse cases, Dr. Dale Woolridge.

The medical director of the Southern Arizona Children’s Advocacy Center, Woolridge often testifies at trials.

And he had these questions about bruising — like the ones that came up in the recent murder trial — in mind when he approached a colleague last summer.

Woolridge, a professor of emergency medicine, pediatrics, chemistry and biochemistry at the University of Arizona, suggested a senior project to Urs Utzinger, an associate professor in the UA’s Department of Biomedical Engineering:

Create a device that can be used to determine the age of a bruise.

The idea stems from bilirubin scanners, Woolridge said, which medical professionals have been using regularly for the last several years to test for jaundice in newborns.

Bilirubin is a yellow pigment formed from the breakdown of hemoglobin, and sometimes newborns have trouble excreting it, which makes their skin look yellow.

Checking on bilirubin levels in a mark on the skin can also distinguish a birthmark from a bruise, he said, because birthmarks will not contain bilirubin.

The new device developed at Woolridge’s suggestion will take that process further and, eventually, could show not only whether a mark is a bruise, but also when it occurred by measuring how it reflects light.

So far, an all-female team of engineering students — which includes five from the biomedical department and one majoring in mechanical engineering — have created a device that collects data on bruising and shows whether a bruise is old. They also had help from a Ph.D. student, Devesh Khosla, who is studying electrical engineering.

The next step will be conducting more research and testing so the science can get more and more precise.

Samantha Davidson, a 21-year-old biomedical engineering student, said the device works by analyzing how light reflects on a bruised area. 

Eventually, it could be used not only in child abuse cases but also in worker’s compensation cases, domestic violence situations or other circumstances in which a person can’t answer questions about who or what caused a bruise.

Be the first to know

* I understand and agree that registration on or use of this site constitutes agreement to its user agreement and privacy policy.

“In the long run, we want to be able to collect data and then have it spit back out the day and the time,” she said.

The device Davidson and her peers created will be on display, along with more than 115 other projects, at the UA’s Engineering Design Day Monday.

“We’re using a specialized camera and, through our software, enhancing the image information in order to better evaluate the color of the bruise,” said another student researcher, Ghazal Moghaddami. The other four students on the team are Alexa Shumaker, Alexandra Janowski, Claudia Segura and Nattakanan Rotwiang.

The final version of the device will measure just a few inches across and hold a spectrometer, two microprocessors, a display screen and a memory card to hold the data of multiple patients.

Social workers and doctors will be able to take measurements by gently applying the portable device to affected skin.

The idea is to use what’s on the memory card and put it in a computer to analyze the data, Davidson said.

Dr. Mary Ellen Rimsza, who oversees the state’s annual child fatality review, says knowing the age of a bruise would make investigating child abuse cases much more precise.

“It can help in determining if the history given by caretakers is truthful, if the bruises happened at different times,” she said, “and help determine who may have inflicted the injury based upon who was with the child during the time period when the bruises occurred.”

Contact reporter Patty Machelor at or 806-7754. On Twitter: @pattymachstar.


Patty covers issues pertaining to children and families as well as people living with disabilities. She previously reported on court cases, with an emphasis on juvenile court. She has worked for the Arizona Daily Star since 2001.