Color-map recommendation for MR relaxometry maps

Abstract

Purpose: To harmonize the use of color for MR relaxometry maps and therefore recommend the use of specific color-maps for representing $T_1$ , $T_2$ , and $T_2^{*}$ maps and their inverses.

Methods: Perceptually linearized color-maps were chosen to have similar color settings as those proposed by Griswold et al. in 2018. A Delphi process, polling the opinion of a panel of 81 experts, was used to generate consensus on the suitability of these maps.

Results: Consensus was reached on the suitability of the logarithm-processed Lipari color-map for $T_1$ and the logarithm-processed Navia color-map for $T_2$ and $T_2^{*}$ . There was consensus on color bars being mandatory and on the use of a specific value indicating "invalidity." There was no consensus on whether the ranges should be fixed per anatomy.

Conclusion: The authors recommend the use of the logarithm-processed Lipari color-map for displaying quantitative $T_1$ maps and $R_1$ maps; likewise, the authors recommend the logarithm-processed Navia color-map for displaying $T_2$ , $T_2^{*}$ , $R_2$ , and $R_2^{*}$ maps. This work originated with the Quantitative MR Study Group of the International Society of Magnetic Resonance in Medicine (ISMRM); it has the approval of the Publication Committee and of the Board of the ISMRM.

Keywords: color; display; quantitative MR; relaxation; standardization.

FIGURE 1

(A1,A2) Maps of the myocardium of 2 different patients; healthy tissue (A2) may be depicted as purplish, whereas an orange‐like color points to pathology (A1; white arrow). (B1) Example of a brain T₁ map. (B2) Example of a brain T₂ map. (C1) Example of an image providing a T₂ map of a knee (see C2 for detail); it contains a T₂ map of cartilage (in color) as well as the context of “weighted” anatomy information (in gray).

FIGURE 2

Images shown in Rounds 1 and 3 of the Delphi process. (A) Example of Griswold 2018 color‐maps (copied from ref. 31). (B) Initial version of the Lipari map. (C) Initial version of the Navia map. (D) The (visualized) multiple‐choice question of Round 3: “Lipari for ${\mathrm{T}}_1$, Navia for ${\mathrm{T}}_2$”↔ “Lipari for both ${\mathrm{T}}_1$ and ${\mathrm{T}}_2$” ↔ “Gray for both ${\mathrm{T}}_1$ and ${\mathrm{T}}_2$.”

FIGURE 3

Collection of ${\mathrm{T}}_1$ images as presented to the panel during Round 4. See Supporting Information for full‐sized images.

FIGURE 4

Collection of ${\mathrm{T}}_2$ images as presented to the panel during Round 4. See Supporting Information for full‐sized images.

FIGURE 5

From Round 2, the number of respondents by country/region. Each block represents one person. Shades of purple reflect Europe; gray is North America; shades of green refer to Asia; and shades of blue refer to the Middle East. One responder preferred not to state his region, so only 47 responders are shown here.

FIGURE 6

(A,B) The color bar and labeling as used in the questionnaire of Round 4 (A) and as used in the last, limited, questionnaire (B). The images were identical in both cases (e.g., 1500 ms being displayed as orange in both cases). (B) is the recommended choice.

FIGURE 7

Example of a prostate T₁ map (left) and the corresponding R₁ map (right) displayed using the logarithm‐processed inverted Lipari color‐map. Given the logarithm processing, with the inverted map, the R₁ looks almost identical to the T₁ map. Note that the logarithm is not applied to the maps themselves but by processing the color‐map. This is apparent by the difference between the color bars: The color corresponding to the ${\mathrm{T}}_1$ value that is linearly halfway (400 ms and 2000 ms) is much brighter than the color corresponding to the ${\mathrm{R}}_1$ value that is linearly halfway (0.5/s and 2.5/s).

FIGURE 8

The recommended (unprocessed) color‐maps: Lipari (top) and Navia (bottom).