This article is part of Overlooked, a series of obituaries about remarkable people whose deaths, beginning in 1851, went unreported in The Times.

Margaret Chung knew from age 10 that she wanted to become a medical missionary to China. She was inspired by stories her mother had told of life in a mission home, where her mother stayed as a child after emigrating from China to California. It is believed that she named Margaret after the home’s superintendent.

Religion was an important part of young Margaret’s life in California. She was raised in a Presbyterian household in Santa Barbara, where her father insisted that the family pray before every meal and sang hymns with the children before bed.

So it was a blow that after graduating from medical school, at the University of Southern California, in 1916, her application to be a medical missionary was rejected three times by administrative boards. Though she had been born on United States soil, she was regarded as Chinese, and no funding for Chinese missionaries existed.

Still, following that dream led her to a different accolade: Chung became the first known American woman of Chinese ancestry to earn a medical degree, according to her biographer.

She opened a private practice in San Francisco’s Chinatown. It was one of the few places that would provide Western medical care to Chinese and Chinese American patients, who were often scapegoated as the source of epidemics and turned away by hospitals. (Her father died after he was denied treatment for injuries he sustained in a car accident.)

As a physician and surgeon during the Second Sino-Japanese War (beginning in 1937) and World War II, she was praised for her patriotic efforts, including starting a social network in California for pilots, military officials, celebrities and politicians that she leveraged to help in recruitment for the war and to lobby for the creation of a women’s naval reserve.

Every Sunday she hosted dinners for men in the military, catering for crowds of up to 300 people, who called her “Mom.” Her efforts caught the attention of the press, which portrayed her as representing unity between China and the U.S., allies in the war.

Margaret Jessie Chung was born on Oct. 2, 1889, in Santa Barbara, Calif. At the time, the 1882 Chinese Exclusion Act was in full force. Her parents, who had immigrated from China in the 1870s, were barred from obtaining U.S. citizenship under the act. They faced limited job opportunities, so the family moved around California as they looked for work. Her father, Chung Wong, was a former merchant who toiled on California farms and sold vegetables. Her mother, Ah Yane, also farmed and sometimes worked as a court interpreter.

Margaret herself was no stranger to hard labor. She took on farming chores when her parents were unwell and helped raise all 10 of her siblings, duties that disrupted her schooling; she did not complete the eighth grade until she was 17. To fund the rest of her education, she spent summer evenings knocking on doors to sell copies of The Los Angeles Times as part of a competition for a scholarship, which she won. It paid for preparatory school, which enabled her to gain acceptance to the University of Southern California College of Physicians and Surgeons in 1911.

“As the only Chinese girl in the U.S.C. medical school, I am compelled to be different from others,” she said in a 1913 interview. She reinvented herself as “Mike,” slicking back her black hair and dressing in a long blazer draped over a shirt and tie, completing the outfit with a floor-length skirt. She worked throughout college, according to her biography, sometimes scrubbing dishes at a restaurant while studying textbooks propped on a shelf.

After she graduated and was rejected as a medical missionary, Chung turned to surgery, performing trauma operations at Santa Fe Railroad Hospital in Los Angeles. Touring musicians and actors used the hospital; most famously, she removed the actress Mary Pickford’s tonsils.

Chung soon established her own private practice in Los Angeles, with a clientele that included actors in the movie industry’s early days in Holllywood.

While accompanying two patients to San Francisco, Chung fell in love with the city’s landscape, its dramatic hills cloaked in fog. After learning that no doctor practiced Western medicine in the city’s Chinatown, home to the largest Chinese American population in the country, she left her Los Angeles practice and set up a clinic on Sacramento Street in 1922.

San Francisco was isolating. People from the community invited Chung out, but she declined, writing in her unpublished autobiography, “I was embarrassed because I couldn’t understand their flowery Chinese.” Rumors persisted that because she was single, she must have been interested in women. She was protective of her personal life, but her biographer, Judy Tzu-Chun Wu, said Chung had frequented a North Beach speakeasy with Elsa Gidlow, who openly wrote lesbian poetry.

Chung’s practice initially had difficulty attracting patients. But as word spread, her waiting room filled, in some cases with white tourists curious to see her Chinese-inspired furniture and her consultation room, whose walls were plastered with pictures of her celebrity patients.

Years of planning and community fund-raising culminated in the opening of San Francisco’s Chinese Hospital in 1925. Chung became one of four department heads, leading the gynecology, obstetrics and pediatrics unit while still running her private practice.

When Japan invaded the Chinese province of Manchuria in September 1931, an ensign in the United States Naval Reserves, looking to support the Chinese military, visited Chung at her practice. She invited the man, who was a pilot, and six of his friends for a home-cooked dinner. It was the first of many that she would host almost every night for months. It was, she wrote in her autobiography, “the most selfish thing I’ve ever done because it was more fun than I had ever known in all my life.”

Every Sunday, “Mom” personally catered suppers for hundreds of her “boys.” By the end of World War II, her “family” swelled to about 1,500. To help keep track, everyone had a number and group: Leading pilots were the Phi Beta Kappa of Aviation; those who could not fly (including celebrities and politicians) were Kiwis; and the submarine units were Golden Dolphins.

She called upon influential members of her network to secretly recruit pilots for the American Flying Tigers, an American volunteer group that pushed back against Japan’s invasion of China. She also enlisted two of her Kiwis to introduce a bill in the U.S. House and Senate that led to the creation of Women Accepted for Volunteer Emergency Services in 1942, a naval group better known as the WAVES. Eager to support her country, she sought to join the group but her application was rejected.

Despite her efforts, no official recognition of her contributions ever came. After the war ended, attendance at her Sunday dinners dwindled. Nevertheless, Chung continued to practice medicine, visit her military “sons” and write her memoir.

She died of ovarian cancer on Jan. 5, 1959. She was 69.

Dr. Leslie Hendeles began prodding the Food and Drug Administration to reject a decongestant in cold medicines when he had a mop of curly red hair and Bill Clinton had just become president.

By the time opposition to the drug had coalesced, Dr. Hendeles was appearing, at age 80, as an expert to testify before the agency’s advisers, his hair white and his overview of the ingredient spanning 50 years.

His advocacy culminated in the advisory panel’s unanimous vote on Tuesday, when it concluded that the decongestant, a common ingredient in cold and flu remedies, is ineffective.

Prompted by the news, consumers threw open their medicine cabinets upon learning that the decongestant, phenylephrine, was listed in more than 250 of their go-to drugs for congestion like some versions of DayQuil, Sudafed, Tylenol and Theraflu. And the decision has caused some confusion — experts say the ingredient still works in nasal sprays, just not when taken orally in pill or liquid form.

Given that the drug is considered safe, experts say there is no need to throw away the products, which contain other ingredients that do work.

Nothing will change immediately. F.D.A. officials have to review the panel’s decision, solicit public comments and most likely will give drug makers some time to adjust or swap out ingredients rather than face a decision to strip store shelves of so many consumer staples. Other delays could occur if the companies contest the actions in court. And some experts, notably Dr. Scott Gottlieb, a former F.D.A. commissioner, have long maintained that phenylephrine does work, to some extent. Some defenders of the drug may try to oppose any action that banishes the decongestant altogether.

But how phenylephrine stayed on the market this long despite decades of studies and questions is a tangled story involving old drug standards dating back to a law signed by President Kennedy, the proliferation of meth labs using everyday cold remedies in the 1990s, and even the pandemic.

Like other federal agencies, the F.D.A. can move glacially, at times hampered by antiquated rules and a morass of regulatory procedures.

“There is no question that regulation of over-the-counter medications was broken for many years,” said Dr. Joshua Sharfstein, a former agency official and vice dean at the Bloomberg School of Public Health at Johns Hopkins. The latest moves, he said, indicate that the “agency is only now getting its handcuffs off.”

One could argue the process of dissecting phenylephrine — a drug used for dilating eyes and calming hemorrhoids — took roughly six decades. The Kennedy era had ushered in a new law that required the F.D.A. to evaluate a drug’s effectiveness in addition to existing safety standards.

It wasn’t until 1976 that the F.D.A. began reviews of over-the-counter cold medicines, like phenylephrine, as a class of drugs.

But by the early 1990s, the decongestant still hadn’t received a full approval, and the lengthy delays had attracted the attention of Dr. Hendeles and a group of pharmacy professors at the University of Florida.

They would become the one constant in the last 30 years of phenylephrine’s history by putting pressure on the F.D.A. to do something.

Dr. Hendeles published his first critique of the drug in 1993, noting that the agency had oversight of two more popular decongestants that were effective and a third that was not: phenylephrine. The medication was meant to constrict blood vessels and clear congestion in the nose. But it was destroyed in the stomach, he wrote in a medical journal. That meant most of the medication didn’t make it to the bloodstream — much less to the nose.

By the 2000s, what would seem like an unrelated problem was surging: Illegal methamphetamine labs in rural areas on the West Coast were exploding, as was abuse of the illicit drug.

Meth cooks’ ingredient of choice was one of the most common decongestants on the market at the time, pseudoephedrine, which could be found at any drugstore.

By then, it was one of two decongestants available for congestion relief; a third had been pulled in 2000 after studies tied it to strokes.

The meth crisis prompted the passage of state and federal laws to restrict sales of products containing pseudoephedrine, and consumers had to show identification and sign a ledger to buy it from behind the counter or a locked cabinet of a pharmacy.

Concerned about losing sales, companies with medicines containing the popular meth additive turned to the last option authorized by the F.D.A.: phenylephrine.

Dr. Hendeles said he was dismayed to see the ingredient in medicines lining pharmacy shelves, knowing patients were complaining that the replacement didn’t help them at all.

He teamed up with a colleague, Dr. Randall Hatton, and they dug deeper, plumbing the data used in the 1970s for the drug’s initial approval.

Dr. Hatton unearthed memos to the F.D.A. from the 1960s and 1970s that had not been peer-reviewed. He and colleagues ran the data in modern analysis software and concluded that the drug was no better than a placebo.

As their research progressed, Dr. Hendeles tried to reach the F.D.A., where he had once been a visiting scientist. He was not breaking through, he said. So he turned to the office of U.S. Representative Henry Waxman, a crusading California lawmaker, for help.

Mr. Waxman fired off four letters, citing the professors’ findings and imploring the agency to act. “F.D.A. has a duty to arm Americans with the information they need so that they don’t waste their hard-earned money on medicines that do not work,” he wrote in a letter in 2006.

The F.D.A. replied that same year, restating the findings of its 1976 decision. The letter suggested that if a consumer did not get relief from phenylephrine, “they have the option of not purchasing it.”

Dr. Hendeles, the letter said, was free to petition the agency.

And he did. Dr. Hendeles requested a dosing review and examination of use of the drug for children. That led to a public F.D.A. advisory hearing in 2007. There, the Consumer Healthcare Products Association, the business trade group that represents the makers of over-the-counter medicine, maintained that the drug worked.

Dr. Hendeles recalled what he considered show-stopper testimony. Representatives for Schering Plough, at the time the maker of Claritin-D, which contained the restricted decongestant pseuodoephedrine, told advisers that they had studied its rival, phenylephrine, and found it had no effect. The company’s newspaper ads touted its “bold move” to keep the “powerful formula” for Claritin-D, a letter by Mr. Waxman noted.

Still, the advisory committee voted 11 to 1 that “evidence is supportive” that phenylephrine “may be effective,” and called for more research.

Eight years passed.

Then Dr. Hendeles and colleagues pounced on a study that emerged from Merck, which had acquired Schering Plough. The company examined the drug at the authorized dose and at a dose four times as high, and again found it did not relieve symptoms. Merck also funded a study on a slow-release formula.

But that stubborn head complaint — congestion — did not budge.

(In 2014, Merck sold Claritin-D, which still contains pseudoephedrine, to Bayer.)

The Florida pharmacists petitioned the agency for a ban, using the latest study as ammunition. But their efforts were stymied by what many former agency officials described as a beleaguered over-the-counter division, which had 31 staff members in 2018.

The staff had to follow “an arcane process that handcuffed the agency and provided insufficient resources to clear a backlog,” said Dr. Peter Lurie, who was an associate commissioner at the agency through 2017.

The Florida team ran into other hurdles throughout the years.

After this week’s vote, in posts on X, formerly known as Twitter, Dr. Gottlieb, who was the agency’s commissioner from 2017 to early 2019, called the panel’s decision “a shame.” He recalled that phenylephrine “was believed to be weakly active when we looked at this question around 2005/06. Now there may be no good, cheap, accessible options for consumers to get incremental relief.”

In an interview on Friday, Dr. Gottlieb said he thought more study of the ingredient was needed. “I think it’s premature to say that it doesn’t work,” he said.

Interest in the decongestant was renewed after pandemic legislation expanded agency staffing and overhauled the F.D.A.’s procedures for over-the-counter drugs so that decisions would be more aligned with those in its prescription drug division.

Soon after, the F.D.A. team took up the longstanding issues with the decongestant, producing a painstaking, 89-page review of phenylephrine that the advisory panel combed as the basis for its decision. (The agency’s report confirmed the findings of Dr. Hendeles and his colleagues, and also noted apparent bias in some of the 1970s data that led to the drug’s initial acceptance.)

“It was a joy to read,” Dr. Hendeles said.

When he testified before the panel earlier this week, Dr. Hendeles talked about a study from 1971 involving modified scuba masks to measure nasal congestion — the first finding phenylephrine to be a dud.

Other organizations including Public Citizen, the American College of Clinical Pharmacy and the National Center for Health Research also urged the panel to dispense with the ingredient. The industry association argued that the ingredient was effective and that low levels in the blood did not negate its effect. A statement from Kenvue, a spinoff of Johnson & Johnson, said products with phenylephrine are a small part of its business and it sells cold products without it.

When agency advisers cast their 16-to-0 vote, Dr. Hendeles was thrilled. “Nothing was as exciting and exhilarating as the vote,” he said.

Lawyers representing people who purchased cold and flu medicines containing phenylephrine are already announcing lawsuits against the drug makers, claiming the companies knew the decongestant was useless.

For now, the products remain on the shelves. “We feel vindicated for something that we worked on for a long time,” Dr. Hatton said. “But it’s not over.”

Judy Govatos has heard that magical phrase “you’re in remission” twice, in 2015 and again in 2019. She had beaten back Stage 4 lymphoma with such aggressive chemotherapy and other treatments that at one point she grew too weak to stand, and relied on a wheelchair. She endured several hospitalizations, suffered infections and lost nearly 20 pounds. But she prevailed.

Ms. Govatos, 79, a retired executive at nonprofit organizations who lives in Wilmington, Del., has been grateful for the extra years. “I feel incredibly fortunate,” she said. She has been able to take and teach lifelong learning courses, to work in her garden, to visit London and Cape Cod with friends. She spends time with her two grandchildren, “an elixir.”

But she knows that the cancer may well return, and she doesn’t want to endure the pain and disability of further attempts to vanquish it.

“I’m not looking to be treated to death. I want quality of life,” she told her oncologist. “If that means less time alive, that’s OK.” When her months dwindle, she wants medical aid in dying. After a series of requests and consultations, a doctor would prescribe a lethal dose of a medication that she would take on her own.

Aid in dying remains illegal in Delaware, despite repeated legislative attempts to pass a bill permitting it. Since 2019, however, it has been legal in neighboring New Jersey, a half-hour drive from Ms. Govatos’s home.

But New Jersey restricts aid in dying to terminally ill residents of its own state. Ms. Govatos was more than willing, therefore, to become one of four plaintiffs — two patients, two doctors — taking New Jersey officials to federal court.

The lawsuit, filed last month, argues that New Jersey’s residency requirement violates the Constitution’s privileges and immunities clause and its equal protection clause.

“The statute prohibits New Jersey physicians from providing equal care to their non-New Jersey resident patients,” said David Bassett, a lawyer with the New York firm Wilmer Cutler Pickering Hale and Dorr, which brought the suit with the advocacy group Compassion & Choices.

“There’s no justification that anyone has articulated” for such discrimination, he added. The suit also contends that forbidding New Jersey doctors to offer aid-in-dying care to out-of-state patients restricts interstate commerce, the province of Congress.

The New Jersey Attorney General’s office declined to comment.

“I’d like not to die in horrible pain and horrible fear, and I’ve experienced both,” Ms. Govatos said. Even if she enrolls in hospice, many of the pain medications used cause her to pass out, hallucinate and vomit.

To be able to legally end her life when she decides to “is a question of mercy and kindness,” she said.

It’s the third time that Compassion & Choices has pursued this route in its efforts to broaden access to aid in dying. It filed similar suits in Oregon in 2021 and in Vermont last year. Both states agreed to settle, and their legislatures passed revised statutes repealing residency requirements, Oregon in July and Vermont in May.

The plaintiffs hope New Jersey, another blue state, will follow suit. “We hope we never have to go before a judge. Our preference is to negotiate an equitable resolution,” Mr. Bassett said. “That’s what’s important for our patient plaintiffs. They don’t have time for full-fledged litigation.”

“It’s not the traditional process of trying to convince a state legislature that this is a good idea,” said Thaddeus Pope, a law professor at Mitchell-Hamline School of Law in St. Paul, Minn., who tracks end-of-life laws and court cases.

Dropping residency requirements in New Jersey could have a far greater impact than it will in Oregon or Vermont. The sheer population density along New Jersey’s borders — there are almost 20 million residents in the New York metropolitan area alone — means medical aid in dying would suddenly become available to vastly more people, and much more quickly than it would through legislation.

With a major airport and direct flights, “it’s easier to get to Newark than Burlington, Vermont,” Mr. Pope pointed out.

Many states where aid in dying is legal have relaxed their statutes because of findings like those in a 2017 study, in which about a third of California patients who asked a doctor about aid in dying either died before they could complete the process or became too ill to continue it.

But New Jersey still uses the stricter series of steps that Oregon first codified in 1994. That means two verbal requests to a doctor at least 15 days apart, a written request with two witnesses, and a consultation with a second physician; both must confirm that the patient is eligible. There’s a 48-hour wait after the written request before a prescription can be written.

Even without having to establish residency, “it won’t be a walk in the park,” Mr. Pope said. “You can’t just pop over to New Jersey, pick up the drugs and go back.”

Finding a doctor willing to prescribe can take time, as does using one of the state’s few compounding pharmacies, which combine the necessary drugs and fill the prescription.

Although no official would check to see whether patients travel home with the medication, both Mr. Bassett and Mr. Pope advise that the lethal dose ought to be taken in New Jersey, to avoid the possibility of family members facing prosecution in their home states for assisting in a suicide.

Still, preventing dying patients from having to sign leases and obtain government IDs in order to become residents will streamline the process. “Not everyone has the will, the financial means, the physical means” to establish residency, said Dr. Paul Bryman, one of the doctor plaintiffs and hospice medical director in southern New Jersey. “These are often very disabled people.”

Bills recently introduced in Minnesota and New York don’t include residency requirements at all, Mr. Pope noted, since they seem likely to be challenged in court.

“I think the writing’s on the wall,” he said. “I think all the residency requirements will go, in all the states” where aid in dying is legal. There are 10, plus the District of Columbia (though the legality in Montana depends on a court decision, not legislation).

Despite the often heated wrangling over aid-in-dying laws, very few patients actually turn to lethal drugs in the end, state records show. Last year, Oregon reported that 431 people received prescriptions and 278 died by using them, just .6 percent of the state’s deaths in 2022.

In New Jersey, only 91 patients used aid in dying last year. Roughly a third of those who receive prescriptions never use them, perhaps sufficiently reassured by the prospect of a swift exit.

Fears of “death tourism,” with an onrush of out-of state patients, have not materialized, said John Burzichelli, a former state assemblyman who helped steer New Jersey’s statute through the legislature and now favors allowing eligible nonresidents to participate.

“I don’t see lines of people at the tollbooths coming to take advantage of this law,” he said.

If her cancer returns and New Jersey has balked at allowing out-of-staters to legally end their lives there, Ms. Govatos contemplates traveling to Vermont. She envisions a goodbye party for a few friends and family members, with poetry reading, music and “very good wine and lovely food.”

But driving over the Delaware Memorial Bridge would be so much simpler. “It would be an incredible gift if I could go to New Jersey,” she said.

Tucker Marr’s life changed forever last October.

He was on his way to a wedding reception when he fell down a steep flight of metal stairs, banging the right side of his head so hard he went into a coma.

He’d fractured his skull, and a large blood clot formed on the left side of his head. Surgeons had to remove a large chunk of his skull to relieve pressure on his brain and to remove the clot.

“Getting a piece of my skull taken out was crazy to me,” Mr. Marr said. “I almost felt like I’d lost a piece of me.”

But what seemed even crazier to him was the way that piece was restored.

Mr. Marr, a 27-year-old analyst at Deloitte, became part of a new development in neurosurgery. Instead of remaining without a piece of skull or getting the old bone put back, a procedure that is expensive and has a high rate of infection, he got a prosthetic piece of skull made with a 3-D printer. But it is not the typical prosthesis used in such cases. His prosthesis, which is covered by his skin, is embedded with an acrylic window that would let doctors peer into his brain with ultrasound.

A few medical centers are offering such acrylic windows to patients who had to have a piece of skull removed to treat conditions like a brain injury, a tumor, a brain bleed or hydrocephalus.

“It’s very cool,” Dr. Michael Lev, director of emergency radiology at Massachusetts General Hospital, said. But, “it is still early days,” he added.

Advocates of the technique say that if a patient with such a window has a headache or a seizure or needs a scan to see if a tumor is growing, a doctor can slide an ultrasound probe on the patient’s head and look at the brain in the office. That way a patient can avoid costly, time-consuming and onerous CT scans or M.R.I.s. Instead of waiting for a radiologist to read the scan, a patient and a doctor can know right away what the patient’s brain looks like.

Dr. Mark Luciano, a professor of neurosurgery at Johns Hopkins, is using ultrasound to monitor hydrocephalus patients, who have shunts in their brains to drain excess cerebrospinal fluid. Patients need regular CT scans to see if the fluid is draining properly.

In an attempt to assess the windows, Dr. Luciano recently published a study of 37 patients who had the windows placed in their skulls, compared with a larger group of similar patients from the year before the method was developed.

Over a one-year period, he saw no risk of infection. The challenge now, he said, is to make the images from ultrasound scans better and to quantify what they show, he said, as well as to monitor their safety for several years.

But not everyone is won over.

Dr. Ian McCutcheon, a professor of neurosurgery at the University of Texas MD Anderson Cancer Center, said the window “is an intriguing idea.” But, he said, before he uses it to assess brain tumor patients he’d need evidence from a rigorous clinical trial that ultrasound is as accurate as an M.R.I. in detecting changes, like a growing tumor.

That trial, he said, “has not been done yet.”

Others, like Dr. Joseph Watson, director of the brain tumor program at Georgetown University, called the technique “frivolous.”

“You are going through a small port,” he said. “It doesn’t give you enough of a picture of the whole brain” that he gets with a CT scan or M.R.I.

But Mr. Marr’s doctor, Netanel Ben-Shalom, assistant professor of neurosurgery at Lenox Hill Hospital in New York, disagrees. In his experience, he said, “as long as the window is located above the tumor, the cavity is clearly demonstrated.”

Dr. Ben-Shalom was won over from the moment he tried implanting a window a few years ago. He was a resident at Johns Hopkins, and his patient had a brain tumor.

“It was amazing,” Dr. Ben-Shalom said. He could see the entire brain, he said, and all its structures.

He moved to Lenox Hill in January 2022, became a consultant for Longeviti, the company that makes the windows, and has been implanting and using its clear polymethylmethacrylate windows ever since.

On an afternoon earlier this year, Mr. Marr sat on a wooden chair in a tiny office at Lenox Hill, grinning as Dr. Ben-Shalom slid an ultrasound probe over the window in his skull. A cluster of medical students looked on.

For Mr. Marr, life was difficult after the removal of the piece of his skull to treat his swelling brain. His head was distorted, with a large dent. He was left with fatigue and dizziness because his brain was inadequately shielded from atmospheric pressure.

During the scan, Mr. Marr’s brain looked perfect, Dr. Ben-Shalom said. The midline that separates the two hemispheres — and which had been pushed to one side after Mr. Marr’s injury — was exactly where it should be. The structures of his brain looked normal, Dr. Ben-Shalom said. The ultrasound even showed his brain’s pulsing.

Mr. Marr is young and healthy but, Dr. Ben-Shalom said, anyone who has had brain surgery needs surveillance. If Mr. Marr comes in one day with nausea and vomiting or a severe headache, or if he had a seizure, his doctors would need to look at his brain. The acrylic window makes it easy, Dr. Ben-Shalom said.

At the University of Southern California, Dr. Charles Liu and his colleagues are taking the ultrasound idea a step further. In a research project, he is studying the use of ultrasound as a simpler and cheaper way to do the sort of studies now done with f.M.R.I., a method that uses M.R.I. scanners to examine the brain’s activity.

For the study, he needed a patient who required a skull restoration for medical reasons and who would volunteer to have one with a specially designed window. If the idea succeeded, he and the team thought they might some day be able to use the method on intact skulls.

The hope is to detect tiny signals from changes in blood flow in different parts of the brain as patients perform different activities. That, Dr. Liu said, “could give unprecedented insights into brain functions.”

He found such a patient — Jared Hager, 39, who had a traumatic brain injury when he crashed his skateboard. He had spent two and a half years with a large piece of his skull missing.

Dr. Liu met Mr. Hager when he was admitted to Rancho Los Amigos National Rehabilitation Center in Downey, Calif., part of the Los Angeles County public safety net health system.

When Dr. Liu met Mr. Hager, he was uninsured and homeless — he and his brother were living in a van. And Mr. Hager was missing a large chunk of skull. He was scheduled to have his skull restored, but Dr. Liu offered him a choice: a standard prosthesis or one with a specially designed window optimized for brain studies.

Before his surgery, the Rancho Los Amigos Foundation provided free housing at a facility next to the hospital for patients and their families. But Dr. Liu worried about what would happen after Mr. Hager was discharged.

“When you do this kind of surgery, it’s a big operation,” he said. “My goodness, what if we do surgery on this guy and he ends up in a van in downtown L.A.?”

Through the Rancho Los Amigos Foundation Dr. Liu got Mr. Hager an apartment in Long Beach.

Mr. Hager has become a regular presence in Dr. Liu’s lab, working with its scientists to discover as much about his brain as they can.

“I’m never going to stop helping with anything Dr. Liu needs,” he said.