This talk will be presenting recent advances in late gadolinium enhancement (LGE) cardiac imaging which can overcome limitations of the standard protocol based on inversion recovery segmented 2D acquisition. The advanced approaches to be discussed will include single-shot imaging with motion corrected averaging, single-breath-hold 3D imaging, free-breathing isotropic 3D imaging with respiratory, and techniques to improve scar-blood contrast and scar-fat contrast.
Single shot imaging: Compared to the segmented acquisition, single-shot imaging is faster and less sensitive to respiratory motion and arrhythmia at the cost of reduced spatial resolution. Single shot LGE may be used for covering the entire myocardium in a single breath-hold (1) or in cases of arrhythmia or poor breath-holding(2). Motion corrected averaging can be used for free-breathing scans to further reduce motion effect and enhance SNR(3).
Breath-hold 3D imaging: 3D LGE has advantages of contiguous 3D coverage which guarantees accurate quantification of scar volume, shorter total scan time due to the lack of rest periods, and higher SNR which can be traded for higher spatial resolution. While 3D LGE typically enables lower spatial resolution or longer scan time then the conventional 2D approach, non-Cartesian acquisition may be used for scan acceleration(4-7).
Free-breathing isotropic 3D imaging: Isotropic resolution 3D LGE is arguably the most desired but would be feasibly only through free-breathing scan due to excessively long scan time. The most important of technical requirements in free-breathing LGE is accurate motion estimation and compensation. Diaphragm navigator is the most established approach but with limited accuracy due to subject-dependent motion correlation between the diaphragm and heart. More accurate motion estimation directly using the signal from the heart (i.e. self-navigation) has been investigated in multiple cardiac applications (8-10). Scan acceleration is another important requirement in isotropic LGE to maintain acceptable scan time. With parallel imaging reconstruction is the default method, addition of compressed sensing appears to be promising for high-rate scan acceleration (11,12) .
Enhancing scar-blood contrast: Image contrast between subendocardial MI and nearby blood pool is often low because of similar T1 values, which makes it difficult to outline the scar boundary accurately. A useful basis for differentiation between scar and blood is difference in their T2 values. This can be utilized simply by additionally acquiring T2 weighted images at the cost of increased scan time(13). The same concept evolved into black blood LGE where an inversion recovery T2 preparation pulse well contrasts scar with blood as well as remote myocardium (14).
Distinguishing fat from scar: Intramyocardial fat may be of diagnostic value but is difficult to distinguish from MI since both have low T1 values. Fat-only images can be obtained by using multiecho readout and an iterative estimation algorithm which simultaneously solves for water, fat, and field offset (15,16).
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