PET-CT



In a Flash
– New dual-source CT sets new speed, dose standards

Siemens Healthcare has introduced a new dual-source CT scanner that set new standards for speed and radiation dose reduction. The new Somatom Definition Flash can perform a complete scan of the entire chest region in just 0.6 seconds and a spiral heart exam with less than 1 millisievert radiation dose. This opens up the possibility of using this scanner in routine cardiac examinations. Middle East Health reports.


 

Siemens presented its new Somatom Definition Flash CT scanner at the 94th Scientific Assembly and Annual Meeting of the Radiological Society of North America (RSNA), in Chicago early December. The new generation dual-source CT scanner, featuring two X-ray tubes and two 128-slice detectors arrays in a single gantry, sets new standards in speed and radiation dose reduction and represents a significant advance in dual source CT technology. The Definition Flash builds on Siemens’ Somatom Definition which first entered the market in 2006.

The high speed of the Somatom Definition Flash offers several advantages, especially regarding examinations of moving structures, such as the thorax and the heart. The gantry rotates about its own axis in just 0.28s (the previous Somatom Definition has a gantry speed of 0.33s). It is this extraordinary rotational speed that enables a scan speed never before attained in CT (i.e., up to 43cm per second) and temporal resolution of 75 milliseconds. The patient is moved through the CT tube more than twice as fast as with any conventional system. At the same time, scans acquired with the Somatom Definition Flash require a much lower radiation dose than conventional scans. While the average effective dose for a heart CT scanner ranges from 8mSv to 40mSv, the new Siemens CT scanner gets by with less than 1mSv. In comparison: the X-ray radiation that everyone is exposed to each year from natural sources amounts to 2mSv to 5mSv. The dose values of the new Siemens CT scanner, thus lie far below those of an intracardiac catheter examination, thus opening up possibilities for using this CT scanner for routine cardiological examinations.

Dr Sami Atiya, Chief Executive Officer of Computed Tomography at Siemens Healthcare said: “The Somatom Definition Flash is not only the world’s fastest CT scanner, but also the one with the lowest radiation exposure. We are proud that our company has once again set a new standard in this regard.”

No breath holds

Due to the high scanning speed, it is now possible to acquire scans of the thorax, the heart or both at the same time in fractions of a second. For example, thorax examinations now only require a scan time of 0.6 seconds. As a result, patients no longer have to hold their breath during the scan. This offers considerable advantages, especially in cases involving the elderly, children, emergency, and ICU patients.

It is also possible to perform whole-body scans extremely fast. For example, a person with a height of 6 feet 6 inches can be scanned in less than 5 seconds. Until now, such whole-body examinations took more than 10 minutes to perform from patient preparation to diagnosis. With the Somatom Definition Flash, this process is completed in just a few minutes. This represents an advantage, especially for emergency medicine since, until now, physicians often had to forego this examination method due to time pressure.

Furthermore, it is no longer necessary to sedate children prior to the examination, since they no longer have to remain still. The high scanning speed also makes it possible to cover large areas measuring up to 48cm with 4D imaging (3D plus time). The areas scannable using conventional systems are limited to a maximum of 16cm due to the detector size involved.

Cardiac examinations


A scan of the entire heart can be performed in only 250 milliseconds, which is less than half a heart beat. In addition, it is possible for physicians to reliably display a heart with a fast pulse or an irregular heart beat without using beta blockers, thus simplifying the workflow and yielding clinical and financial advantages. Owing to its high scanning speed, the Somatom Definition Flash also features new possibilities for performing CT examinations of the heart in the sub-mSv range. This represents a much lower radiation dose than is obtainable with conventional systems, which require doses ranging from 8mSv to more than 40mSv. For the first time ever, the heart can thus be examined at a radiation exposure level that is three times lower than the background radiation a person naturally absorbs in a year. Siemens says the Somatom Definition Flash is the only CT scanner on the market that enables the use of noninvasive cardiological diagnostic techniques as routine applications at the lowest possible radiation exposure levels.

For a triple rule-out exam – performed to rule out coronary artery disease, pulmonary embolism, or aortic dissection in patients presenting with chest pain – the system delivers a dose of less than 5mSv, compared with 15-20mSv for conventional technology.

Double contrast


The second generation of Dual Energy imaging introduces a new imaging quality. The contrast in CT scans can be increased without having to apply the higher radiation dose previously required. This is achieved via a new, selective photon shield which blocks unnecessary parts of the energy spectrum. It thereby provides improved separation of the two simultaneous scans with low and high photon energy, without causing a higher radiation exposure than would result from an individual, conventional CT examination with only one energy source. Thus, the Somatom Definition Flash can always provide a double contrast which, for the first time ever, can also be used to classify the chemical composition of tissues via a CT scan in routine daily work. This will improve clinical applications such as the separation of arteries and bone. Subsequently, it can also be used to reconstruct unenhanced CT images without contrast media and without having to perform an additional examination.

Dose protection

The scanner includes a new Siemens dose reduction technology called X-CARE. This application selectively reduces the radiation exposure of dosesensitive anatomical regions, such as the female breast. This is done by switching the X-ray tube assemblies off during the rotation phase in which the anatomical regions concerned are most directly exposed to radiation. In this way, it is possible to reduce the radiation exposure of individual anatomical regions by up to 40%. Furthermore, an adaptive dose shield blocks irrelevant prespiral and postspiral radiation with dynamic diaphragms, thus ensuring that only a minimum and clinically essential radiation exposure occurs. This enables an additional 25% reduction of the dose required for routine examinations. The CARE Dose4D software, which analyses the individual cross-sectional anatomy in real time and adapts the emitted X-ray dose accordingly, also helps to reduce radiation exposure.

The new CT scanner is expected to be commercially available in the first quarter of 2009. According to Aunt Minnie (www.auntminnie.com) Siemens says the new scanner will carry a list price comparable to other super-premium multislice CT scanners, such as Toshiba’s AquilionOne and GE’s LightSpeed CT750 HD scanner.


PET – a powerful tool for cancer

Recently published data shows that positron emission tomography (PET) led to consistent
changes of treatment in more than 1 out of 3 cancer patients. The study, which surveyed
nearly 41,000 individuals across more than 1,300 sites, is one of the largest studies of its kind and confirms PET as one of the most powerful molecular imaging tools for  diagnosing and fighting cancer. Middle East Health reports.

With the most recent release of data from the United States National Oncologic PET Registry (NOPR), researchers may have reached the moment of critical mass by confirming the effectiveness of positron emission tomography (PET) in the monitoring of tumour activity across a wide range of cancers.

“During the first year of the study, we verified that PET finds more areas of active cancer than other imaging tools and leads, in some cases, to earlier initiation of subsequent treatment,” said Bruce E. Hillner, MD, professor of medicine at Virginia Commonwealth University in Richmond, and lead author of the article. “We noted that PET has a clinically significant impact on cancer management, resulting in a change in treatment in more than one out of three cases – or 36% of the time.”

In the article, published in The Journal of Nuclear Medicine, researchers reported results by cancer type for the first two years of data collected from nearly 41,000 PET studies conducted at more than 1,300 cancer centers in the US. Analysis was restricted to the use of PET for staging, restaging or detection of suspected recurrences in patients with pathologically proven cancers.

Study data released in March 2008 showed a striking consistency of the impact of PET on referring physicians’ intended management plans. At that time, NOPR researchers felt that the significance of the evidence was such that they formally asked the Centers for Medicare and Medicaid Services (CMS) to reconsider the current National Coverage Determination on oncologic use of PET.

“As a result of the data, the follow-up question for the second year was: Does the impact of PET vary between cancers?” explained Hillner. “We found that it did not vary significantly, and that changes in treatment plans for rare cancers – as stomach cancer – clustered around the same onethird mark as the more common cancers. As a result, we believe that coverage for PET in the staging, restaging and detection of recurrence of cancer should be handled the same across the board.”

According to the researchers, a substantial body of national and international literature now exists showing that PET is a highly effective technique for imaging cancer.

“From the data, we concluded that, although the effectiveness of PET may differ somewhat between individual cancers, it’s in the same ballpark,” said Barry A. Siegel, MD, professor of radiology at Mallinckrodt Institute of Radiology in St. Louis and one of the co-authors of the article. “This result was a little unexpected, but leads us to believe that a continual parsing of PET’s usefulness, cancer by cancer and indication by indication, for purposes of reimbursement does not make clinical sense.”

The NOPR was launched in 2006 in response to a proposal from CMS to expand coverage for PET to include cancers and indications not presently eligible for reimbursement, including cancers of the ovary, uterus, prostate, pancreas, stomach, kidney and bladder.

“The NOPR has been a collaborative process with CMS,” said Siegel. “The purpose of our partnership has been to get the best data into the public domain for decisionmaking. We are hopeful that a decade-long process leading to an understanding of the usefulness of PET in cancer management is finally completed.”

A draft decision by CMS is expected on 10 January 2009. Following a 30-day comment period, the final National Coverage Determination will be made 9 April.

● “Relationship of Cancer Type and the Impact of PET and PET/CT on Intended Patient Management: Findings of the National Oncologic PET Registry” Bruce E. Hillner, et al., The Journal of Nuclear Medicine, December 2008.

Cancer management

Meanwhile, in a study conducted at four sites in Australia and comprising 191 patients it was shown that PET changed disease management for more than half of patients with suspected recurrent colorectal cancer. The study was published in the September 2008 issue of The Journal of Nuclear Medicine.

The 191 patients were divided into two groups. Group A consisted of symptomatic patients who had residual structural lesions suspicious for recurrent tumour after initial therapy. Group B comprised patients with pulmonary or hepatic metastases that were potentially operable. These results were compared with findings from conventional imaging (such as computed tomography or CT), and participants were followed for 12 months.

“Designed with an evidencebased approach, this study confirmed the important role PET plays in the decisionmaking process of patients with colorectal cancer and the impact of PET on both the management and outcome of disease,” said Andrew M. Scott, MD, director of the Centre for PET and the Ludwig Institute for Cancer Research, Austin Hospital, Melbourne, Australia. “These results are compelling and indicate that PET should be made more widely available to patients.”

Based on the extent and progression of disease revealed by the scans, treating physicians changed the planned management in more than 65% of patients in group A and nearly 50% in group B. The researchers also found additional disease sites in 48% of group A and 44% in group B, providing valuable prognostic information about patients that allowed their stratification into curative or palliative groups.

“PET was able to identify those patients who had potential for long-term, progressionfree survival and even a potential cure,” said Scott. “Just as important, it identified those patients with aggressive disease, enabling them to avoid unnecessary treatment, such as surgery.”

● “PET Changes Management and Improves Prognostic Stratification in Patients with Recurrent Colorectal Cancer: Results of a Multicenter Prospective Study”, Andrew M. Scott et al, The Journal of Nuclear Medicine, September 2008.


CT rules out appendicitis surgery

CT scans change the initial treatment plans of emergency physicians in over a quarter of patients with suspected appendicitis, according to a study performed at the University of Washington Harborview Medical Center in Seattle, United States and published in the October 2008 issue of the American Journal of Roentgenology.

During the study 100 adult patients admitted to the ER for symptoms of appendicitis were evaluated. The treatment plans of these patients were assessed before and after CT and compared. Results showed that “treatment plans changed in 29% of patients as a result of CT. In many instances, CT ruled out appendicitis when the treatment plan prior to the scan was surgical consultation, eliminating the potential for unnecessary surgery on patients with a normal appendix,” according to Robert O. Nathan, MD, lead author of the study.

“The data suggest that CT can be withheld in patients in whom emergency clinicians rate the likelihood of appendicitis as unlikely, but that CT findings are often of benefit when appendicitis is judged to be very likely,” said Dr Nathan.


GE introduces new PET-CT

GE Healthcare announced the introduction of Discovery PET/CT 600, the company’s newest positron emission tomography/computed tomography (PET/CT) system at the annual meeting of the European Association of Nuclear Medicine (EANM) Congress in Munich in October.

Recently cleared by the US FDA, Discovery PET/CT 600 is optimised for use in oncology, which represents more than 90% of clinical PET/CT exams.

“This new scanner represents a big step in capabilities addressing the biggest clinical challenge in PET/CT, managing and correcting for motion,” said Henry Hummel, general manager of GE Healthcare’s global PET/CT business.

The Discovery PET/CT 600 leverages the high-speed, high-resolution capabilities of GE’s BrightSpeed CT with the breakthrough motion management capabilities of its Discovery PET system. By combining these scanning technologies, the Discovery PET/CT 600 provides the tools to enable physicians to manage disease with more confidence.

As a key component of the image chain, the Discovery PET/CT 600 includes a scintillator with a proven track record and the highest sensitivity in the industry. GE BGO technology enables improved lesion detectability, potentially reducing the dose requirement and allowing for faster scans and increased throughput.

For clinicians, the Discovery PET/CT 600 will provide a large 70cm bore that offers a full 70cm PET and CT Field-of- View and a 225kg patient table. The GE Discovery PET/CT 600 offers an increased vertical scan range that provides more flexibility in radiation treatment planning and patient positioning. 
 


New decision-support software assists dementia diagnosis

              

Philips Research says it has successfully concluded a usability and feasibility study of its decision-support software tool for the automatic evaluation of dementia using PET (Positron Emission Tomography) image data. The software has been evaluated in collaboration with the University Medical Center Hamburg-Eppendorf (Hamburg, Germany) and Austin Hospital (Melbourne, Australia).

Currently, one of the most effective ways of diagnosing dementia in its earlier stages is by performing a PET brain scan with the tracer FDG (Fluorodeoxyglucose). FDGPET is a molecular imaging technique that produces a three-dimensional image of functional processes in the body – in this case, the uptake of glucose that fuels brain activity. However, the interpretation of PET brain-scan images requires a great deal of skill, particularly in the early stages of neurodegenerative disease.

The Philips decision-support software has shown positive results in retrospective studies using libraries of FDG-PET brain-scan images that had already been independently interpreted by an expert. In a study based on a University Medical Center Hamburg- Eppendorf library of FDG-PET scans from 83 patients, the software achieved better than 98% correspondence with the expert physician’s interpretation when programmed to differentiate between brain scans showing no signs of dementia, brain scans characteristic of Alzheimer’s disease and those characteristic of Frontotemporal Dementia.

In a similar 48-patient study using FDG-PET images provided by the Austin Hospital the software achieved better than 80% accuracy in differentiating between the scans of un-diseased patients, those suffering from Alzheimer’s, those suffering from Frontotemporal Dementia and those suffering from Lewy Body Dementia. This so-called 4-class differential diagnosis is more difficult because indications of Alzheimer’s and Lewy Body Dementia occur in similar areas of the brain, while indications of Frontotemporal Dementia appear in a separate area of the brain.

Dementia

Dementia currently affects well over 25 million people worldwide. It is the end result of a number of progressive degenerative diseases of the brain. The most common dementia causing diseases are Alzheimer’s Disease, Lewy-body Dementia and Frontotemporal Dementia – accounting for around 60%, 15% and 10% of all dementia cases respectively. Early differential diagnosis of the type of dementia that a patient is suffering from is essential in order to maximise the benefit of available drugs that can prevent rapid deterioration and subsequent loss in quality of life.

The Philips software analyses PET brain-scan images, and combines them with MRI (Magnetic Resonance Imaging) scans, to detect the characteristic patterns of brain diseases such as Alzheimer’s, Frontotemporal Dementia and Lewy Body Dementia, and then quantifies the degree to which they resemble reference images of known dementia sufferers. The University Medical Center Hamburg-Eppendorf – codeveloper of the system – has been using the software alongside its existing diagnostic procedures for the past year to evaluate its feasibility and usability in a clinical setting.

“The results of the study have been truly excellent,” says Dr Ralph Buchert of the Department of Nuclear Medicine at the University Medical Center Hamburg- Eppendorf. “With most steps performed automatically, operating the software is very straightforward and only adds a couple of minutes to the procedure time. When we made it available to referring physicians who were not skilled in reading FDG-PET and MRI images, they were able to analyse images and interpret the results within a few minutes.”

Dr Henk van Houten, senior vice president Philips Research and head of the Healthcare research programme, said: “Computer-based clinical decision support is regarded as one of the best ways of enabling physicians to optimally use available data and knowledge so that they can consistently deliver evidencebased medicine to their patients in a timely manner.

“Ultimately, such systems will be judged by the people who use them, and that is why it is important to develop this decision support software to aid the diagnosis of dementia in close collaboration with leading dementia research institutes.”



CT perfusion improves fast, accurate stroke diagnosis

Researchers at West Virginia University Health Sciences Center in the United States have shown that CT perfusion imaging may dramatically improve fast and accurate stroke diagnosis, enabling physicians to provide more targeted care and helping avoid potentially lifethreatening complications of “clot buster” therapy. The WVU study is the largest to date of the lifesaving technology’s utility in diagnosing stroke and staging its treatment.

The study, published in the October 2008 issue of The Journal of Emergency Medicine, shows that using CT perfusion to diagnose stroke may be as valuable as magnetic resonance imaging (MRI) – an imaging technology that takes far longer to use at a time when every second counts before treatment is initiated. The CT technology allows physicians to identify patients who are suitable candidates for treatment, utilising either clot busting medicines or clot retrieval devices.

The researchers believe these findings could change protocols on how stroke patients are triaged and potentially extend treatment opportunity beyond the three-to-six hour window.

“Our study reveals that the widespread use of CT perfusion is a practical way to help busy emergency departments save precious time in stroke diagnosis, target treatment and reduce the risks of inappropriate thrombolytic use,” said Ansaar T. Rai, MD, Assistant Professor of Neuro Radiology & Neurointerventional Radiology. “CT perfusion was able to pinpoint strokes with high levels of accuracy, particularly the major intracranial vessel strokes that result in more devastating outcomes.”

Key findings:

● CT perfusion has a very high sensitivity rate – 92% – for detecting infarcts due to a major vessel occlusion, the most debilitating kind of stroke.

● The specificity rate for detecting acute ischemic stroke was perfect – 100%.

The researchers, who have used CT perfusion in clinical practice with the largest reported number of suspected stroke victims of any centre in the US, also report that the average time between emergency room neurological exam and CT scan was 35 minutes.

Under US National Institutes of Health guidelines, hospitals should administer tPA (a clot-busting, or thrombolytic, drug) to patients within a three-hour window of stroke onset. After six hours, the medicine is considered too risky, due to the possibility of a deadly hemorrhage. Just one to two percent of stroke patients receive clot busters. Experts believe this is due largely to perceived risks and uncertainty about whether patients are actually having strokes. A fast, accurate and accessible means of diagnosis of could change these statistics.

Magnetic resonance imaging tests (MRIs) are considered the gold standard for post-stroke analysis, but they are rarely performed and generally impractical because: they take 30 minutes to perform, require a stroke patient to be still to capture clean images, require doctors to check for metal in the patient’s body (which may be impossible if the patient is not verbal) and the MRI units themselves are often understaffed or not located near the emergency room.

CT perfusion offers distinct advantages because most hospital emergency rooms use CT scanners for other purposes, they take one to two minutes to scan, and provide clear images even if a patient cannot lie perfectly still. Most hospitals need only to buy software (at a relatively low cost) to upgrade their systems and institute training programmes. In addition, CT angiograms are necessary to locate blockages and these can be done simultaneously with the perfusion CT, saving valuable time.

■ The WVU study can be viewed online at http://www.sciencedirect.com/, keywords “CT Perfusion”.  



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ate of upload: 25th January 2009

                                  
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