CT Colonography -Train at Home

The day is young, but the leading contender for Spam-of-the-Day is already in my e-mail inbox: CT colonography training at home.

I guess I'll file this tidbit under activities for consenting adults.

Crikey, I'd rather have my spleen removed through my nose...

Osirix App Now Available for iPhone

OsiriX , the wonderful open-source Mac image viewer, just announced the availability of an iPhone version.

Like a lot of imaging software, OsiriX lets one look at X-rays, ultrasounds, CT and MR images. Besides merely viewing, it also lets one reconstruct 3D images and rotate them around.

Unlike most imaging software, OsiriX is written by radiologists who also happen to be clever programmers. Also unlike most imaging software, OsiriX doesn't require a second mortgage. The full Mac-based version is free, and the iPhone app is $20.

Why should a non-physician care about Osirix? Because this little app will let you carry around a library of your own personal medical images. Even in my prior life as an internist, I always urged patients to keep their own copy of their more important images. The OsiriX app finally makes this easy and portable.

In the radiology biz, we call prior imaging exams "old films", and they can be staggeringly useful to a patient and their physicians. One of my patients once avoided having a risky lung biopsy simply because he happened to have an old film at home as a curiosity. This old film showed us pretty convincingly that the potential lung cancer we saw on his new film was actually a benign granuloma, and was unchanged over the intervening decades.

How do you get copies of your own images? Ask your local radiology department to burn you a CD in DICOM format. Most departments will also include free image-viewing software on the disk. If you're a Mac owner, download a copy of OsiriX, which will read virtually all of these disks, even if written by PC's.

If you're a geeky radiologist, you're probably already playing with the new app. If you're a non-geek, ask your teenager or local radiologist to put it on your phone for you.

The Amulets of Seramon

The title of this post sounds like something straight out of Buffy the Vampire Slayer. However, as far as I can tell, no actual vampires are associated with these amulets -- just a 3000 year old royal scribe and middle-class Egyptian mummy by the name of Seramon. A very nice article on this mummy and its amulets was just published on the science section of Apple's website.

Unlike a Buffy episode, Seroman and his wrapping remain undefiled in the Museum of Fine Arts and Archaeology in Besançon, France. Unlike Sunnydale, California, Besançon remains unhaunted by vengeful mummies, and any dread curses triggered by disturbance of the body seem to be on permanent hold. These artifacts were visualized using a CT scanner at the local hospital. The CT data was then reconstructed into high resolution 3D images using imaging software running on various Apple Macintosh computers. The resulting images were apparently detailed enough to read the spell from the Book of the Dead inscribed in hieroglyphs on the undersurface of a 48 x 32 x 18mm stone scarab.

Mummy CT is not a new story. CT has been used since 1979 to image mummies all over the world. However, the quality of the CT images has continued to improve immensely over the years, and the 3D reconstruction algorithms available today provide extremely natural-looking images.

The imaging of this mummy is also noteworthy in that it is

the first time wax amulets have been discovered in situ with non-invasive techniques.

Stone, metal and bone stand out on CT images rather well from other body organs. However, the beeswax used for these amulets has a CT density very similar to that of the mummy's soft tissues.

Our department is periodically asked to image paleoradiology patients such as this, including non-human specimens from mastodons, deep sea angler fish, and ancient musical instruments. When these kinds of cases roll in through our doors, it's a great day to come to work.

Imaging Mount St. Helens

Since Mount St. Helens blew its top in 1980, the U.S. Forest Service and the U. S. Geological Survey have kept a pretty close eye on this particular piece of Washington State. As far as I know, they aren't using X-rays on the volcano, but the images they are producing are still quite wonderful.


The U. S. Forest Service mounted a real-time web cam in September, 2004, aimed right down the throat of the volcano. In June 2007, they added a High Definition webcam to the site, with significantly improved images.


In 1992, Johnathan Lees (now a professor of geolocial sciences at the University of North Carolina, Chapel Hill) obtained tomographic images of Mount St. Helens. Instead of X-rays, he used P-wave seismic tomography to produce 3D velocity maps of the magma system beneath the mountain. Another big imaging difference: pixel size. In medical imaging, an image pixel typically represents a piece of tissue less than a millimeter in width. Lees' pixels were much less wimpy -- the smallest of them represented a chunk of the Earth 0.5 kilometer in width! The image below shows a tomographic slice from a 27.5 x 21 x 20 km target volume. For scale, the above-the-ground profile of the volcano has been drawn in green at the top of the image.


Lees, J.M., The magma system of Mount St. Helens: Non-linear high resolution P-wave tomography, J. Volc. Geoth. Res., 53 (1-4), 103-116 1992.

Since the big boom in 1980, St. Helens has continued to erupt. In the past 3 years, the volcano has progressively added 100 million cubic meters to the lava dome in its crater. However, this latest eruption has been so gradual that normal movies of it would be like watching grass growing, only not as exciting. Instead, the USGS created a time-lapse movie of this eruption from data collected between October 2004 and July 2007. (via Ars Technica).


What's in store for Mount St. Helens next? Will someone figure out a way to use MR or PET on the mountain? Perhaps we can harness gravity waves or neutrinos to create tomograms of the whole darned planet. If so, I'd pay cash money to see that.

And Then the Dinner Conversation Turned to Skulls...

What kind of dinner was this -- a gathering of murder mystery writers? A meeting of anthropologists, paleontologists or forensic pathologists?  Ghouls?

Nope, this happened at a recent meetup of bloggers in my area. A plural of bloggers has no trouble talking forever about their blogs and recent posts. We did no less. However, toward the end of the meeting, we slid off-topic, and talked about other matters.

My table neighbor described a gift she had given to her husband: several skulls. Most husbands might not appreciate such a princely gift, but hers did. I just happen to be that kind of husband myself. I am not only fond of skulls, but also see a fair number of them at work.


The conversation then segued to good places to buy skulls. Sweeney Todd would have no problem finding one, but where does a non-demon-barber type shop for such a thing?

As it turns out, it's actually not hard to buy a whole head at a local slaughterhouse. However, if your main interest is the skull, you will first have to remove a fair amount of squishy soft tissue (this includes brains). If you are not daunted by the thought of this, Google can be your best friend. Thus begins a very brief tangent into what it takes to clean a skull.

My first search -- "stripping bones" led me to a cute but irrlevant YouTube video that is mildly not-safe-for-work. However, this search didn't immediately yield any practical tips that I'd want to try at home.

I had much better luck with "cleaning bones", which led to several possible approaches. However, I'm not too wild about soaking a large head in a hydrogen peroxide solution, or boiling it on my stove. I'm not squeamish, but one of the many good reasons I went into radiology in the first place was to avoid having to deal with messy body parts. For the same reason, I'd rather not raise a colony of dermestid beetles at home. A piranha tank is similarly out -- besides, owning a personal pirahna appears to be illegal in my state.

If one steps back from the abyss of DIY skull maceration, one is pretty much left with outsourcing the job. If one wants to send off a bag of money and get back a skull, there seem to be no end of sites offering this service.  To see for yourself, just Google the phrase "platypus skull".

At this point, our cranial conversation moved briefly to a diamond-encrusted skull that may still be on the market for a mere $100 million. Admittedly, this looks very cool, but I may just spend my first $100 million on something else.

In our final calvarial communications, I suggested to my fellow blogger one possibility for topping her previous gift -- a way in which she could essentially give her husband his own skull for Christmas.

All she has to do is to figure out some way of getting a CT scan of her husband's head when he isn't paying attention. The scan data can then be reconstructed as a 3D picture showing just the bones. Better yet, there are actually companies out there who will take this same CT data and print it in 3D using stereophotolithography -- producing a life-like plastic skull exactly the same shape and size as her husband's.


Hmmm, my wife always says that I'm hard to shop for at Christmas time. Maybe if I accidentally leave a copy of this post lying somewhere around the house...

Image Gently

If Google led you here thinking this was a post about a lost sequel to Douglas Adams' holistic detective, turn back! Instead, it concerns a widespread movement to reduce radiation dosage in children.

A recent article by Brenner and Hall raised important concerns about safety in patients undergoing computed tomography (CT).

Brenner, D.J., Hall, E.J. (2007). Computed Tomography -- An Increasing Source of Radiation Exposure. New England Journal of Medicine, 357(22), 2277-2284. DOI: 10.1056/NEJMra072149

This paper is aimed primarily at non-radiologists. The authors give a nice review of CT, the radiation dose from CT scans, the biological effects of low doses of ionizing radiation and the cancer risks associated with CT scans.

The authors raise particular concern for pediatric CT use, which has increased sharply since 1990. One factor leading to this increased CT usage in children is the growing adoption of rapid multi-detector CT machines. Prior to the current generation of scanners, most children's imaging was performed under sedation. These speedy new MDCT units can complete an entire study in as little as one second, obviating the need for sedation in the majority of cases.


Most of the concern about radiation dose centers around cancer risk. Estimating this risk is not straightforward. As the authors point out:

No large-scale epidemiologic studies of the cancer risks associated with CT scans have been reported.

Therefore, estimates of the potential cancer risk from CT (and other diagnostic imaging procedures) are based upon studies of 25,000 Japanese atomic bomb survivors and 400,000 radiation workers in the nuclear industry. These studies show a significant increase in the overall cancer risk for radiation exposures in the ballpark of a patient receiving multiple CT scans.

The situation is even clearer for children, who are at greater risk than adults from a given dose of radiation, both because they are inherently more radiosensitive and because they have more remaining years of life during which a radiation-induced cancer could develop.

So far, the authors haven't presented anything too controversial. However, some might find one of their next statements a bit alarming:

On the basis of such risk estimates and data on CT use from 1991 through 1996, it has been estimated that about 0.4% of all cancers in the United States may be attributable to the radiation from CT studies. By adjusting this estimate for current CT use, this estimate might now be in the range of 1.5 to 2.0%.

They conclude:

Although the risks for any one person are not large, the increasing exposure to radiation in the population may be a public health issue in the future.

At this point, I'd like to add a bit of perspective -- a certain amount of radiation exposure is unavoidable. The U. S. Centers for Disease Control estimate that the average dose per person from natural background radiation in the United States is about 3 millisieverts (mSv) per person per year (largely from radon gas).


To put this in further perspective, the additional radiation dosage one gets from a roundtrip airplane flight from New York to Los Angeles is about 0.03 mSv. Doses received from a chest radiograph, an adult abdominal CT and a neonatal abdominal CT are respectively about .1 mSv, 10 mSv and 20 mSv.

Among these exposures, CT certainly stands out, particularly if a given patient needs to undergo several CT's as part of their care.

So, how are radiologists reacting to this study? Quite seriously, as summarized recently by Goske, et al.:

Goske, M.J., Applegate, K.E., Boylan, J., Butler, P.F., Callahan, M.J., Coley, B.D., Farley, S., Frush, D.P., Hernanz-Schulman, M., Jaramillo, D., Johnson, N.D., Kaste, S.C., Morrison, G., Strauss, K.J., Tuggle, N. (2008). The Image Gently Campaign: Working Together to Change Practice. American Journal of Roentgenology, 190(2), 273-274. DOI: 10.2214/AJR.07.3526

There may be disagreement within the medical community about the accuracy of the risk models or the degree to which the risks of radiation were emphasized by the authors. These arguments will not be settled in the near term. However, one fact is indisputable: We must continue our efforts to do a better job of reducing radiation dose to children if and when they need a CT scan.

Goske et al review the ALARA principle (as low as reasonably achievable) and describe recent work by the Alliance for Radiation Safety in Pediatric Imaging, an alliance of 13 major professional organizations. The Image Gently Campaign program by the Alliance is of particular interest.

"One size does not fit all" summarizes much of the Image Gently Campaign, which promotes 4 common sense precepts for pediatric imaging:

1. Reduce or "child-size" the amount of radiation used
2. Scan only when necessary
3. Scan only the indicated region
4. Multiphase scanning is usually not necessary in children

There is no question that CT is an extremely valuable diagnostic imaging tool in both adults and children. It has also been demonstrated quite well that the radiation dose of CT can be minimized in many cases without sacrificing significant image quality. Therefore, even with radiation risks in mind, I would not personally hesitate to have any member of my family undergo a needed CT. Hopefully, the development of sensible risk-reduction programs such as the Image Gently Campaign will help to make this decision easier for other parents as well.