Tag Archives: medical imaging

Photon Counters for CT Scans

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Developments from CERN could make CT scanners even better at detecting early cancer cells or other disease indicators. The facility’s work to create photon counters that can count ten million photons per second – up by a factor of one hundred from previous generation counters – have been integrated into CT systems and had their first trial run with patients. There are more developments that will have to take place before the photon-counters can fullfill their full potential, but early work presented at the meeting looks promising.

While CERN made the progress in photon counter technology, it has been representatives from industry who put them together with CT scanners. At the AIP and AAPM meeting, Reuven Levinson, a Technology Development Leader at GE Healthcare in the CT Engineering group in Haifa, Israel, announced the first use of a photon counting CT system on human patients. The CT’s X-ray detector counts the individual photons and measures their energy. Levinson and his team built the photon counting CT system and had it installed last year at the Rabin Medical Center in Tel Aviv, Israel.

CT scans, introduced in the 1970′s, revolutionized X-rays by giving doctors a sharper look inside their patients. Traditional X-rays can only produce straight on 2D- projection images, while CT scans provide cross sectional slices; revealing internal structures otherwise concealed by overlying layers. In hospitals, CT scans are helpful, and in many cases irreplaceable, in diagnosing diseases and injuries like internal bleeding, strokes, and lung disease. In the US, 68 million CT scans are performed year.

One of the requirements for CT scanning is that the image must be acquired quickly. As with photography, if the patient moves during the scan, the final image will be blurred, so modern CT scanners capture an image in less than 1 second.

These modern CT systems use x-ray detectors, which operate much like digital cameras, with the exception that the CT detectors essentially produce “black and white” photos. The detectors only record the total energy of all the x-rays transmitted through the patient’s body, not the individual energies of each photon. In the optical range, the energy of a photon determines its color, so the CT scanners are in a sense color blind.

And for the most part, CT scanners don’t need to see individual photon energies. For the majority of uses, the black and white photo tells the physician everything they need to know. But in some cases, “color-sensitive” X-ray detectors would be beneficial.

Previous generations of photon counting detectors could count up to only 100,000 x-rays per second, which was not fast enough to produce an adequate CT image.

That was until about five years ago when particle physicists at CERN, the facility in Geneva that is home to the Large Hadon Collider, broke the previous barrier of photon counting by ten orders of magnitude. In need of highly sensitive detectors for their experiments hunting subatomic particles, they increased the capabilities of photon counters to over 10 million photons per second. This increase would allow a photon counter to measure the energy of each individual photon striking the detector from a CT scan.

The results reported by Levinson explained the first use of the photon counting detecor on humans, yet this can not yet assist in detecting specific types of cells. To highlight specific cells that the CT scans can target, the team would like to attach nanoparticles that the photon counter CT system can easily detect – such as gold or other metals – to biomarkers that will attach to the target cells.  So, attaching gold nanoparticles to a peptide that bonds to “vulnerable” plaque cells will illuminate the cells in little gold halos. Another company has reported results using the gold nanoparticles in rats and rabbits.

Eventually the same technology could also be used in cancer detection. While many cancerous tumors are visible on regular CT scanners, there are significant limitations. A CT scanner cannot distinguish between cancer and normal tissue following radiation or chemotherapy treatment.  The imaging of a tumor following the anti-cancer treatment is critical in determining the patient’s status and also in evaluating the efficacy of different treatments in curing the cancer. Current medical practice utilizes PET/CT for the status evaluation of post-treatment cancer patient, which is an expensive and time consuming procedure. The challenge would be for CT plus nanoparticle systems to replace the PET/CT procedure with a simpler, higher resolution and less expensive alternative.

MRI Breast Screenings and Biopsy

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At a meeting with such a heavy emphasis on breast cancer, Debra Ikeda’s talk offered some great information to put all of the new innovations into focus. While most of the speakers were medical physicists working at the cutting edge of technology, Ikeda is a professor of Radiology at Stanford and is working to better define a standard of care for breast MRI and MRI biopsy. So her view of the problem stems from a growing understanding of the biological nature of breast cancer and the problems that face doctors in the field. “I just want to say as a radiologist that I’m very excited to hear about what you guys are working on,” Ikeda said to her fellow presenters.

Breast cancer originates near the root of the milk ducts in the breast, and cancerous cells can move from the ball-shaped root down the ducts.  This early form of breast cancer, known as ductal carcinoma in situ (DCIS), is very difficult to detect.  Later on the cancerous cells can break out of the ducts and become invasive, growing into more recognizable tumors.  While Ikeda promoted MRI treatment, she noted that traditional mammography is actually 25% more effective at identifying this early stage of breast cancer than MRI. 

Most breast cancer patients have their entire breast radiated after the removal of a tumor, to eliminate the risk of the cancer returning through the ducts. Because each breast has multiple ducts, there can be multiple cancer foci in the breast.

Typical tumors usually possess a very high amount of blood vessels. This is one easy to way to spot a tumor – by injecting the patient with a marker or angiogenesis drug, a tumor will uptake the injection faster than the rest of the breast because of the number of blood vessels (although this isn’t always the case).

MRI is more effective than traditional mammography in identifying tumors, especially in high risk patients with dense breast tissue (Ikeda does note, however, that they should be used together, as they both have their advantages). One study of over seven hundred US practices showed that three quarters offer MRI for breast cancer screenings, although the majority of those only do about 5 a week (which is relatively low). 31% percent of those, however, do not do MRI biopsy, which Ikeda believes needs to change. A biopsy is an invasive process that takes tissue samples from an identified abnormality and identifies it as cancer or benign. “It’s important to be able to biopsy when you see something abnormal,” says Ikeda. “It would be horrible to be told ‘You’ve got something…but we can’t biopsy it.’” Ideally of course, methods would increase for discerning between benign lumps in the breast without the need for biopsy.

To more fully understand exactly what physicians will see on MRI scans of different patients, how to look for signs of early cancer, and what standard screening steps to take, Ikeda sits on the BIRAD Lexicon Committee, which constructs the yearly ACR Atlas. The Atlas will compile information to hopefully answer those questions, but it will rely on detailed information from physicians.

The committee’s requests to radiologists include doing bilateral screening in patients (comparing both breasts), comparative studies among patients, and careful descriptions background enhancement.

Background enhancement describes how much of the dense tissue in the breast is enhancing; it’s more of a change in the dense tissue rather than the volume of dense tissue. Background enhancement can change due to natural hormone cycles which can fool an MRI into looking like cancerous tissue Different types of background enhancement filters can better differentiate dense tissue fluctuations.

Four to five percent of women who develop breast cancer will develop it in both breasts, so Ikeda emphasizes the need for doctors to do bilateral care and report their findings. The bilateral studies also make it easier to identify abnormalities in each breast.

As I mentioned before, breast cancer imaging, screening, diagnosis and treatment were discussed in more sessions than perhaps any other topic on the IPF agenda. While the science was all fascinating, this session brought home the human aspect of all the research. It was held in memoriam of Carolyn Kimme-Smith, a leading radiologist in the field of breast cancer study who also suffered from breast cancer. Ikeda began her talk with a quick tribute of her own to Kimme-Smith, saying she was always kind to and respectful of other people, even when their ideas conflicted.