The following factors should be checked before interpreting images to evaluate the diagnostic quality of images.
- Presence of contrast in the images: If a sufficient amount of contrast material has been administered, liver and kidney in the imaging plane should be enhanced (). All structures will appear too dark if contrast has extravasated or washed out.
Figure 2 Normal post-contrast segmented inversion recovery spoiled gradient echo delayed enhancement image in a 38-year-old male. Increased signal intensity in liver (white arrow) and kidney (black outlined notched arrow) confirm presence of gadolinium-based contrast (more ...)
- Inversion time adjustment: If inversion time is appropriate, normal myocardium should appear hypointense, the blood pool signal should be of intermediate intensity and myocardial scar should be the most intense structure in the image ().
Figure 3 Appropriate suppression of myocardial signal by inversion time adjustment in a 56-year-old male with myocardial infarction. Myocardial signal was suppressed successfully using an appropriate inversion time and myocardium was seen as hypointense in the (more ...)
The fibrous skeleton of the heart (e.g. mitral valve annulus) is often hyperintense because of gadolinium accumulation in these highly collagenous areas. Heart valves also faintly enhance ().
Figure 4 Normal enhancement of valves and their annuli in a 54-year-old male. Four-chamber segmented inversion recovery spoiled gradient echo image shows contrast enhancement in mitral and tricuspid valves (arrowheads) and their annuli due to accumulation of contrast (more ...)
If the inversion time is slightly shorter than optimal inversion time, normal myocardium appears grey in between hypointense endo- and epicardial lines ().
Figure 5 Unsuccessful suppression of myocardial signal due to suboptimal inversion time adjustment in a 45-year-old male with a history of myocardial infarction. Segmented inversion recovery spoiled gradient echo magnitude image (a) in the short-axis plane demonstrates (more ...)
If very long inversion time is used, the image contrast is reduced. Images acquired with suboptimal inversion time may lead to inaccurate assessment of scar size [6
]. An IR-SSFP look-locker sequence is used to select the optimal inversion time visually for maximising the signal intensity between normal and scarred myocardium [7
Figure 6 Selection of optimal inversion time in a patient with a history of myocardial infarction. One short-axis slice of the left ventricle at the level of inferior papillary muscle insertion point is repeatedly obtained using different inversion times varying (more ...)
Since each slice can be obtained in one breath-hold with the IR-GRE sequence, the TI time should be slightly lengthened as the delay after contrast increases. Another way to achieve a consistent contrast over a wide range of inversion times is to apply phase-sensitive reconstruction. This method uses phase information to correct magnitude images when TI times are incorrectly determined [8
] (). The phase-sensitive reconstruction method also reduces the variation in apparent infarct size. In patients with breath-holding difficulty, DE-CMR can be performed using a nominal inversion time value in combination with IR-SSFP sequence which will obviate the need for extra breath-hold for the look-locker sequence to optimise inversion time. A disadvantage of phase-sensitive inversion recovery images is that noise may be more prominent in the image.
We interpret a hyperintense region as definite when it is confirmed either in two adjacent short-axis images or in one short-axis image and a long-axis image at a corresponding location. Confirmation of scar in two different images avoids misinterpretation of artefacts or image features that may be due to motion artefacts, morphological variations or septal clefts. However, very small focal myocardial scar areas might be missed since slice thickness is 6–8 mm.