1991 MRI Experiment Challenges Medical Assumptions

Back in 1991, a woman and her partner participated in an unusual scientific study involving sex inside an MRI scanner. Fast forward over three decades, and the images obtained during this experiment continue to stimulate discussion in the medical community about human anatomy during intercourse.

This study is often hailed as one of the more unconventional medical imaging experiments to date.

Prof. Ida Sabelis and her partner, Joep, a Dutch couple, never expected to find themselves in such a situation. It turns out they were well-connected; a friend, Dutch scientist Menno Victor “Pek” van Andel, was curious about the anatomical details of sex—something that hadn’t really been examined. He invited the couple to participate, and, surprisingly, they agreed.

Once inside the MRI, they were told to hold a fixed position while the machine captured a series of scans, each lasting several seconds. It wasn’t the most comfortable setting, but it yielded unprecedented results. For the first time, the medical field could see in real time how sexual organs interacted during intercourse—a concept that hadn’t been documented before.

Following this initial foray, researchers moved on to a more structured study using MRI technology to analyze the anatomy of sexual activity. Volunteers over 18 participated in 13 scans, which involved eight couples and three women, capturing images during sexual arousal and actual intercourse—though always in the missionary position. Participants had the option to stop, but none chose to do so.

The results were published in the British Medical Journal in 1999, challenging many long-standing medical beliefs. A key finding debunked the idea that penile movement occurs in a straight line, an assumption that had persisted for centuries, including representations in classic anatomical illustrations, like those from Leonardo da Vinci.

Instead, the MRI revealed that the penis curves within the female body during erection, adapting naturally without causing discomfort—almost like a boomerang. Additionally, researchers discovered that about one-third of the penis comprises a “root” that remains inside the body, something previously unknown.

There were also eye-opening observations made about the female anatomy. For instance, during sexual arousal without penetration, the uterus was seen shifting upward, while the vaginal wall extended. Interestingly, there was no increase in uterine volume, which contradicted earlier anatomical texts and highlighted how much of what was known was based on assumption rather than direct observation.

Another finding showed that women’s bladders filled quickly during intercourse, and researchers are still contemplating why this happens. Van Andel suggested it could be an evolutionary mechanism promoting urination post-coital to fend off urinary tract infections, but he acknowledged that this is still largely theoretical.

Even though the groundbreaking article was published on Christmas Eve 1999—a time when many researchers were away—it quickly became one of the most cited in the journal’s history. By 2019, twenty years later, it was recognized as one of the most unusual and impactful studies ever published by BMJ.

Today, the article continues to attract thousands of readers monthly, remaining one of the journal’s most popular pieces.

Recently, it gained traction on social media, with TikTok users sharing their astonishment over the MRI images and questioning how two people could fit in such a small space, given the loud environment of an MRI. Comments like “How is there room?” and “Anyone who’s had an MRI knows how intense it is,” reflect this shared curiosity.

Responding to the buzz, Sabelis noted in a podcast that despite the MRI’s loud noise, they managed to get through the experience. She mentioned that they never anticipated the long-lasting repercussions of their participation. “This was one of the first MRI machines, so capturing the images took time,” she explained. “From the next room, they told us to hold the same position for perhaps a minute, which was kind of funny.”

Interestingly, the couple originally planned to capture images in the missionary position, but the machine’s dimensions made that impractical. They ended up fitting into the narrow scanner, adopting a spooning position instead. “It wasn’t romantic,” she recalled. “It was more an act of love and scientific duty. Thankfully, we didn’t feel claustrophobic.”

Sabelis was driven by a desire to enhance the medical understanding of female anatomy, a subject she felt had too long been shaped by male-oriented assumptions. Reflecting on the images they captured, she acknowledged a pivotal realization: “Oh, this is how we really fit together.”

Dr. Arnon Makori, head of imaging at Assuta Medical Centers, emphasized that the study was more than just a risqué anecdote. It was a landmark demonstration of how medical imaging can capture physiological processes in real time.

He remarked, “This was a rare case where technology penetrated an area almost impossible to document for centuries,” fundamentally altering perceptions of human anatomy and the functions occurring during intimacy.

Makori added that MRI technology only began clinical use in the mid-1980s, making the study revolutionary for its functional imaging capabilities. Today, MRI is employed for many applications, like examining the heart and fetal movements, but then it represented a major advance.

He commended both the researchers and the volunteers for their bravery. “They had to lie together in a narrow scanner and perform under lab conditions. That’s no small feat,” he said, acknowledging the difficult yet audacious nature of the study.

When asked whether such research would encounter ethical hurdles today, Makori pointed out that modern studies need ethics committee approval. “Researchers must demonstrate that the benefits outweigh any discomfort,” he explained. In this instance, given full consent, he saw no ethical issues. “It opened a window into a physiological process that had never been observed or documented medically.”

More than 30 years later, the impact of this experiment persists, continuing to inform medical textbooks while stirring curiosity about the intricate relationship between the body, sex, and science.