Sunday, May 15, 2011
Friday, May 13, 2011
http://yahoo.brand.edgar-online.com/default.aspx?cik=1416876
Most recent filings and form 3 information.
Friday, April 29, 2011
Medicare to Pay for MRIs in Patients With Pacemakers
WASHINGTON -- The Centers for Medicare & Medicaid Services (CMS) has determined that the evidence is strong enough to reimburse for MRI exams in Medicare patients who have permanent pacemakers.
"We propose to change the language ... of the NCD Manual to remove the contraindication for Medicare coverage of MRI in beneficiaries with implanted PMs [permanent pacemakers] when the PMs are used according to the FDA-approved labeling for use in an MRI environment," the agency's proposed decision memorandum states.
The FDA approved the first MRI-conditional pacemaker (Medtronic Revo MRI SureScan Pacing System) on Feb. 8, but CMS specifically noted that the change in payment policy "does not include any coverage determination about the Medtronic Revo MRI SureScan Pacing System itself or any other pacemaker."
The proposed coverage is not limited to any specific disease or condition.
The new decision broadens one announced on Feb. 24, when CMS said it would cover MRI exams only for patients with pacemakers if they were enrolled in approved clinical studies of MRI.
The next day, CMS received a request letter from Medtronic referencing the randomized controlled trial of 464 pacemaker patients demonstrating the safety of the device in the MR environment and provided CMS with a reference to the journal in which the study was published.
"The requester asked that CMS remove completely the contraindication in the MRI policy for patients with pacemaker devices that have been approved by the FDA for use in the MR environment," according to the CMS decision memorandum.
Following a 30-day public comment period regarding coverage of MRI scans in patients with pacemakers, CMS concluded that "this use of MRI is reasonable and necessary."
"We propose to change the language ... of the NCD Manual to remove the contraindication for Medicare coverage of MRI in beneficiaries with implanted PMs [permanent pacemakers] when the PMs are used according to the FDA-approved labeling for use in an MRI environment," the agency's proposed decision memorandum states.
The FDA approved the first MRI-conditional pacemaker (Medtronic Revo MRI SureScan Pacing System) on Feb. 8, but CMS specifically noted that the change in payment policy "does not include any coverage determination about the Medtronic Revo MRI SureScan Pacing System itself or any other pacemaker."
The proposed coverage is not limited to any specific disease or condition.
The new decision broadens one announced on Feb. 24, when CMS said it would cover MRI exams only for patients with pacemakers if they were enrolled in approved clinical studies of MRI.
The next day, CMS received a request letter from Medtronic referencing the randomized controlled trial of 464 pacemaker patients demonstrating the safety of the device in the MR environment and provided CMS with a reference to the journal in which the study was published.
"The requester asked that CMS remove completely the contraindication in the MRI policy for patients with pacemaker devices that have been approved by the FDA for use in the MR environment," according to the CMS decision memorandum.
Following a 30-day public comment period regarding coverage of MRI scans in patients with pacemakers, CMS concluded that "this use of MRI is reasonable and necessary."
Saturday, April 23, 2011
FDA Clears First MRI-Safe Pacemaker
FDA Clears First MRI-Safe Pacemaker
WASHINGTON -- A cardiac pacemaker that's safe for patients who need an MRI scan has won FDA approval, although the device comes with limitations on which patients and which scans are compatible with it.
The Revo MRI SureScan pacemaker, made by Medtronic, is the first such device to receive marketing clearance in the U.S.
According to the company, the product comes with special leads and other design features that reduce or eliminate certain hazards associated with the MRI environment.
The scanners produce powerful magnetic forces that react with ferric metals and induce electrical currents in electronic components. MRI machines also emit radiofrequency energy that may interact with pacemakers.
As a result, MRI scans can disrupt pacemaker settings or cause wires to overheat, resulting in unintended heart stimulation, device electrical failure, or tissue damage.
Until now, most MRI scans have been contraindicated for patients with pacemakers. About half of such patients have conditions that would ordinarily call for MRI scans, according to the FDA.
Among the features included in the Revo MRI product is a function to be switched on prior to undergoing an MRI to eliminate problems associated with induced currents and radiofrequency emissions.
The FDA's approval rates the device as "MRI-conditional," meaning that it is safe with MRI scans under certain conditions.
Announcements from the FDA and the company didn't indicate specifically what those conditions would be. Medtronic officials did not respond immediately to a request for details.
However, the major clinical trial underpinning the approval -- presented at a meeting in 2009 and published last month -- only tested the device with MRI machines of no more than 1.5 Tesla and the scanning isocenters were located above the cervical spine or below the thoracic spine.
In the trial, 464 patients received the Revo device and were randomized 1:1 to receive an MRI or not. No scan-related complications were seen in patients who had the scans.
The Revo MRI SureScan pacemaker must be used with special leads designed for the system.
The approval was delayed while the company sought to improve conditions at its Mounds View, Minn., manufacturing plant where its pacemakers are produced. The FDA issued a warning letter about the plant in November 2009 and has not yet declared the problems fully resolved.
Medtronic said it is continuing to work with the agency to satisfy its concerns.
http://www.medicalbillingassistanceinc.com/
The Revo MRI SureScan pacemaker, made by Medtronic, is the first such device to receive marketing clearance in the U.S.
According to the company, the product comes with special leads and other design features that reduce or eliminate certain hazards associated with the MRI environment.
The scanners produce powerful magnetic forces that react with ferric metals and induce electrical currents in electronic components. MRI machines also emit radiofrequency energy that may interact with pacemakers.
As a result, MRI scans can disrupt pacemaker settings or cause wires to overheat, resulting in unintended heart stimulation, device electrical failure, or tissue damage.
Until now, most MRI scans have been contraindicated for patients with pacemakers. About half of such patients have conditions that would ordinarily call for MRI scans, according to the FDA.
Among the features included in the Revo MRI product is a function to be switched on prior to undergoing an MRI to eliminate problems associated with induced currents and radiofrequency emissions.
The FDA's approval rates the device as "MRI-conditional," meaning that it is safe with MRI scans under certain conditions.
Announcements from the FDA and the company didn't indicate specifically what those conditions would be. Medtronic officials did not respond immediately to a request for details.
However, the major clinical trial underpinning the approval -- presented at a meeting in 2009 and published last month -- only tested the device with MRI machines of no more than 1.5 Tesla and the scanning isocenters were located above the cervical spine or below the thoracic spine.
In the trial, 464 patients received the Revo device and were randomized 1:1 to receive an MRI or not. No scan-related complications were seen in patients who had the scans.
The Revo MRI SureScan pacemaker must be used with special leads designed for the system.
The approval was delayed while the company sought to improve conditions at its Mounds View, Minn., manufacturing plant where its pacemakers are produced. The FDA issued a warning letter about the plant in November 2009 and has not yet declared the problems fully resolved.
Medtronic said it is continuing to work with the agency to satisfy its concerns.
http://www.medicalbillingassistanceinc.com/
Thursday, April 21, 2011
Airport Scanners: Much Ado About Very Little
Airport body scanners pose no significant radiation threat, even to frequent flyers, who are exposed to far more radiation during travel at high altitudes, authors of a review concluded.
The scanners expose people to less than 1% of the radiation associated with cosmic rays at typical flight altitudes. A single exposure to a backscatter x-ray scanner is equivalent to three to nine minutes of radiation encountered in normal daily living.
Nonetheless, deployment of whole-body scanners at airports should not proceed in the absence of definitive studies to determine more precisely the risks and benefits, according to an article published online in Archives of Internal Medicine.
"In medicine, we try to balance risks and benefits of everything we do, and thus while the risks are indeed exceedingly small, the scanners should not be deployed unless they provide benefit-improved national security and safety -- and consideration of these issues is outside the scope of our expertise," Rebecca Smith-Bindman, MD, and Pratik Mehta, of the University of California San Francisco, wrote in conclusion.
"Issues have been raised regarding the efficacy of scanners, and if the scanners are not deemed efficacious, they should not be used."
On Dec. 25, 2009, a Detroit-bound passenger smuggled plastic explosives aboard an airliner, revealing a limitation of current airport screening devices. Since then the Transportation Security Administration has installed almost 500 whole-body scanners at 78 U.S. airports, and twice that many devices are expected to be in operation by the end of 2011, the authors wrote in their introduction.
Two types of scanners are in use. The millimeter-wave scanner emits low-energy waves estimated as a fraction of the energy emitted by a cell phone. The more commonly used backscatter x-ray scanner emits low-dose x-rays, which are absorbed entirely by the most superficial layers of the skin, the authors continued.
Although the detailed images generated by both types of scanners have raised privacy issues, the potential health risks center on the x-ray scanners, which employ ionizing radiation.
But the radiation doses emitted by the scanners are so low that the potential risks are unknown and difficult to quantify, the authors wrote.
Individuals in the U.S. are exposed to an estimated 6.2 millisieverts of ionizing radiation each year, an amount equivalent to 0.1 microsievert (µSv) per minute, according to the National Council on Radiation Protection and Measurements. The two most common sources of radiation are medical procedures and environmental background radiation.
Backscatter whole-body scanners expose individuals to 0.03 to 0.1 µSv per scan, the equivalent of three to nine minutes of radiation from natural sources.
Levels of naturally occurring radiation are increased at higher altitudes, such as those used by airliners. Although the levels change with altitude, radiation exposure during a flight averages about 0.04 µSv per minute of flight time. Thus, backscatter x-ray scanners deliver an amount of radiation equivalent to one to three minutes of flight time.
"Put into context of the entire flight, if a woman embarks on a six-hour flight, she will be exposed to approximately 14.3 µSv of radiation from the flight and 0.03 to 0.1 µSv from passing through the scanner at the airport," the authors wrote. "Thus, the scan will increase her exposure by less than 1%."
Given those calculations, concerns that vulnerable individuals should avoid the scanners are unwarranted, they added.
Offering other common examples for context, Smith-Bindman and Mehta noted that a person would have to pass through an airport scanner 50 times to get the same radiation exposure associated with a single dental x-ray, 1,000 times to equal the exposure of a chest x-ray, 4,000 times to equal the exposure of a mammogram, and 200,000 times to equal the exposure of a single combination abdominal-pelvic CT scan.
Estimating the cancer risk associated with airport scanners is even more difficult than quantifying the exposure, the authors continued.
Risk estimates normally rely on extrapolation from published studies of higher-dose exposures. Such extrapolation from the scanners' exceedingly small radiation doses is questionable and perhaps inappropriate.
Radiation exposure from the scanners is concentrated in the skin. No accepted mathematical models exist for determining the relationship between skin exposure and the risk of skin cancer. Moreover, the distribution of exposure differs from that of the whole-body exposure assumed by available mathematical models.
Noting that 100 million people have a total of 750 million flights per year, Smith-Bindman and Mehta estimated that radiation exposure from airport scanners would cause six excess cancers.
In contrast, 40 million cancers would be expected over the same individuals' lifetimes.
Frequent flyers represent one population potentially vulnerable to radiation exposure from airport scanners. Assuming one million of these passengers take 10 six-hour trips per week for a year, airport scanners would cause four cancers.
That compared with an estimated 600 excess cancers from radiation exposure during the flights and 400,000 cancers over the passengers' lifetimes.
Young children who fly frequently are another potentially vulnerable population. Using a five-year-old girl as an example, the authors estimated that two million girls flying once a week would have one excess breast cancer. In contrast, 250,000 of the girls will develop breast cancer over their lifetimes owing to the 12% lifetime risk of the disease.
"Based on what is known about the scanners, passengers should not fear going through the scans for health reasons, as the risks are truly trivial," the authors wrote in conclusion.
"If individuals feel vulnerable and are worried about the radiation emitted by the scans, they might reconsider flying altogether since most of the small, but real, radiation risk they will receive will come from the flight and not from the exceedingly small exposures from the scans."
http://www.medicalbillingassistanceinc.com/
The scanners expose people to less than 1% of the radiation associated with cosmic rays at typical flight altitudes. A single exposure to a backscatter x-ray scanner is equivalent to three to nine minutes of radiation encountered in normal daily living.
Nonetheless, deployment of whole-body scanners at airports should not proceed in the absence of definitive studies to determine more precisely the risks and benefits, according to an article published online in Archives of Internal Medicine.
"In medicine, we try to balance risks and benefits of everything we do, and thus while the risks are indeed exceedingly small, the scanners should not be deployed unless they provide benefit-improved national security and safety -- and consideration of these issues is outside the scope of our expertise," Rebecca Smith-Bindman, MD, and Pratik Mehta, of the University of California San Francisco, wrote in conclusion.
"Issues have been raised regarding the efficacy of scanners, and if the scanners are not deemed efficacious, they should not be used."
On Dec. 25, 2009, a Detroit-bound passenger smuggled plastic explosives aboard an airliner, revealing a limitation of current airport screening devices. Since then the Transportation Security Administration has installed almost 500 whole-body scanners at 78 U.S. airports, and twice that many devices are expected to be in operation by the end of 2011, the authors wrote in their introduction.
Two types of scanners are in use. The millimeter-wave scanner emits low-energy waves estimated as a fraction of the energy emitted by a cell phone. The more commonly used backscatter x-ray scanner emits low-dose x-rays, which are absorbed entirely by the most superficial layers of the skin, the authors continued.
Although the detailed images generated by both types of scanners have raised privacy issues, the potential health risks center on the x-ray scanners, which employ ionizing radiation.
But the radiation doses emitted by the scanners are so low that the potential risks are unknown and difficult to quantify, the authors wrote.
Individuals in the U.S. are exposed to an estimated 6.2 millisieverts of ionizing radiation each year, an amount equivalent to 0.1 microsievert (µSv) per minute, according to the National Council on Radiation Protection and Measurements. The two most common sources of radiation are medical procedures and environmental background radiation.
Backscatter whole-body scanners expose individuals to 0.03 to 0.1 µSv per scan, the equivalent of three to nine minutes of radiation from natural sources.
Levels of naturally occurring radiation are increased at higher altitudes, such as those used by airliners. Although the levels change with altitude, radiation exposure during a flight averages about 0.04 µSv per minute of flight time. Thus, backscatter x-ray scanners deliver an amount of radiation equivalent to one to three minutes of flight time.
"Put into context of the entire flight, if a woman embarks on a six-hour flight, she will be exposed to approximately 14.3 µSv of radiation from the flight and 0.03 to 0.1 µSv from passing through the scanner at the airport," the authors wrote. "Thus, the scan will increase her exposure by less than 1%."
Given those calculations, concerns that vulnerable individuals should avoid the scanners are unwarranted, they added.
Offering other common examples for context, Smith-Bindman and Mehta noted that a person would have to pass through an airport scanner 50 times to get the same radiation exposure associated with a single dental x-ray, 1,000 times to equal the exposure of a chest x-ray, 4,000 times to equal the exposure of a mammogram, and 200,000 times to equal the exposure of a single combination abdominal-pelvic CT scan.
Estimating the cancer risk associated with airport scanners is even more difficult than quantifying the exposure, the authors continued.
Risk estimates normally rely on extrapolation from published studies of higher-dose exposures. Such extrapolation from the scanners' exceedingly small radiation doses is questionable and perhaps inappropriate.
Radiation exposure from the scanners is concentrated in the skin. No accepted mathematical models exist for determining the relationship between skin exposure and the risk of skin cancer. Moreover, the distribution of exposure differs from that of the whole-body exposure assumed by available mathematical models.
Noting that 100 million people have a total of 750 million flights per year, Smith-Bindman and Mehta estimated that radiation exposure from airport scanners would cause six excess cancers.
In contrast, 40 million cancers would be expected over the same individuals' lifetimes.
Frequent flyers represent one population potentially vulnerable to radiation exposure from airport scanners. Assuming one million of these passengers take 10 six-hour trips per week for a year, airport scanners would cause four cancers.
That compared with an estimated 600 excess cancers from radiation exposure during the flights and 400,000 cancers over the passengers' lifetimes.
Young children who fly frequently are another potentially vulnerable population. Using a five-year-old girl as an example, the authors estimated that two million girls flying once a week would have one excess breast cancer. In contrast, 250,000 of the girls will develop breast cancer over their lifetimes owing to the 12% lifetime risk of the disease.
"Based on what is known about the scanners, passengers should not fear going through the scans for health reasons, as the risks are truly trivial," the authors wrote in conclusion.
"If individuals feel vulnerable and are worried about the radiation emitted by the scans, they might reconsider flying altogether since most of the small, but real, radiation risk they will receive will come from the flight and not from the exceedingly small exposures from the scans."
http://www.medicalbillingassistanceinc.com/
Thursday, April 14, 2011
MRI Volume Loss May Foretell Alzheimer's
Individuals with certain signatures on MRI scans are at greatly increased risk of developing Alzheimer's disease, according to two independent studies.
In one, cognitively normal adults with low cortical thickness parameters characteristic of Alzheimer's disease went on to develop the disease at a 55% rate, compared with 0% among similar people with higher-than-average cortical thickness (P<0.005).
The other study showed that similar MRI-based measurements could predict which patients with mild cognitive impairment would progress to full-blown Alzheimer dementia during the following year, with an odds ratio of 7.2 (P not reported) comparing the highest with the lowest quartiles of cortical volume scores.
The authors of both studies concluded that, in many patients who develop Alzheimer's disease, their brains show physical changes characteristic of the condition long before clinical symptoms qualify them for a diagnosis.
In fact, according to the first study, published online in Neurology, those changes were detectable in apparently healthy people as much as 11 years before diagnosis.
Brad Dickerson, MD, of Massachusetts General Hospital in Boston, and colleagues performed MRI scans in two independent samples of cognitively normal adults in their late 60s and 70s.
The first sample included eight people who went on to receive an Alzheimer's diagnosis a mean of 11.1 years later and 25 whose cognitive performance remained normal. In the second sample, 32 cognitively normal individuals were scanned, including seven who converted to Alzheimer's disease after a mean of 7.1 years.
Ten brain regions were scanned to produce a composite cortical thickness score, measured in millimeters. In both groups, those who went on to develop Alzheimer's disease had scores that were about 0.2 mm lower than participants remaining cognitively normal (P<0.05), Dickerson and colleagues reported.
Also, for each standard deviation of cortical thickness score relative to the mean, the hazard ratio for developing Alzheimer's disease was 3.4 (P<0.0005), the researchers indicated.
The second study was published online in Neuroradiology by Linda McEvoy, PhD, of the University of California San Diego, and colleagues. They performed MRI scans in 203 normal controls, 164 people with mild Alzheimer's disease, and 317 with mild cognitive impairment, all with mean ages of about 75.
As in the study by Dickerson and colleagues, MRI measures of different cortical regions were combined into an overall score. Scores for the cognitively normal and Alzheimer's disease groups were then incorporated into a model applied to the participants with mild cognitive impairment.
In the latter group, nearly 90% had at least 18 months of follow-up. The average one-year rate of conversion to Alzheimer's disease in patients with mild cognitive impairment was 17%.
Among patients in the highest quartile of risk according to the baseline MRI scans, the one-year conversion rate was 40%, versus 3% in the lowest quartile, McEvoy and colleagues reported.
The study also included a second set of MRI scans performed one year after the baseline scans, the researchers indicated. After excluding patients who did not complete a full year of follow-up after the second round of scans or who had converted to Alzheimer's disease during the first year, the analysis covered 170 participants with mild cognitive impairment.
When these results were incorporated into the risk-prediction model, the highest-risk participants with mild cognitive impairment converted to Alzheimer's disease at a one-year rate of 69%, compared with 3% among the lowest-risk participants (odds ratio 12.0, P=0.001).
McEvoy and colleagues acknowledged that predicting which individuals would progress to Alzheimer's disease would have limited clinical value in the absence of treatments that can halt or delay the process.
On the other hand, they wrote, "such predictive prognostic information will be critical if disease-modifying therapies become available."
For their part, Dickerson and colleagues said their findings suggest that MRI markers should be included in research criteria now being developed for so-called preclinical Alzheimer's disease.
Again, although such a designation would have little clinical relevance at present, the research community is eager for a standard, objective definition that could be used to recruit participants for trials of disease-modifying therapies aimed at preventing onset of clinical symptoms.
Both groups of authors indicated that their studies were limited by uncertainties in the baseline characterizations of patients as cognitively normal and in the clinical diagnoses. Additionally, the Neurology study had relatively small sample sizes, whereas McEvoy and colleagues noted that their samples were not representative of the general clinical population.
Also, neither study reported standard diagnostic accuracy measures such as sensitivity, specificity, or positive/negative predictive values for their risk scoring systems.
http://www.mediaclbillingassistanceinc.com/
In one, cognitively normal adults with low cortical thickness parameters characteristic of Alzheimer's disease went on to develop the disease at a 55% rate, compared with 0% among similar people with higher-than-average cortical thickness (P<0.005).
The other study showed that similar MRI-based measurements could predict which patients with mild cognitive impairment would progress to full-blown Alzheimer dementia during the following year, with an odds ratio of 7.2 (P not reported) comparing the highest with the lowest quartiles of cortical volume scores.
The authors of both studies concluded that, in many patients who develop Alzheimer's disease, their brains show physical changes characteristic of the condition long before clinical symptoms qualify them for a diagnosis.
In fact, according to the first study, published online in Neurology, those changes were detectable in apparently healthy people as much as 11 years before diagnosis.
Brad Dickerson, MD, of Massachusetts General Hospital in Boston, and colleagues performed MRI scans in two independent samples of cognitively normal adults in their late 60s and 70s.
The first sample included eight people who went on to receive an Alzheimer's diagnosis a mean of 11.1 years later and 25 whose cognitive performance remained normal. In the second sample, 32 cognitively normal individuals were scanned, including seven who converted to Alzheimer's disease after a mean of 7.1 years.
Ten brain regions were scanned to produce a composite cortical thickness score, measured in millimeters. In both groups, those who went on to develop Alzheimer's disease had scores that were about 0.2 mm lower than participants remaining cognitively normal (P<0.05), Dickerson and colleagues reported.
Also, for each standard deviation of cortical thickness score relative to the mean, the hazard ratio for developing Alzheimer's disease was 3.4 (P<0.0005), the researchers indicated.
The second study was published online in Neuroradiology by Linda McEvoy, PhD, of the University of California San Diego, and colleagues. They performed MRI scans in 203 normal controls, 164 people with mild Alzheimer's disease, and 317 with mild cognitive impairment, all with mean ages of about 75.
As in the study by Dickerson and colleagues, MRI measures of different cortical regions were combined into an overall score. Scores for the cognitively normal and Alzheimer's disease groups were then incorporated into a model applied to the participants with mild cognitive impairment.
In the latter group, nearly 90% had at least 18 months of follow-up. The average one-year rate of conversion to Alzheimer's disease in patients with mild cognitive impairment was 17%.
Among patients in the highest quartile of risk according to the baseline MRI scans, the one-year conversion rate was 40%, versus 3% in the lowest quartile, McEvoy and colleagues reported.
The study also included a second set of MRI scans performed one year after the baseline scans, the researchers indicated. After excluding patients who did not complete a full year of follow-up after the second round of scans or who had converted to Alzheimer's disease during the first year, the analysis covered 170 participants with mild cognitive impairment.
When these results were incorporated into the risk-prediction model, the highest-risk participants with mild cognitive impairment converted to Alzheimer's disease at a one-year rate of 69%, compared with 3% among the lowest-risk participants (odds ratio 12.0, P=0.001).
McEvoy and colleagues acknowledged that predicting which individuals would progress to Alzheimer's disease would have limited clinical value in the absence of treatments that can halt or delay the process.
On the other hand, they wrote, "such predictive prognostic information will be critical if disease-modifying therapies become available."
For their part, Dickerson and colleagues said their findings suggest that MRI markers should be included in research criteria now being developed for so-called preclinical Alzheimer's disease.
Again, although such a designation would have little clinical relevance at present, the research community is eager for a standard, objective definition that could be used to recruit participants for trials of disease-modifying therapies aimed at preventing onset of clinical symptoms.
Both groups of authors indicated that their studies were limited by uncertainties in the baseline characterizations of patients as cognitively normal and in the clinical diagnoses. Additionally, the Neurology study had relatively small sample sizes, whereas McEvoy and colleagues noted that their samples were not representative of the general clinical population.
Also, neither study reported standard diagnostic accuracy measures such as sensitivity, specificity, or positive/negative predictive values for their risk scoring systems.
http://www.mediaclbillingassistanceinc.com/
Saturday, April 9, 2011
MRI value in cardiac arrest
In the past year, three studies have been published evaluating the use of magnetic resonance imaging (MRI) to determine the prognosis of patients suffering out-of-hospital cardiac arrest, a leading cause of death in developed countries [1-3]. The initial survival of these patients has improved recently thanks to the increased availability of automated defibrillators and induced hypothermia [4,5], leading to an increasing number of patients hospitalized with post-anoxic coma. However, survival rates without major neurological sequelae remain low, and intensive care must be withdrawn in a significant number of patients who will otherwise evolve to a vegetative or minimally conscious state. This decision is currently based on clinical data. Lack of motor response at 24 and 72 hours, absent corneal reflex and pupillary response at 24 hours have been shown to be indicative of poor clinical outcome [6]. This approach, however, has many limitations. While it can reliably predict a poor clinical outcome, prediction of good clinical evolution is still difficult. Among patients with a good clinical outcome, it is impossible to separate those who will have a complete recovery (restitutio ad integrum) from those whose quality of life will be hampered by significant neurological sequelae. Clinical examination can provide variable results and is not compatible with the deep sedation required by some therapeutic protocols, especially hypothermia.
MRI is now widely available, and, with some precautions, can be performed in patients under mechanical ventilation. Despite the fact that MRI with diffusion-weighted imaging (DWI) has been shown to efficiently detect anoxo-ischemic brain injury (especially in stroke), its application for the evaluation of cardiac arrest patients had not been developed until very recently. Three recent papers attempt to address this issue.
In Critical Care, Choi and colleagues [1] have shown in a series of 39 survivors of cardiac arrest that the presence of lesions in both the cortex and basal ganglia on DWI was strongly associated with a poor outcome. Moreover, they could determine cut-off values of the apparent diffusion coefficient (ADC; quantitative data that can be extracted from the DWI sequence) that could predict this outcome with 100% specificity. Clinical decisions can thus be made based on both reliable quantitative information and images that are useful for explaining the situation to the patient's family. Wijman and colleagues [2] have shown that brain volume with ADC values below certain thresholds correlated with clinical outcome with a better sensitivity than clinical examination. A study by Wu and colleagues [3] basically combined these two approaches and found similar results.
While promising, these three studies share some limitations. They all included a limited number of patients. Due to the rapid time-dependant variations of ADC, MRI can only be performed early (2 to 5 days) after the cardiac arrest, during a period when performing this examination is potentially associated with a significant risk, since patients might still require catecholamine. Cut-off values can predict a poor outcome with perfect specificity but less than perfect sensitivity, meaning that, as with clinical examination, while the presence of lesions with a reduced ADC beyond a defined threshold is strongly suggestive of a poor outcome, a significant number of subjects with a 'good' MRI will also still have a poor outcome. They also share the risk that, if the clinicians were not fully blinded to the result of the MRI, some clinical decisions could have been based on the results of the scan, leading to so-called 'self-fulfilling prophecies'. Finally, all these studies were monocentric. While ADC was initially supposed to be a physical characteristic of the tissue, significant variations in its measurement have been reported, depending on the MRI device [7]. These results must thus be confirmed and improved in a multicentric study designed to correct machine dependant variations. If such a study should be performed, introduction of other MRI parameters, such as fractional anisotropy and spectroscopy, might certainly be relevant.
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