Posts Tagged ‘Siemens Healthcare’

Acute and Chronic Myocardial Infarction: Quantification of Myocardial Perfusion Viability – FDG-PET/MRI vs. MRI or PET alone

Author, and Content Consultant to e-SERIES A: Cardiovascular Diseases: Justin Pearlman, MD, PhD, FACC


Reporter: Aviva Lev-Ari, PhD, RN

The Voice of  Justin Pearlman, MD, PhD, FACC

While working on angiogenesis imaging support at Harvard, the author discovered that injured heart muscle retains gadolinium-based contrast used for perfusion testing (1992). Whereas the gadolinium passes through normal tissue in less than 20 minutes and redistributes mostly to body fat, it stays where cell membranes are damaged, even if the damage is old. The gadolinium then “lights up” the damaged zone when normal heart muscle tissues appear dark by magnetic resonance imaging (MRI). Thus “scar mapping” was born. Prior to that discovery, the standard test for “viability” was a positron emission tomography (PET) scan reporting the presents of absence of normal sugar metabolism in damaged or ischemic heart muscle. PET relies on detection of a pair of gamma rays emitted by a radioactive label in a metabolite. The pair are emitted simultaneously at nearly 180 degrees apart, with a small angulation offset from the momentum of the emitter. The emission event requires a positron finds an electron, so it does not occur precisely where the metabolite sits, and thus has inherently a poor “resolution” (minimal distance where two distinct sources are identifiable as distinct).  The protocol for PET assessment of heart muscle viability utilized by the author and other investigators required intravenous infusion of glucose, insulin, and potassium, to assure good delivery of sugar to the healthy viable heart muscle, coupled to repeat blood tests to make sure the blood sugar and serum potassium levels were adequately maintained (otherwise the patient could suffer from low sugar or a potassium-related arrhythmia). Numerous investigatores followed up on this discovery, and determined that a gadolinium demarcated defect less than half the heart wall thickness corresponded clinically to viable myocardium (meaning one could expect improved function after revascularization of a blocked blood supply) whereas a defect more than half the wall thickness corresponded clinically to non-viable myocardium (no expected significant functional gain from revascularizing that region). Subsequently, a third option for assessment of viability was developed: combined PET and MRI.

PET/MRI device produced “high-quality cardiac MR imaging acquisitions,” overcoming any technical issues of having the PET detector within the MRI’s 3-tesla magnet field, Nensa and colleagues concluded.

“No negative side effects from the integrated imaging system design were observed,” they noted.

The researchers were able to show “a close match” between FDG-PET and MRI in assessing myocardial viability and infarct quantification among patients with acute and chronic myocardial infarction.

“These findings demonstrate the feasibility of clinical cardiac MR imaging with an integrated PET/MRI device,” they added. “However, to prove that the integrated design does not interfere with the performance of the device, a systematic intraindividual comparison with a comparable 3-tesla MRI system and identical sequence parameters is still needed.”

Future studies should investigate whether hybrid FDG-PET/MRI of myocardial infarction can provide additional information compared with MRI or PET alone, according to the authors.


Study shows feasibility of cardiac PET/MRI — with caveats

By Wayne Forrest, AuntMinnie.com staff writer
May 9, 2013

Cardiac FDG-PET/MRI is feasible on an integrated whole-body PET/MRI system, but the hybrid modality still must prove it adds clinical relevance to cases of ischemic heart disease, according to a study published online May 7 in Radiology.

The study from University Hospital Essen in Germany found good concordance with the simultaneous acquisition of FDG-PET and MR images regarding both cine and late gadolinium-enhanced imaging in patients with myocardial infarction.

However, despite the simultaneous MRI and PET acquisition, “consolidated cardiac PET/MRI protocols need to be established, as long examination times associated with fasting seem to compromise patient compliance” with the exams, wrote lead author Dr. Felix Nensa, from the department of diagnostic and interventional radiology and neuroradiology, and colleaguesRadiology, May 7, 2013).

Cardiac feasibility study

The purpose of the study was to determine the feasibility of simultaneous acquisition of cardiac images on an integrated 3-tesla PET/MRI system, and to determine if the placement of the PET detector within the MRI’s field of magnet strength would adversely affect clinical results.

The researchers evaluated 20 consecutive patients with ischemic heart disease who were referred for FDG-PET/MRI between May and December 2012. Among the 20 patients, 14 had confirmed acute ST-elevation myocardial infarction within four to 15 days after interventional revascularization, one had suspected non-ST-elevation myocardial infarction, and five had chronic myocardial infarction.

Ten of the 20 patients underwent additional cardiac PET/CT before their PET/MRI scan.

Individuals with contraindications for gadolinium-based contrast agents and general MRI conditions, such as claustrophobia, were excluded from the study. All patients were asked to detail any personal discomfort or side effects that occurred during the PET/MRI exam.

All imaging studies were performed with an integrated whole-body PET/MRI system with 3-tesla field strength (Biograph mMR, Siemens Healthcare) and the PET insert inside the MRI scanner. All MRI sequences were performed with phased-array body surface coils designed for the PET/MRI system.

For late gadolinium-enhanced qualitative imaging, patients received gadobutrol (GadovistBayer HealthCare Pharmaceuticals) based on a dosage of 0.2 mmol/kg of body weight.

FDG-PET/MRI studies were performed after a fasting period of at least six hours, with FDG administered one hour before imaging with a mean of 202 (± 21) MBq. The scans began at a mean of 129 (± 41) minutes after FDG injection and included an electrocardiographically gated cardiac PET scan with one bed position and 3D image reconstruction.

For the FDG-PET/CT scans, an electrocardiographically gated cardiac PET/CT study was performed with a 128-slice CT unit (Biograph mCT, Siemens). PET scans began approximately 70 (± 12) minutes after FDG injection, with a mean of 211 (± 55) MBq.

Image comparisons

To compare the identification and characteristics of the infarcts between the two hybrid modalities, the researchers mapped the left ventricle with a 17-segment model, as recommended by the American Heart Association. Two-point scoring systems were used to assess myocardial tracer uptake, myocardial wall motion, and myocardial late enhancement in each segment.

In addition, the researchers measured the size of a patient’s infarct zone by drawing regions on the late gadolinium-enhanced MR images and PET images, and it was expressed as a percentage of the entire left ventricular myocardium.

Nensa and colleagues were able to complete 19 of 20 cardiac PET/MRI scans. One patient with ST-elevation myocardial infarction did not finish due to claustrophobia. Total PET/MRI scan time without patient preparation and positioning was 53 (± 3) minutes, and all cardiac MR images were rated as diagnostic in quality.

The analysis of FDG-PET and MRI with the 17-segment model found “good concordance” of the left ventricle with both cine imaging and late gadolinium-enhanced imaging in 18 of the 19 patients.

Of the 306 segments evaluated, 97 (32%) were rated as infarcted on PET images, compared with 93 (30%) rated as infarcted on late gadolinium-enhanced images and 90 (29%) on cine images.

Two-chamber views show “stunned myocardium” in a 66-year-old patient with ST-elevation myocardial infarction and acute occlusion of the left anterior descending artery. Cardiac PET/MRI was performed seven days after intervention. Late gadolinium-enhanced image (top left) shows no infarction zone. Fused late gadolinium-enhanced and PET images (top right) show that tracer uptake was reduced in segments 13-15 and 17. T2-weighted MR image (bottom left) shows myocardial edema (arrows) that corresponded well with the area of reduced tracer uptake on the bottom right image. All images courtesy of Radiology.

The size of the infarct zones averaged 22% of the entire left ventricular myocardium on PET images, compared with an average of 20% on late gadolinium-enhanced images.

Among the subgroup of 10 patients with an additional PET/CT scan, no significant difference in myocardial tracer uptake between PET/CT and PET/MR images was found.

In patient exit interviews, 16 patients cited long examination times (including patient preparation) as a source of discomfort. In addition, 11 patients cited the PET/MRI exam itself, i.e., noise, narrowness, and immobility, while 15 patients did not like having to fast.

Final conclusions

In summary, the PET/MRI device produced “high-quality cardiac MR imaging acquisitions,” overcoming any technical issues of having the PET detector within the MRI’s 3-tesla magnet field, Nensa and colleagues concluded.

“No negative side effects from the integrated imaging system design were observed,” they noted.

The researchers were able to show “a close match” between FDG-PET and MRI in assessing myocardial viability and infarct quantification among patients with acute and chronic myocardial infarction.

“These findings demonstrate the feasibility of clinical cardiac MR imaging with an integrated PET/MRI device,” they added. “However, to prove that the integrated design does not interfere with the performance of the device, a systematic intraindividual comparison with a comparable 3-tesla MRI system and identical sequence parameters is still needed.”

Future studies should investigate whether hybrid FDG-PET/MRI of myocardial infarction can provide additional information compared with MRI or PET alone, according to the authors.

Related Reading

MRI motion correction improves PET/MR image quality, July 6, 2012

SNM: PET/MRI for myocardial perfusion feasible but challenging, June 11, 2012

SNM: Hybrid PET/MRI study among top 5 research papers, June 7, 2011

Copyright © 2013 AuntMinnie.com



SNM: Hybrid PET/MRI study among top 5 research papers

By Wayne Forrest, AuntMinnie.com staff writer

June 7, 2011 — SAN ANTONIO – The first-ever study on the clinical use of PET/MRI and a breakthrough on the use of FDG-PET to detect fevers of unknown origin were among the top research papers outlined Monday at this week’s Society of Nuclear Medicine (SNM) annual meeting.

More than 1,000 papers were submitted for consideration and presentation at this year’s meeting, with many studies showing how molecular imaging is gaining influence in the early detection of Alzheimer’s disease. Other submissions included a first-of-its-kind study on the use of near-infrared fluorescence and a new synthesized imaging agent to discover hidden blood clots in veins and arteries.

Hybrid PET/MRI

Early results from the clinical use of PET/MRI indicate that the hybrid modality can provide important diagnostic information about soft tissues and physiological functions throughout a patient’s body. The technology’s ability to find suspicious lesions and potential cancer already appears comparable to that of conventional molecular imaging methods.

In a German study, 11 patients with cancer underwent single-injection PET/CT followed by PET/MRI (Biograph mMR, Siemens Healthcare). Simultaneous PET/MRI acquisition was feasible and offered good-quality PET and MRI diagnostic data.

The analysis found that all 13 lesions detected at PET/CT were also identified by PET/MRI, with no significant difference between PET/CT and PET/MRI regarding the uptake ratios.

The study “demonstrates for the first time that newly introduced integrated whole-body MR/PET technology allows simultaneous acquisition of high-quality MR and PET data in a clinical setting within an acceptable time frame,” wrote lead study author Dr. Alexander Drzezga from TU München.

The hybrid technology could result in the development of new imaging agents that combine the diagnostic prowess of PET and MRI, Drzezga said. With the ability to image physiologic and pathophysiologic processes at the same time, the technology could open a new imaging discipline within nuclear medicine.

Carcinoma is compared in a patient who received a PET/CT scan 80 minutes after contrast injection (above), followed by a PET/MRI scan 160 minutes after contrast injection (below). All images courtesy of SNM.

FDG-PET and fever of unknown origin

Japanese researchers broke new ground in their study, which concluded that FDG-PET provided additional diagnostic information in cases of fever of unknown origin. The use of FDG-PET also had a high clinical impact, especially among patients with infectious diseases.

The retrospective study evaluated 81 consecutive patients with fever of unknown origin. They underwent FDG-PET at six Japanese institutions between July 2006 and December 2007.

Results were divided into four groups for final diagnoses: infection, arthritis/vasculitis/autoimmune/collagen disease, tumor/granuloma, and other/unknown.

The analysis found that sensitivity was highest in the tumor/granuloma group at 100% (seven of seven cases), followed by infection at 89% (24 of 27 cases) and arthritis/vasculitis/autoimmune/collagen disease at 65% (11 of 17 cases). Sensitivity was 0% (zero of one case) in the other/unknown category. Overall sensitivity was 81% and overall specificity was 75%.

Additional information provided by FDG-PET was highest in the infection group, at 76% of the cases (22 of 29), followed by tumor/granuloma at 75% (six of eight), arthritis/vasculitis/autoimmune/collagen disease at 43% (nine of 21), and other/unknown at 23% (five of 22).

The other/unknown group showed a high specificity of 84% (16 of 19 cases) and accurately excluded active focal inflammatory diseases and malignancy.

Lead study author Dr. Kozuo Kubota, PhD, chief of nuclear medicine at the National Center for Global Health and Medicine in Tokyo, said that until now, conventional modalities have produced low imaging resolution and very poor detectability for the fever’s cause.

“If the CT scan, ultrasound, or other conventional imaging technique fails, it is very difficult to find ways to find the focus of the fever,” Kubota said. “If we use FDG-PET, we can scan from head to thigh in only one scan to detect where the truly active lesion is. FDG is very sensitive both for inflammation and the tumor.”

With the addition of FDG-PET, physicians discovered a graft infection in a 50-year-old male with kidney failure and fever of unknown origin, with high FDG uptake illustrating the malady.

“I view this [study] as extraordinary,” said Dr. Michael Graham, PhD, director of nuclear medicine at the University of Iowa, who announced the top five papers. “This is in a setting where modern medicine is unable to come up with the answer, even after weeks. In about an hour-and-a-half, an FDG-PET scan came up with the answer with excellent sensitivity. We don’t get it every single time, but if it weren’t done, it would be mysterious what the patient had. It would be treated with antibiotics and hope for the best.”

“This is a huge step forward and I think it will change how we approach this problem,” he said.

PET and Alzheimer’s detection

Three studies presented at SNM 2011 added to the growing evidence that PET is an effective method to detect Alzheimer’s disease in its early stages, and that it provides a pathway to future clinical screening and treatments.

One lead study author, Dr. Kevin Ong, research scientist at Austin Hospital in Heidelberg, Australia, said that amyloid imaging with PET scans can help ascertain the likelihood that individuals will deteriorate cognitively within a few years, enabling more efficient channeling of healthcare resources.

Molecular imaging of Alzheimer’s disease has focused on detecting and analyzing the formation of the protein beta amyloid in the brain, which researchers say is directly involved in the pathology of Alzheimer’s. The presence of significant amyloid buildup is also linked to more rapid memory decline and brain atrophy.

Increased amyloid is bad for cognition even in the healthy elderly, noted lead study author Michael Devous Sr., PhD, director of neuroimaging for the Alzheimer’s Disease Center at the University of Texas Southwestern Medical Center.

The three ongoing studies involve several years of research based on hundreds of participants ranging widely in age, cognitive ability, and stage of disease.

Collective results showed that amyloid plaques build up at an estimated rate of 2% to 3% per year, and they often are already present in healthy older individuals. Amyloid plaque was present in 12% of people in their 60s, 30% of those in their 70s, and 55% of those older than 80.

In one study, approximately 25% of subjects older than 60 had amyloid plaques.

For individuals who have already developed a measurable memory decline, a positive scan for amyloid is the most accurate predictor of progression to Alzheimer’s disease, said Dr. Christopher Rowe, a lead investigator for the Australian Imaging, Biomarkers, and Lifestyle study of aging and professor of nuclear medicine at Austin Hospital.

Amyloid imaging with PET scans, he added, will be an important new tool in the assessment of cognitive decline.

Several studies have used carbon-11-labeled Pittsburgh Compound B (C-11 PIB), a PET imaging agent that binds to beta amyloid in brain tissue, but two of the current studies are assessing the benefit of F-18 florbetaben and F-18 florbetapir, which are designed for routine clinical use.

Both F-18 florbetaben and F-18 florbetapir are showing promise as reliable predictors of progression to Alzheimer’s disease, and F-18 amyloid imaging agents are considered most likely to move into clinical practice in the near future, perhaps as soon as next year.

NIRF for blood clot detection

In another novel study at SNM 2011, researchers from Massachusetts General Hospital are using near-infrared fluorescence (NIRF) and a new synthesized imaging agent to detect blood clots inside elusive veins, often within the deep tissues of the thighs and pelvis.

The agent uses a biomarker that seeks out a peptide — called fibrin — that is actively involved in the formation of blood clots. Combined with NIRF, which uses light energy to gather information from cells and tissues, the technique could also be used for coronary arteries. The fibrin peptide agent (EP-2104R) has already been tested in phase II clinical trials.

Lead study author Dr. Tetsuya Hara, PhD, noted that the availability of a high-resolution fibrin sensor is important for two reasons: intravascular NIRF imaging of coronary-sized arteries is now possible, and coupling the fibrin peptide with this technique may allow researchers to study coronary artery plaques and stents, which could potentially help identify patients at increased risk of heart attack.

The researchers were able to successfully detect fibrin-rich deep vein thrombosis with both intravital fluorescence microscopy and noninvasive fluorescence molecular tomography, allowing information to be acquired about tissues by analyzing how light is absorbed and scattered.

By coupling the fibrin peptide agent with intravascular NIRF imaging, researchers can now study microthrombi on coronary artery plaques and coronary stents that are at high risk for thrombosis and vessel occlusion.

This advance could help clinicians predict potential heart attacks and other major cardiovascular events, potentially saving more patients’ lives.

Related Reading

SNM exceeds fundraising goal, June 6, 2011

SNM: PET/MRI must prove its worth to ensure clinical adoption, June 6, 2011

PET/CT with NaF bone agent takes SNM’s Image of the Year, June 6, 2011

SNM proposes name change, May 3, 2011

SNM’s Clinical Trials Network: Progress despite growing pains, April 29, 2011



Copyright © 2011 AuntMinnie.com

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