Water-Based Whole-Body Ultrasound Scanners: Caltech Research & Midjourney Medical
In the span of just two months, two separate breakthroughs have put water-based whole-body ultrasound scanning on the map — one from academic research, the other from a surprising commercial player.
In April 2026, Caltech researchers published a peer-reviewed paper in Nature Biomedical Engineering demonstrating a water-immersion ultrasound tomography system. Then on June 18, 2026, Midjourney — the AI image generation company — shocked the tech world by announcing Midjourney Medical, a new division building a commercial "Ultrasonic CT" scanner with plans for a network of spa-like scanning centers.
Both technologies use water to enable whole-body ultrasound imaging. But they're very different projects. Here's what each one is, how they compare, and what they mean for the future of diagnostic imaging.
Why Water?
Before diving into the two systems, it helps to understand why water is the common thread. The core challenge with ultrasound is that sound waves reflect off air. Even a thin layer of air between the transducer and the skin will block most of the ultrasound energy. That's why conventional ultrasound uses gel — it eliminates the air gap.
Water takes this concept to the largest possible scale. The acoustic impedance of water (~1.5 MRayl) is nearly identical to human soft tissue (~1.6 MRayl), meaning sound waves pass from water into the body with minimal reflection. This allows ultrasound to enter the body from every angle simultaneously, enabling whole cross-sectional imaging that no handheld probe could achieve.
Project #1: Caltech Research (Academic)
Published: April 24, 2026 in Nature Biomedical Engineering
Lead: Lihong Wang, Bren Professor of Medical Engineering, Caltech
The Caltech system uses a vertical water tank where the patient sits with their head above water. A ring containing 512 conventional ultrasound transducers moves up and down the tank, scanning different cross-sections of the body. Critically, it captures three physical parameters simultaneously:
| Parameter | What It Measures | Clinical Value |
|---|---|---|
| Echo (Reflection) | Standard ultrasound echoes at tissue boundaries | Anatomical structure, organ boundaries |
| Speed of Sound | How fast sound travels through different tissues | Tissue characterization (fat vs. muscle vs. tumor) |
| Attenuation | How much sound energy is absorbed or scattered | Detects stiffness changes from cancer or inflammation |
The system was tested on 5 healthy volunteers, scanning their abdomens for 10 seconds at a time. The images were directly comparable to clinical MRI scans of the same regions. Next steps include clinical trials for liposarcoma monitoring in collaboration with City of Hope Medical Center.
Project #2: Midjourney Medical Ultrasonic CT (Commercial)
Announced: June 18, 2026
Division: Midjourney Medical, led by CEO David Holz
Tech partner: Butterfly Network (ultrasound-on-chip)
The Midjourney scanner, called the Ultrasonic CT, takes a different approach. Instead of 512 traditional transducers, it uses 40 Butterfly Network ultrasound-on-chip modules, each containing thousands of microscopic transducer elements — totalling roughly half a million elements per system. Under a deal signed in November 2025, Midjourney pays Butterfly $15M upfront and $10M/year for five years, with potential total value up to $74M.
The scanning experience is designed around a spa-like experience — patients step onto a platform in a shallow pool of warm water and are slowly lowered through the transducer ring. The company describes each transducer element as "like a dolphin using echolocation" — half a million dolphins all pinging you at once.
Important Caveats
Midjourney's announcement generated massive headlines, but there are important details that are easy to miss:
- "60-second scan" is a target, not reality yet. The current prototype takes about 20 minutes because the data pipeline can't move fast enough.
- No AI inside the scanner. Despite Midjourney being an AI company, CEO David Holz confirmed the actual imaging uses no AI — it's pure physics and signal processing. AI is used only for post-processing image segmentation.
- The core technology is Butterfly Network's. Midjourney licensed the ultrasound-on-chip technology rather than inventing it.
- First spa opens late 2027. The first Midjourney Spa in San Francisco is targeted for end of 2027, with mass deployment (50,000 scanners, 1 billion scans/month) targeted for 2031.
- Only ~12 people scanned so far. The team is roughly 9 people, and the prototype has scanned about a dozen individuals.
Head-to-Head Comparison
| Metric | Caltech (Academic) | Midjourney Medical (Commercial) |
|---|---|---|
| Announced | April 24, 2026 | June 18, 2026 |
| Lead / Company | Prof. Lihong Wang, Caltech | David Holz, Midjourney |
| Transducer type | 512 conventional piezo transducers | 40 Butterfly ultrasound-on-chip modules (~500K elements) |
| Scan time | ~10 seconds (demonstrated) | 60 seconds target / ~20 min current prototype |
| Parameters | Echo + Speed of Sound + Attenuation | Phase coherence imaging (Butterfly's proprietary method) |
| Status | Research phase, clinical trials starting | Prototype phase, licensing deal signed |
| Deployment | City of Hope hospital trials (liposarcoma) | Midjourney Spa, San Francisco — late 2027 |
| Regulatory | Not yet submitted | Not yet submitted (Butterfly chips FDA-cleared individually) |
| Cost model | Research-funded | Per-scan spa model (targeting affordability) |
| People scanned | 5 volunteers | ~12 people |
Why This Matters for Rad Techs
Whether either of these systems becomes clinically mainstream, they represent a fundamental shift in how ultrasound is being thought about:
- Ultrasound is scaling up. From a handheld probe to a whole-body scanner. Same physics, much bigger ambition.
- Non-ionizing imaging is gaining traction. Both projects emphasize safety and the ability to scan frequently without dose concerns.
- Convergence with AI. Midjourney's post-processing segmentation shows how AI could make ultrasound images more accessible and interpretable.
- New business models. The "scan as a spa visit" model could change how patients access imaging — for better or worse.
- Regulatory challenges ahead. Neither system has FDA clearance. The path from prototype to clinical use is long and uncertain.
The Bottom Line
- Water is the key enabler — it provides uniform acoustic coupling around the entire body, enabling whole cross-sectional ultrasound imaging.
- Caltech's system is rigorous peer-reviewed research with multiparametric imaging (echo + speed of sound + attenuation), currently in the clinical trial pipeline for cancer monitoring.
- Midjourney's Ultrasonic CT is an ambitious commercial project using Butterfly Network's chip technology, wrapped in a spa experience model — but it's still early-stage with many targets yet to be met.
- Neither is FDA-cleared or clinically available. The earliest realistic deployment is late 2027 for Midjourney; Caltech's timeline depends on trial outcomes.
- Both represent a future where ultrasound is no longer limited to a handheld probe — potentially making safe, fast, whole-body imaging accessible at a fraction of the cost of CT or MRI.