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Page 4 of 11 Pica et al. Vessel Plus 2022;6:10 https://dx.doi.org/10.20517/2574-1209.2021.81

LGE imaging can be challenging in advanced stages with extensive involvement and almost no normal
myocardium. The operator can erroneously null the abnormal myocardium, missing global infiltration or
creating a false subendocardial sparing appearance; the development of phase sensitive inversion recovery
(PSIR) sequences has made LGE imaging more robust and operator independent, overcoming this
limitation .
[22]
Global subendocardial enhancement and transmural LGE are typical features of CA, with a sensitivity of
86% and a specificity of 92% , and increasing LGE extent shows good correlation with the degree of
[23]
myocardial infiltration. LGE presents an initial basal predilection, progressing to biventricular transmurality
in advanced disease, whereas early stages of CA can present with focal or even absent LGE, making the
[24]
diagnosis more challenging [Figure 1]. Finally, LGE is highly prevalent and more extensive in ATTR than
AL, but with similar progression and significant overlap between the subtypes [22,24,25] .

T1 and T2 mapping imaging
T1 mapping is a relatively new technique, where a direct quantitative signal from the myocardium is
measured. Each pixel in the image is coded in color, reflecting the absolute T1 values in milliseconds. Pre-
contrast T1 measures intrinsic signal from the myocardium due to its composition (native myocardial T1).
Pathological processes changes T1, with reduced values in iron or fat infiltration, such as Fabry disease.
Native T1 increases modestly in diffuse fibrosis, more in scar, and substantially in amyloid, being as high as
5 SD or higher than normal, often allowing a differential diagnosis vs. other hypertrophic phenotypes [21,26,27]
[Figure 2].

Native T1 presents high diagnostic accuracy for CA in both AL and ATTR with high pre-test probability,
and it has been validated as a surrogate marker of infiltration, with good correlation with disease severity
and markers of systolic and diastolic dysfunction [28,29] . Furthermore, native T1 demonstrated high accuracy
in patients with suspected CA with various degrees of kidney dysfunction, showing very high positive and
[30]
negative predictive values for extremely high and low T1 values, respectively .

In patients with eGFR < 30 mL/min/1.73 m , it is generally suggested to avoid contrast administration,
2
although currently used macrocyclic agents show a very good safety profile; in this setting, an individual
assessment of the risk-to-benefit ratio should be considered, taking into account that CA could be detected
by native T1 in a proportion of patients with advanced renal failure avoiding contrast, as well as reducing
costs and time . However, native T1 showed limited accuracy in patients with intermediate values.
[30]
Furthermore, native T1 is a composite signal from both the extra- and intracellular space and cannot fully
[30]
differentiate the underlying processes, particularly edema and amyloid .
After gadolinium administration, using the ratio of pre- to post-contrast T1 and hematocrit, the signal from
the extracellular space can be isolated with the calculation of the extracellular volume (ECV), representing
purely the extracellular expansion, which is the closest quantifier of amyloid burden within the heart.

Amyloidosis is the exemplar interstitial disease, and this is reflected by massive ECV elevation, up to 0.50-
0.60 in definite CA. While ECV in healthy subjects is 0.22-0.28, it increases hugely in focal scar or edema,
but, for diffuse fibrosis (aortic stenosis and hypertensive heart disease), the increases are 0.30-0.35.

A global ECV increase around 0.40 should raise the suspicion of CA. In fact, ECV showed a tight
incremental correlation with probability of cardiac involvement based on echocardiographic and bio-
[31]
humoral findings in AL , and it agreed well with ECV measured by histology, representing a direct marker