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Imaging
Figure 1: Magnetic Resonance Figure 2: Long-axis Two-
Conclusion
Perfusion Imaging chamber View Showing a
In patients with moderate or worse ECG image quality, DSMR can be
Transmural Necrosis
regarded as the imaging method of choice. It can prove or exclude ischemia
Aligned with strong prognostic value. In addition, low-dose DSMR yields a
functional answer on the presence of viable (hibernating) myocardium.
P
Perfusion
The first multicenter trials have shown promising results for MR first-pass
perfusion imaging
15,16
for the detection of ischemia. A major advantage of
MR perfusion imaging in comparison with other perfusion imaging
techniques, e.g. single photon emission computed tomography (SPECT) or
FFE/M
SI 2
H positron emission tomography (PET), is its ability to visualize subendocardial
L
Ph 1/365 ms A P
Dy 26/19.6 s
perfusion defects due to its superior spatial resolution. PET and SPECT have
F
F
additional limitations compared with MR perfusion, such as the application
Figure 1: Equatorial short-axis view during adenosine stress. There is a stress-induced perfusion
of radioactive tracers and the occurrence of attenuation artifacts for SPECT.
defect in the anterior and anteroseptal segment (white arrows).
Figure 2: A transmural necrosis (late gadolinium enhancement pattern) in the mid-inferior
segment in the right coronary artery territory (white arrows).
Stress Agents
For MR perfusion imaging, pharmacological vasodilatation is induced with
Diagnostic Criteria adenosine or dipyridamole. Adenosine stimulation causes an increase of
A synchronized display of the different dobutamine dose levels at the same blood flow in myocardial areas supplied by normal coronary arteries,
time is used for a standardized assessment of wall motion abnormalities. Wall whereas no change or even a reduction is found in areas supplied by
motion is classified as normokinetic, hypokinetic, akinetic, or dyskinetic. During stenotic coronary arteries. With an intravenous infusion of 140µcg/
DSMR, a lack of increase in wall motion or systolic wall thickening or a kg/minute adenosine for four to six minutes, maximal coronary vasodilation
reduction of wall motion or thickening are regarded as pathological findings. can be safely achieved. Possible side effects—such as first-, second-, and
DSMR has been shown to be superior to DS ECG for the detection of inducible third-degree atrioventricular (AV) block, sinus bradycardia, and dyspnea—
wall motion abnormalities in patients with suspected coronary artery disease,
7
are transient and usually do not require medical intervention.
patients with wall motion abnormalities at rest,
8
and patients not well suited
for second harmonic echocardiography.
9
The superiority of DSMR has been Contrast Agents and Injection Scheme
primarily attributed to the consistently high endocardial border visualization. In MR perfusion imaging is performed during a rapid bolus injection of a low
patients with inadequate acoustic windows or limited ECG image quality, the dose of standard gadolinium-containing extracellular contrast agent.
advantage in diagnostic accuracy is particularly high. A recently published Usually, contrast agent doses between 0.05 and 0.15mmol/kg with injection
multicenter study showed that DSMR has low inter-observer variability.
10
In a speeds of 3–6ml/kg are used. First-pass myocardial perfusion imaging is
recent review, a meta-analysis of DSMR for identifying coronary atherosclerosis completed within 30–50 seconds immediately after the contrast agent
demonstrated a sensitivity of 87% with a specificity of 83%.
11
administration and is normally performed during a breath hold. The whole
examination consists of cine wall motion imaging at rest, followed by
Functional Assessment of Viable Myocardium perfusion imaging at stress (adenosine), then 10 minutes later at rest, and
In addition to the assessment of ischemia, DSMR offers the possibility of finally delayed enhancement imaging (DE) as described below.
17
detecting viable myocardium after myocardial infarction (MI). This information
is based on the recruitment of hibernating myocardium with doses of Analysis of Magnetic Resonance Perfusion Studies
10–20µg/kg/minute dobutamine stimulation. In areas with viable myocardium A visual analysis of the data is performed in most centers. A semiquantitative
a ‘biphasic response’ is observed, characterized by wall motion abnormality at evaluation of MR perfusion imaging is recommended for a more accurate
rest, improvement at low dose, and worsening at higher dobutamine doses. interpretation. In areas with ischemia inflow, the contrast agent will be reduced
Low-dose dobutamine has a similar value to MR scar imaging (late and slower in comparison with normal areas, which leads to a reduction of
enhancement) for the prediction of functional recovery after revascularization signal intensity in ischemic myocardium (see Figure 1). In patients with previous
and may be superior in patients with 25–75% transmurality of necrosis.
12
MI, the dark zones must be larger than or in a different area from the
enhancement to make the diagnosis of ischemia.
18
Recently, a significant
Prognostic Value of Dobutamine Stress Magnetic Resonance number of studies
19–22
have underlined the accuracy of MR perfusion imaging,
In a single-center study, Hundley et al.
13
found that the presence of inducible which is a least as accurate as SPECT if performed in an experienced center.
wall motion abnormalities during DSMR identifies patients at risk for MI and
cardiac death, independent of the presence of traditional risk factors for Prognostic Value of Magnetic Resonance Perfusion
CAD. For patients with a left ventricular ejection fraction (LVEF) >40%, a Patients with normal stress myocardial perfusion have an excellent prognosis.
low cardiac event rate (2% over two years) was demonstrated. Jahnke et Jahnke et al. demonstrated that a negative perfusion study was related with
al.
14
reported a cumulative cardiac event rate (death or MI) of 1.2, 2.6, and 0.7, 0.7, and 2.3% cumulative cardiac event rates for the first three years,
3.3% in the first three years in patients with a normal DSMR. In contrast, respectively. There was a significantly lower event rate than in patients with
patients with a positive DSMR had a significantly higher event rate (7.3, a positive MR myocardial perfusion study: 6.2, 12.2, and 16.3% in the first
10.3, and 18.8% in the first three years). three years, respectively.
14
In a recent study from Ingkanisorn
23
et al. in
32 US CARDIOLOGY
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