The Role of Diagnostic Ultrasound - Zero Gravity - HD

Use of Ultrasound in the Space Program

The subject of my talk is the use of ultrasound in the space program and what we are doing at the Johnson Space Center with diagnostic ultrasound.

Hazards of the Space Environment

Space is a hostile environment. Among the occupational hazards that our astronauts are subjected to is radiation exposure. They get acute radiation syndromes due to solar particle events, and the radiation causes cardiovascular disease and degenerative effects. And carcinogenesis. Zero gravity has numerous pernicious effects. You get vestibular and sensory motor alterations, orthostatic intolerance during re-exposure to gravity, reduced aerobic capacity, muscle mass strength and endurance, and your bones thin out. You get osteoporosis and fractures, intervertebral disc damage after re-exposure to gravity.

They also get renal stones because of the negative calcium balance from the bone loss.

Focus on Space Flight Associated Neuro-ocular Syndrome (SANS)

But what I want to focus on is what is turning out to be a serious impediment to deep space exploration. But what I want to focus on is this entity that was just recently described, space flight associated neuro ocular syndrome, or SANS, which is going to turn out to be a major impediment to long term deep space exploration.

History of Human Space Habitation

Mankind has been living in space since the year 2000. That's when the International Space Station was completed. Over 60 expeditions have been completed. It's in lower earth orbit. Each mission duration is between six months and a year. It's run by a consortium made of the US, Russia, the EU, Canada, and Japan. And the crew consists about five or six people.

Ultrasound Facilities on the ISS

Ultrasound may not have a very big profile in many radiology departments compared to what it was a few years ago, but there is a radiology facility on the ISS and the only off earth imaging facility. There is an ultrasound unit, there's no CT or MR or x-rays. There is a GE Vivid Q, and that is it. And that is what the astronauts have to use to diagnose all these entities that I just described.

They use it for ocular ultrasound to diagnose renal stones because renal stones are a big problem for these astronauts and for bone densitometry.

What is SANS?

What is SANS? Visual disturbances have been described since the beginning of space flight, but since the term was just coined about 40 years ago, 37% of US orbital segment crew members developed visual impairment and one or more of these features of SANS, which are refractive errors and scotomas that get big blind spots. You get globe flattening, you get hyperopic shift or greater than 0.5 diopter. And on examination of the retina, they see they get cotton wool spots, choroidal folds, and optic disc edema.

This is just a chart of the USOS individuals with SANS findings. You can see a substantial number of people on long-term exposure to zero gravity develop these findings. These findings can last for years after they come back down to earth. And in some cases, the visual impairment is permanent, and the number of people rises from 37% to 60%. For those who have been on long duration missions, that's six months or longer.

So what's that gonna mean for the two year Mars mission that's planned for 2030?

Clinical Findings and Images

Here's some pictures of astronaut. This is before pre-flight, and at the bottom is post-flight ophthalmoscope. You can see these fold in the choroid. They look like fold in a rug or carpet. And this white thing here is a cotton wool spot. This is a pre-flight image of the optic disc. This is normal and this is post-flight pap edema.

The Russians experience the Russians have a lot of experience with the long duration space flight, the Salut and the Mir space stations, which are operational until 2001. And they found that eight out of 16 cosmonauts had optic nerve edema on landing. They did transcranial doppler and there was increased velocity in the straight sinus. However, interestingly, no cosmonauts have reported symptoms of SANS, and that's a discrepancy that's not being explained. But they did use lower body negative pressure devices.

Etiology of SANS

So as far as SANS is concerned, the underlying etiology is unclear. It was initially thought to be increased intracranial pressure, but they did lumbar punctures on people in low gravity. And they found that the tran pressure was normal. So now they think it's localized orbital CSF pressure elevation without entries in cranial pressure, in elevated intraocular pressure is thought to be a mediating component.

This chart here shows the ocular pressure obtained before flight and after flight in gray and during flight on the space station. You can see that the intraocular pressure rises and then falls when the patient returns to earth. So elevated pressure within the eyeball is a feature.

So there are a couple of theories. One is cephalad fluid shifts. So fluid on earth. Your body fluids tend to pool in your lower extremities without gravity sort of distributed more equitably. And this shift of fluid from your legs to your head is thought to be one factor. The other thing is venous congestion, because unlike in the lower extremities, there's no muscle pump or valves in the veins of the eye and brain. So loss of the gravitational vector impair cerebral venous and lymphatic drainage from the skull. And that may be a factor in SANS.

And incidentally, just a couple of in the past two weeks, we've had two astronauts have developed upper extremity DVTs. That's extremely rare to get upper extrem subclavian and jugular vein thrombosis in the absence of a coagulopathy or a central line. But we just had two astronauts who did the same.

Example of Cephalad Fluid Shift

This is an example of what cephalad shift looks like. These are a group of astronauts. These are two Russians and a German. And this is what happens when you put fluid in a balloon on Earth, it tends to sag because gravity pulls it down. This is what happens in zero gravity and can look at the faces of the astronauts. Just one day after they went up into space, their faces have become puffy due to the cephalad shift.

Ultrasound Protocol for Monitoring SANS

So how does ultrasound fit in? This is our imaging protocol. They get an orbital ultrasound pre-flight in flight, and then every 30 days and until they return. This is remotely guided by a radiologist at mission control. So we had Anderson go to mission control and we talk to them by a real time video link like this astronaut here, and we get an image of the orbit. And then we repeat that at Anderson within three days of landing. They get a 3T MRI of the brain and orbits pre-flight, and within three days of landing.

So this is what we look for. This is a normal orbit. This is an anterior chamber, the posterior chamber, the lens, this is the optic nerve here. And the optic nerve sheath is that slightly hypoechoic area on each side of the nerve. We look at the shape of the globe. It should normally be round. We measure the diameter of the optic nerve and the optic nerve sheath diameter.

So this is a normal eyeball. And we also obtain dopplers from the central retinal artery.

This is a patient with SANS. Note that you have flattening of the globe, so it looks more ovoid and egg shape. The optic nerve becomes kinked. This is the equivalent MRI obtained after landing note, the optic nerve is kinked and that the kinking is this area here. You can see how it bends. And the optic nerve sheath diameter, which is the optic nerve sheath is demarcated by this green line here and this purple line here, and is shown on this T2 image as this high signal area here outlining the optic nerve in the middle. So this area is widened and they also get increase renal artery peak systolic velocity.

These are just some results. I can see the n is very small because we only have about 30 or 40 astronauts that have been studied. But if you look at the optic nerve sheath diameter, it increases in patients with globe flattening and the patients with kinking.

So this is where we are. We have an ultrasound unit there. What's the next stage?

Proposals to Advance Ultrasound on the ISS

So we have a couple of proposals before NASA to advance radiology on the ISS. The thing is, they're not using the elastography or contrast. So one project, which we advance is to use strain elastography because if there is increased intraocular pressure, perhaps we can use orbital stiffness as a metric of intraocular pressure and maybe optic nerve stiffness. So this is a pilot project where we did a strain elastogram. This is the equivalent gray scale image of the orbit. And you can see here that the aqueous, the anterior and the posterior part of the vitreous here show different degrees of compression stiffness.

Since you only have an ultrasound unit here, perhaps contrast can be helpful for evaluating flow, particularly blood return. The thing is, we don't have any data on what microbubbles will do in zero gravity. So we have put forward ideas for performing in vitro studies on phantoms to evaluate the properties of microbubbles and their interaction in zero gravity. What is the resonant frequency? What is the rupture frequency? And how do they flow in zero gravity? 'Cause there's currently no information about that.

And then the next thing that we may need on the space station is a transvaginal probe to evaluate the IUD and endometrium. The reason for that is personal hygiene while menstruating in zero G is challenging. So the waste disposal systems about the ISS that reclaim water from urine are not designed to handle menstrual blood. So many astronauts up for menstrual suppression either using depo-medroxyprogesterone or a levonorgestrel IUD or DMPA or depo methyl progesterone. But the thing about these hormonal agents is that they increase bone loss, which potentiates the bone loss that they get from zero gravity. So this is actually turned out to be quite an issue.

So if someone comes up with a feminine hygiene product that works well in zero gravity, NASA would like to hear from them. But anyway, so these are the three things which we are trying to move forward for the ultrasound unit.

Future Plans for NASA and Deep Space Missions

So anyway, the future, this is just graph showing what NASA's plans are for the future. So we are currently at phase zero, which is to solve exploration and mission challenges to research and systems testings on the ISS. So the next stage is as the ISS grows, as the next module goes on, they're probably gonna expand the radiological facilities, maybe a small x-ray unit. And there are some designs on the drawing board for a CT, which you have one detector and one tube. And because of zero gravity, you can rotate the patient like a rotisserie chicken. But that is still that is currently the design. And we are probably gonna have to test that on the ISS.

SANS is emerging as a major problem for deep space missions. Obviously if you have a flight to Mars and the pilot at the far end can't see when you're about to land. But ultrasound is gonna be the main imaging modality for deep space missions. And so I think imaging on deep space missions, research testings and trained to operate independently is going to be the future. So there's one place where ultrasound is gonna be predominant. There's not gonna be a three Tesla on the Mars mission. That's going to be an ultrasound unit, possibly if there is an imaging facility at all.

Questions and Discussion

Questions.

I was just gonna ask about that. 'Cause in by if you're counteract microgravity, you just generate artificial gravity the way they did in 2001. Yes. And it should be possible to test that experimentally with an animal model by having it's hard to do on a human scale maybe, but for you could have one animal that's rotating in artificial one G and one not and just compare and see what happens.

You mean animal for what? Contrast or

No, to test one in a artificially generated gravity and the other in microgravity,

Right? You're talking here, but a centrifuge would be easier to test that with an animal model than human.

Oh, yes. This is actually a solution for SANS. This is the European Space Agency artificial gravity human centrifuge to mimic gravity. Yeah, but how much g do you need for how long? Nobody knows the answer. No, there's a lot that people don't know about SANS, And that's exactly what they did in 2001. So I got the Arthur C. Clarke for saw this coming.

Okay. I was gonna say the same thing. The solution to this is to spin the ship they're on. And in the movie Mars, they demonstrated it. You don't need to experiment it. This is physics. Every the citri force could be made to equal the force of gravity and the mass of the people on it doesn't matter. It's only related to the speed with which you spin it and the radius of the circle you spin it around. But I think that would solve these problems. But I wanted to thank you for opening our eyes to this problem.

Oh yeah. We I'm very glad that you're continuing this work. I was involved with the first ultrasound unit on ISS. And I also wrote a thesis on that stuff. But anyway, the question you have to NASA is they have to address important problems, just like you said. And looking at bone density with ultrasound is a possibility. Yeah, That, And have you had any experience with that, or,

No. We don't personally, I personally haven't, but they that's what they're doing here. But I think NASA is going to reach will need some expertise from the radiological community as they expand the radiological facilities and the ISS. So I am hopeful that maybe members of this society are gonna par someone wants to go up there and set up the first CT unit, and perhaps you get to go first.

Yeah. My vision's 20/20 I like to keep it that way.

Yeah.