(5) Cardiovascular Imaging Group
Carotid Atherosclerotic Plaque Imaging
The Cardiovascular Imaging Group is also working on carotid atherosclerotic plaque imaging using 3 Tesla MRI. Arterial plaque contains unstable plaque and stable plaque. It has been reported that unstable plaque sometimes has large lipid core and thin fibrous cap, intraplague hemorrhage, or has plaque inflammation. With MRI, a variety of contrasts can be applied to soft tissues by change the imaging parameters, which makes it possible to evaluate the composition of the plaque. Using this technology to visualize the plaque shows promise of being useful in preventing, prognosticating, and determining treatment measures for cardiovascular disease.
Fig. 1 Plaque with a lipid core (yellow arrow)
Fig. 2 Unstable plaque with intraplague hemorrhage (white arrow)
( Text by Minako Oikawa )
Role of Cardiac MRI
Cardiac MRI is non-invasive, very useful for functional and tissue characterization diagnosis, and play a major role in cardiovascular treatment. The Department makes active use of Cardiac MRI in the diagnosis of disease including ischemic heart disease, cardiac sarcoidosis, cardiomyopathy, and congenital cardiac disease. With heart MRI a variety of imaging methods are combined to perform functional, morphological, and tissue characterization assessments.
1.Cine MRI
Diagnosis of left ventricle wall motion and left ventricle pump function using cine MRI is thought to be the most accurate cardiac function evaluation in terms of reproducibility and sensitivity compared to other imaging methods (Figure 1). In addition, the excellent spatial resolution and application to select the tomographic view makes MRI useful in understanding the anatomy of the cardiac atrium, cardiac ventricle especially, in complex cardiac abnormalities. Useful information for the diagnosis of cardiac tumor and cardiac thrombus can also be obtained by combining T1 weighted images, T2 weight images, and cine MRI. 
Fig. 1 Left ventricle cine MRI image
Cine MRI obtains excellent spatial resolution and for the diagnosis of left ventricle wall motion and left ventricle pump function it is thought to be the most accurate cardiac function evaluation method in terms of reproducibility and precision compared to other imaging examination methods.
2.Stress Myocardial Perfusion MRI
In Japan, nuclear examinations seems to be the primary method for evaluating myocardial ischemia. The Department uses stress myocardial perfusion MRI in addition to nuclear examinations for diagnosis and evaluation of ischemic heart disease. Myocardial perfusion MRI can be used to evaluate the ischemic area by using dynamic MRI to monitor the myocardial first pass dynamic after bolus administration of MRI contrast medium while conducting pharmacological stress. Because subendocardial ischemia can be evaluated, the diagnostic performance is considered to be as good as or rather better than stress myocardial perfusion SPECT (Figure 2).
Fig. 2 Stress perfusion MRI before and after percutaneous coronary intervention (PCI)
Pre-PCI pharmacological stress causes the is chemic area shown by the white arrow to demonstrate a low signal. The ischemia is improving after PCI. A part of the low-signal area after stressing also have a high signal using delayed enhancement(with black arrow) and was diagnosed to be infarction.
3.Delayed-Enhancement MRI
Delayed-enhancement MRI that uses a gadolinium (Gd) contrast medium can clearly show the myocardial infarction area and is also useful for diagnosing subendocardial infarction and evaluating myocardial viability (Figure 1) and sarcoidosis(Figure 3), which are difficult to capture using SPECT. The Gd contrast medium is distributed within the blood vessels and the extracellular fluid and has the property of not distributing normal cells. Delayed-enhancement MRI is a method that captures a T1 weighted image approximately 15 min after contrast medium administration to detect infarction areas. In infarction areas the myocardial cell component is decreased and the extracellular fluid component is relatively increased, thus giving a high signal when using delayed-enhanced MRI.
Fig. 3 Delayed-enhanced MRI and PET of cardiac sarcoidosis
The area exhibiting the high MRI signal matches with a high accumulation by PET.
( Text by Koichiro Sugimura )
Nuclear Cardiology (SPECT, PET)
The Department is cooperating with the Department of Diagnostic Radiology and the Institute of Development, Aging and Cancer. Nuclear cardiology uses a variety of tracers to non-invasively study cardiac blood flow, ischemia, metabolism, inflammation, autonomic nerve function, and other items. In addition to the conventional myocardial SPECT (Single Photon Emission Computed Tomography), cardiac PET (Positron Emission Tomography) is also possible, and studies are being conducted to see if FDG-PET is useful for diagnosis of myocardial ischemia and diagnosis of inflammatory diseases such as cardiac sarcoidosis. In combination with other diagnostic imaging methods, is also useful for nuclear imaging identifying the pathology of cardiac diseases (Figure 4).
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Figure 4: A perfusion defect is seen in this 99mTc-MIBI perfusion scintigraphy in the left ventricle lateral wall area that matches the MRI delayed enhancement (Left: white arrow area). |
For clinical research gated myocardial perfusion SPECT (QGS method) is used to evaluate the effect of cardiac resynchronization therapy (CRT) using biventricular pacing for severe cardiac failure patients (Figure 5). In addition, in cooperation with the Aobayama Radioisotope Center, PET is being used to study pulmonary hypertension and the myocardial metabolism of cardiomyopathy.
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Fig.5: Improvement in wall motion for was found after CRT in left ventricular endomyocardial wall motion images obtained with 99mTc-MIBI myocardial perfusion scintigraphy. |
Echocardiography
The Department has exclusive use of the latest wish–end echocardiography equipment ,as well as the portable echocardiography. In addition, routine echocardiography examinations of outpatients are supervised by a full-time sonographer. In addition to regular echocardiography examinations, special echocardiography examinations, such as transesophageal echocardiography, are actively performed. It is also useful for severe patients arrving at the emergency room to make the diagnosis.
For clinical research, the efficacy of biventricular pacing is being studied using the tissue Doppler method (Figure 6) .
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Fig. 6: Synchronous left ventricle wall motion of the CRT is shown by M-mode echocardiography and tissue doppler. |
( Text by Yuji Wakayama )