الفهرس 
Perfusion ImagingOnly 14 pages are availabe for public view
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Abstract
A definite distinction between viable and nonviable myocardium in patients with coronary artery
disease and left ventricular dysfunction is important. Several methods, including assessment of
myocardial perfusion and metabolism by positron emission tomography (PET), cellular membrane
integrity by single photon emission computed tomography (SPECT), and improvement of wall motion
and thickening by inotropic stimulation ( with two-dimensional echocardiography, contrast
ventriculography, or magnetic resonance imaging ), have been used to predict viable myocardium (Li
et al., 1996).
During the past decade, myocardial scintigraphy with Thallium -201 has achieved a preeminent
position for its use in the clinical assessment of myocardial viability in patients with coronary
artery disease (Rainer et al., 1995) .
After acute myocardial infarction, myocardial stunning may cause reversible left ventricular
dysfunction as opposed to the irreversible damage caused by necrosis (Carl et al., 1995). Regional
and global left ventricular function may then improve over time or with revascularization. Because
there is an uncoupling between regional myocardial perfusion and contraction, assessment of
ventricular function and vascular patency may be insufficient to assess myocardial viability (Carl
et al., 1995). ·
By use of modified imaging protocols (Hartenstein et al., 1993) , (Civelek et al., 1993), (Kayden
et al., 1991) and (Rocco et al., 1990), it has been shown that Thallium-201 scintigraphy indentifes
quite the same myocardial regions as
viable or nonviable as positron-emission tomography imaging with F
fluorodeoxyglucose (Bonow et al.,1991), the current reference tracer for the assessment of
myocardial viability.
Actually, Thallium-201, a potassium analog is the most widely used and standard perfusion
myocardial agent. It is primarily distributed within the myocardium via regional myocardial blood
flow but requires cell integrity and intact sodium potassium ATP-ase pump activity for
intracellular uptake (Robert and Vasken, 1992). So Thallium-201 scintigraphy is proved to be a
reliable detector of myocardial viability (Christian et al., 1994 ) and ( Marzullo et al., 1993).
New Technetium based agents as Sestamibi, a cationic compound which is distibuted via myocardial
blood flow and traverses cell membrane to concentrate within mitochondrial wall (Udelson et al.,
1994).Myocardial Sestamibi uptake reflects regional flow distribution and cellular integrity
however, some segments showing reduced tracer uptake at rest may consist of viable although
hypoperfused myocardium (Sinusas et al.,1993), (Sawada et al., 1994) and (Douglas, 1995).
It is speculated that the adminstration of nitroglycerin (NTG) before the Sestamibi injection would
improve its uptake in resting hypoperfused regions and provide us with a cheaper reliable detector
of myocardial viability (Galli et al., 1994).
Inevitably, we now need studies of adequate design and size to establish the role of
Technetium-99m Sestamibi in the assessment of myocardial viability in comparison with Thallium-201.
Although the studies done were all comparing both techniques but none was done after enhancement of Sestamibi with
sublingual nitroglycerine. However a rationale and model for the development of new cardiac
imaging agents must emerge (Douglas, 1995).
New radio-tracers must offer patient dosimetry advantages, improved spatial or temporal image
resolution, or provide diagnostic information on a previously unmeasurable but clinically relevant
biological parameter.