Siemen’s Biograph mMR

Molecular Imaging

June 26, 2014

Molecular imaging is an ever-changing field as new imaging technologies emerge and take over some, or all the turf of the previous modalities. Right now, this is in somewhat of a holding pattern as researchers and clinicians conduct further investigation into PET/MR’s usefulness.

PET/MR started solely as a research modality, but it’s beginning to creep into the clinical setting and so the question now arises as to whether it can perform certain applications better than PET/CT.

Many challenges still stand in the way of the modality gaining widespread adoption so for now it poses little threat to PET/CT. Nevertheless, PET/CT is still continuing to make some notable strides.

On the opposite side of the spectrum, SPECT, an older modality, seems to still be on people’s minds even though newer imaging technologies have captured the limelight. Just like PET/MR, experts have mixed opinions about what place SPECT has in the future.

PET/MR has its benefits and challenges
What makes PET/MR so attractive is its superior soft-tissue contrast and lower radiation dose over PET/CT. “For certain applications we may move away from PET/CT to PET/MR and that is really going to be another big revolution in medical imaging,” says Dr. Abass Alavi, professor of radiology at the Hospital of the University of Pennsylvania (Alavi also sits on the editorial advisory board for DOTmed HealthCare Business News).

Researchers from University Hospitals Case Medical Center have investigated those applications and have published their findings in the September issue of Current Radiology Reports in an article titled “PET/MRI: Applications in Clinical Imaging.”

They collaborated with Philips Healthcare, using their Ingenuity TF PET/MR, and found that PET/MR is particularly promising for oncologic applications, and provides added value in the diagnosis, staging and treatment planning of colorectal, cervical, uterine, ovarian, and pancreatic cancers and also provides strong support for the diagnostic management of children and young adults.

“The initial focus of our experiences with this new hybrid modality, worldwide, was gained in the field of oncologic imaging,” says Dr. Karin Herrmann, one of the researchers.

However, Herrmann adds that the research is still ongoing and they are continuing to investigate where the modality is helpful. There are currently three PET/MR models on the market today sold by Siemens Healthcare, GE Healthcare and Philips Healthcare. However, Siemens’ Biograph mMR is the only vendor to offer a whole body and fully integrated PET and MR scanner that performs simultaneous imaging.

Philips’ Ingenuity TF PET/MR involves a separate PET scanner and MR scanner positioned on each end of a patient table in the same room. GE has a trimodality system, in which the Discovery PET/CT 690 and Discovery MR 750 are situated in adjacent rooms and the patient is transferred with a detachable patient table.

GE currently has nine trimodality systems installed globally. The University Hospital in Zurich decided to purchase the system because at the time, fully integrated PET/MR was not mature and they wanted to avoid any technical problems associated with the integration of MR and PET including attenuation correction, surface coil attenuation and metallic implants, according to Dr. Gustav von Schulthess, professor and chairman of the department of medical radiology at the hospital.

But other facilities prefer the fully integrated system. Siemens has sold more than 50 of their systems worldwide and says it’s primarily used for oncologic applications, but neurologic and cardiac applications also come into play.

Siemens says it is noticing a shift with PET/MR moving into the clinical arena. “Of course, the early adopters will be at the academic centers that are looking to use the technology in novel ways — for cancer treatment response, neuroscience using novel tracers and dynamic simultaneous PET and MRI — and still there’s significant interest in that area,” says Abram Voorhees, business manager of the Biograph mMR at Siemens. “Now we are seeing a trend towards adopters that will use the system clinically.”

Along with the academic medical centers, Zwanger-Pesiri Radiology and Golisano Children’s Hospital in New York and Hoag Neurosciences Institute in California have installed systems for clinical use.

Washington University School of Medicine in St. Louis purchased PET/MR a little less than three years ago and they are now getting to the point where they’re ready to use it clinically—mainly for dementia and pelvic cancer research, but also more recently for cardiac imaging.

They will also use it on children and adolescents once they get all the “bugs worked out of the clinical operations,” says Dr. Robert McKinstry, a radiologist at the university.

PET/MR is particularly promising for that population because it emits less radiation than PET/CT. “The reduced dose is likely to have significant impact over the course of their lifetime,” says McKinstry.

Even though it has to undergo a few technical innovations first, McKinstry believes that in the next five to 10 years PET/MR will become just as popular as PET/CT. “I think there are many areas where it will be the go-to exam over PET/CT,” he says. “In five to 10 years, I do think we’ll have it down so you could have just one PET/MR in your practice, I think that will be possible.”

One of the big hurdles thought to stand in PET/MR’s way was the fact that there was no dedicated PET/MR CPT code for reimbursement. But that changed last June when CMS, in response to a request from the National Oncologic PET Registry, issued a decision memo both expanding coverage and clarifying its position on PET/ MR by including FDG PET/MR in their definition of FDG PET.

“In light of this decision, our customers are building business models based on established PET and MR indications, facilitating clinical adoption of the technology where it makes the most sense for the patient,” says Siemens’ Voorhees. Even though research is showing that PET/MR has promise in certain applications and it’s starting to come into the clinical setting, many experts are still critical of it.

“I don’t think it’s going to be something that you’re going to see proliferating like how PET/CT was proliferating initially into the community,” says Dr. Hossein Jadvar, president of the Society of Nuclear Medicine and Molecular Imaging’s PET Center of Excellence and vice president-elect of the society. “I don’t think this is going to happen like that — it’s going to take much longer.”

Its high capital cost is one of its turn-offs. “When it comes back to the cost of MRI — they’re selling for five million dollars-plus, but PET/CT is only two million dollars,” says University of Pennsylvania’s Alavi.

Additionally, hospitals want to know that they will make the money back after purchasing it. “People should be able to buy the device and should be able to in a reasonable amount of time, pay for the initial investment and get paid for those studies,” says Jadvar.

Even though CMS is including FDG PET/MR in its definition of FDG PET, Jadvar questions if they will pay significantly above PET/ CT so that hospitals will be able to justify the purchase of such an expensive machine.

Another drawback is the amount of time it takes to acquire an image. A whole body CT scan takes about 20 to 30 seconds, but an MR scan can take up to an hour.

But Herrmann and her fellow researchers are working to solve that problem. “We are improving and optimizing the process of developing appropriate imaging protocols so that we can perform the two exams within a reasonable amount of time and with the benefit of a better diagnosis,” she says.

A big question that is not answered right now is — who should be interpreting the exams? Should it be the radiologist, nuclear medicine physician or MRI technologist?

Jadvar says he and other doctors are starting to address the question. He is currently co-chairman of the SNMMI-ACR Joint Task Force of PET/MRI Credentialing, which is attempting to come up with that guideline for brain PET/MR interpreters.

All of these challenges need to be ironed out before PET/MR can enjoy the same success that PET/CT has. “There are multi-faceted things that are going on in here and it takes time for all of them to be aligned in a way that you will see PET/MR as a reality out there that people want,” says Jadvar.

PET/CT will still dominate
Most of the experts interviewed for this story agree that PET/MR will never replace PET/CT. “The purpose of this new imaging modality is not to replace PET/CT, there is no sense in replacing a modality that is working well and that has been established for almost 20 years now for certain indications,” says Herrmann.

Market forecast reports even prove that PET/CT will still experience significant growth in the coming years. The Advisory Board Company projected in May 2012 that PET/CT will grow 22 percent over the next five years and 55 percent over the next 10 years and technological advances are one of the main drivers.

One of the most recent advances is GE’s new Q.Clear technology. The technology uses the regularized reconstruction iterative algorithm, as opposed to the conventional ordered subsets expectation maximization algorithm. GE says that the new algorithm improves PET quantitation accuracy and image quality up to two times.

One of the disadvantages of OSEM is that it generally can’t run to full convergence because the noise of the image grows with each iteration. In order to compensate for that in clinical use, the algorithm is usually stopped after a few iterations to provide a decent contrast recovery at an acceptable noise. But the result is an under-converged image with standard uptake value quantitative bias, which impacts the lesion quantitation.

“The breakthrough that Q.Clear introduces is to take away that compromise,” says Wei Shen, global PET/CT general manager at GE. “It’s a new method that can suppress the noise level as it converges so you can get to a very clear image to read from, as well as a very good fully convergent measurement that you can also trust.”

It’s currently available for the Discovery PET/CT 710 premium configuration but GE’s goal is to have it across all of their production products, as well as the recent portions of the installed base in the future.

Accurate quantitation is becoming more important now that clinicians are using PET not only for diagnosing and staging a disease but also for treatment monitoring. “We definitely see that to be the trend that it’s not just used in the early part of the pathway, but also throughout the entire continuum — for staging, restaging, as well as treatment assessment,” says Shen.

When GE spoke with their customers, the feedback they received was that Q.Clear helps them see the image more clearly and it gives them more confidence in their diagnosis. “They’re always using a lot of information at their disposal to make the diagnosis, but having an image that is clearer and a number that is more trustworthy helps the clinicians to be more confident and read through the images faster,” says Shen.

Philips is also making strides in the field. At RSNA 2013, they unveiled their new Vereos PET/CT and they claim it’s the world’s first and only digital PET/CT. They say that compared to analog, digital PET technology provides two times improved volumetric resolution, sensitivity gain and improved quantitative accuracy.

Their digital photon counting technology converts scintillation light directly to a digital signal. According to Philips, the one-to-one ratio coupling of crystals-to-light sensors results in a linear count rate, faster time-of-flight performance and overall better sensitivity compared to analog.

Meanwhile, Siemens launched their latest PET/CT, Biograph mCT Flow, last June at the SNMMI annual meeting. It’s powered by their FlowMotion technology and they claim it’s the world’s first PET/CT system that eliminates the need for stop-and-go imaging.

In other systems, a scan is done with sequential static acquisitions so the table moves to a certain position, stops and acquires the data, then moves to a different position for further acquisition and repeats the process until the procedure is finished. For Siemens’ system, the patient moves through the gantry and continuously obtains PET data.

What’s SPECT’s fate?
Even though these shiny, new modalities have stolen some of the spotlight from SPECT, it still might have a place in the future market. SNMMI’s Jadvar believes that SPECT and SPECT/CT will be around for a long time because not every country’s health system has the money to purchase more expensive imaging technologies.

“People think more of the U.S. market but around the world, SPECT is still very important and it will continue to be important for a long, long time because not every country on the planet is going to have a PET scanner,” he says.

Additionally, there are some questions that can be answered without a PET scanner. Jadvar believes that there are a lot of cases that “can be answered just fine with tracers that have a long legacy and history.”

What may be surprising to some is that new SPECT cameras are still continuing to infiltrate the market. For example, the MultiCam 3000eco, a SPECT system envisioned by Eclipse and manufactured by InterMedical, just received FDA approval. It was designed and manufactured for brain imaging, but it can also be used for cardiac imaging — something SPECT has been good at for a long time.

The Denmark-based company, DDD-Diagnostic A/S, recently received FDA approval for its QuantumCam SPECT camera, just in time for this year’s SNMMI meeting. Universal Medical Resources Inc. (UMRi), a Missouri-based company that sells refurbished and new nuclear medicine equipment, is the primary distributor of DDDDiagnostic equipment in North America.

Compared to other SPECT cameras on the market, the company says that QuantumCam has lower acquisition and ownership cost, a smaller footprint and higher quality. “It’s hard to find all of these attributes in one device,” says Jason Kitchell, chief operating officer at UMRi.

Kitchell doesn’t think that SPECT and PET/CT compete with each other since each modality has different attributes. He compares it to MR, CT and SPECT—“Each brings its own attributes to the table and is not always so easily compared,” he says.

But not everyone agrees. University of Pennsylvania’s Alavi says that the reason why people moved away from SPECT is because it can’t label biologically important compounds including glucose, dopamine and amino acid. But those radioactive elements can be used very well with PET.

“Sooner or later it has to go,” says Alavi. “SPECT cannot do what PET can do from many, many points of view.”

Myocardial perfusion imaging was primarily done with SPECT but now it’s starting to shift toward PET. When the Canadian Chalk River nuclear reactor in Ontario shutdown in 2009, it led to a shortage of technetium-99m, which is the primary radiotracer used in SPECT heart scans.

Many cardiology practices have already started to use PET instead of SPECT with rubidium-82, which is used in over 90 percent of cardiac PET scanning. But it has drawbacks – its half life is 75 seconds, its supply is unstable and there have recently been safety concerns regarding it.

New radiopharmaceuticals are starting to enter the field including N-13 ammonia, which has been around for a while, but soon it will be available on a larger scale for PET heart scans. N-13 ammonia’s competitor, flurpiridaz F-18, is also on its way.

Both have a reputation for producing good image quality with quantitative regional flow, which means the images are easier to read and the data is cleaner. But so far, flurpiridaz has only been used on about 900 subjects with more studies in the works, so right now its full impact is yet to be determined.

Even though PET comes with a much higher price tag than SPECT, Alavi still believes that it’s worth the money. “If you have a cheaper [system] that is only accurate 60 percent of the time, you are defeating yourself by not diagnosing that 40 percent that is going to kill the patient and cost society more money at the end,” he says.

Furthermore, he says the newer SPECT/CT is not a permanent fix and is just “patching the hole” until SPECT disappears. But only time can really tell what the future holds for SPECT and whether or not PET/MR will enjoy the same success that PET/CT has.

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