Liver Tissue Characterization in Competitive Student Athletes by Quantitative MRI: Normal Values

Statistical analysis

A placeholder for description of statistical methods.

Patient characteristics

Summary statistics for patient demographics and mean values of PDFF, R2*, T1, T2, and LIC are provided by sex and field strength in Table 1 and Table 2, respectively.

Table 1:
Subject characteristics and measurements by sex.
Characteristic	Female, N = 49¹	Male, N = 89¹	Overall, N = 138¹	p-value²
Age (years)	19.0 (18.6, 20.0)	19.0 (19.0, 21.0)	19.0 (18.9, 20.9)	0.13
AthleteType
Basketball	2 (4.1%)	0 (0%)	2 (1.4%)
Cross country	0 (0%)	2 (2.2%)	2 (1.4%)
Diver	1 (2.0%)	0 (0%)	1 (0.7%)
Football	0 (0%)	50 (56%)	50 (36%)
Hockey	1 (2.0%)	0 (0%)	1 (0.7%)
Ice Hockey	9 (18%)	8 (9.0%)	17 (12%)
Rower	15 (31%)	8 (9.0%)	23 (17%)
Soccer	4 (8.2%)	4 (4.5%)	8 (5.8%)
Softball	5 (10%)	0 (0%)	5 (3.6%)
Swimmer	0 (0%)	1 (1.1%)	1 (0.7%)
Tennis	1 (2.0%)	1 (1.1%)	2 (1.4%)
Track athlete	6 (12%)	9 (10%)	15 (11%)
Volleyball	5 (10%)	0 (0%)	5 (3.6%)
Wrestler	0 (0%)	6 (6.7%)	6 (4.3%)
Height (cm)	172.7 (165.0, 178.3)	188.0 (183.0, 193.0)	183.0 (175.0, 189.0)	<0.001
Weight (kg)	71.0 (65.8, 77.0)	93.0 (81.2, 109.0)	82.0 (71.1, 102.8)	<0.001
BMI	23.8 (22.1, 25.1)	26.6 (24.2, 30.8)	25.3 (22.9, 28.8)	<0.001
Field strength				0.4
1.5T	23 (47%)	49 (55%)	72 (52%)
3T	26 (53%)	40 (45%)	66 (48%)
PDFF	1.8 (1.6, 2.3)	2.1 (1.8, 2.8)	2.0 (1.7, 2.6)	0.027
R2s	36.0 (32.2, 41.5)	37.7 (32.7, 44.0)	36.8 (32.6, 43.2)	0.2
T1	667.3 (593.5, 753.1)	583.9 (544.3, 644.4)	602.6 (557.5, 693.7)	<0.001
T2	49.8 (45.2, 53.1)	46.6 (44.0, 50.5)	47.1 (44.3, 51.2)	0.021
LIC	0.590 (0.512, 0.678)	0.644 (0.572, 0.730)	0.633 (0.554, 0.718)	0.007
¹ Median (IQR); n (%)
² Wilcoxon rank sum test; Pearson’s Chi-squared test

Table 2:
Subject characteristics and measurements by field strength.
Characteristic	1.5T, N = 72¹	3T, N = 66¹	Overall, N = 138¹	p-value²
Sex				0.4
Female	23 (32%)	26 (39%)	49 (36%)
Male	49 (68%)	40 (61%)	89 (64%)
Age (years)	19.0 (18.9, 20.8)	19.0 (18.9, 20.9)	19.0 (18.9, 20.9)	0.7
AthleteType				0.017
Basketball	1 (1.4%)	1 (1.5%)	2 (1.4%)
Cross country	1 (1.4%)	1 (1.5%)	2 (1.4%)
Diver	0 (0%)	1 (1.5%)	1 (0.7%)
Football	35 (49%)	15 (23%)	50 (36%)
Hockey	1 (1.4%)	0 (0%)	1 (0.7%)
Ice Hockey	8 (11%)	9 (14%)	17 (12%)
Rower	13 (18%)	10 (15%)	23 (17%)
Soccer	3 (4.2%)	5 (7.6%)	8 (5.8%)
Softball	2 (2.8%)	3 (4.5%)	5 (3.6%)
Swimmer	0 (0%)	1 (1.5%)	1 (0.7%)
Tennis	2 (2.8%)	0 (0%)	2 (1.4%)
Track athlete	3 (4.2%)	12 (18%)	15 (11%)
Volleyball	2 (2.8%)	3 (4.5%)	5 (3.6%)
Wrestler	1 (1.4%)	5 (7.6%)	6 (4.3%)
Height (cm)	188.0 (178.2, 195.2)	180.0 (172.2, 185.0)	183.0 (175.0, 189.0)	<0.001
Weight (kg)	92.5 (73.7, 110.0)	78.1 (68.4, 86.1)	82.0 (71.1, 102.8)	<0.001
BMI	26.5 (23.7, 30.9)	24.3 (22.5, 26.6)	25.3 (22.9, 28.8)	<0.001
PDFF	2.3 (1.9, 2.8)	1.7 (1.5, 2.2)	2.0 (1.7, 2.6)	<0.001
R2s	32.7 (30.8, 35.5)	43.2 (40.8, 47.4)	36.8 (32.6, 43.2)	<0.001
T1	585.6 (557.4, 615.2)	695.7 (576.4, 749.2)	602.6 (557.5, 693.7)	<0.001
T2	47.3 (44.6, 50.4)	46.5 (44.0, 52.8)	47.1 (44.3, 51.2)	0.9
LIC	0.692 (0.642, 0.764)	0.552 (0.521, 0.610)	0.633 (0.554, 0.718)	<0.001
¹ n (%); Median (IQR)
² Pearson’s Chi-squared test; Wilcoxon rank sum test; Fisher’s exact test

BMI

Table 3:
Comparison of BMT by field strength within each sex.
Characteristic	Female			Male
Characteristic	1.5T, N = 23¹	3T, N = 26¹	p-value²	1.5T, N = 49¹	3T, N = 40¹	p-value²
BMI	23.19 (22.01, 25.20)	23.84 (22.49, 24.89)	0.9	29.3 (25.7, 33.7)	25.1 (22.7, 27.1)	<0.001
¹ Median (IQR)
² Wilcoxon rank sum exact test

Comparison of markers by gender and field strength

Normal values (Mean \(\pm\) 2SD) of PDFF, R2*, T1, T2, and LIC are summarized overall and by sex and field strength in Table 4 and shown graphically in Figure 1.

Table 4:
Normal values by sex and field strength.
	Female			Male			Overall
	1.5T, N = 23¹	3T, N = 26¹	Overall, N = 49¹	1.5T, N = 49¹	3T, N = 40¹	Overall, N = 89¹	1.5T, N = 72¹	3T, N = 66¹	Overall, N = 138¹
PDFF	2.5 [0.2, 4.8]	2.2 [-2.0, 6.4]	2.4 [-1.1, 5.8]	3.2 [-1.5, 7.9]	2.2 [-0.1, 4.4]	2.7 [-1.2, 6.6]	3.0 [-1.2, 7.1]	2.2 [-0.9, 5.3]	2.6 [-1.2, 6.3]
R2s	32 [25, 39]	43 [26, 60]	38 [20, 55]	36 [6, 66]	46 [31, 62]	41 [14, 67]	35 [9, 60]	45 [29, 61]	40 [16, 63]
T1	604 [505, 703]	769 [590, 947]	691 [471, 912]	578 [482, 674]	615 [417, 814]	595 [440, 749]	586 [487, 686]	676 [434, 918]	629 [427, 831]
T2	50.5 [41.4, 59.6]	48.2 [34.9, 61.4]	49.3 [37.7, 60.9]	46.2 [38.3, 54.2]	48.2 [33.0, 63.3]	47.1 [35.3, 59.0]	47.6 [38.4, 56.8]	48.2 [33.9, 62.5]	47.9 [36.0, 59.8]
LIC	0.67 [0.48, 0.86]	0.55 [0.32, 0.77]	0.60 [0.37, 0.84]	0.78 [-0.01, 1.57]	0.59 [0.38, 0.80]	0.69 [0.07, 1.32]	0.74 [0.08, 1.41]	0.58 [0.36, 0.79]	0.66 [0.13, 1.19]
¹ Mean (mean±2SD)

Figure 1: Normal values (mean +- 2SD) by sex and field strength.

Note: There is an extreme outlier of Yca_074 with LIC = 3.39.

P-values comparing the normal values between sexes and fields strengths are tabulated in Table 5 and Table 6.

Table 5: P-values of t-test comparing 1.5T vs 3T by sex.
	Female	Male	Overall
PDFF	0.484	0.010	0.013
R2s	<0.001	<0.001	<0.001
T1	<0.001	0.034	<0.001
T2	0.149	0.147	0.582
LIC	<0.001	0.003	<0.001

Table 6: P-values of t-test comparing female vs male by field strength.
	1.5T	3T	Overall
PDFF	0.132	0.946	0.264
R2s	0.073	0.120	0.129
T1	0.042	<0.001	<0.001
T2	<0.001	0.988	0.041

BMI correlations

Figure 2 plots PDFF, R2*, T1, T2, and LIC against BMI.

PDFF positively correlated with BMI for both 1.5T and 3T;
T1 negatively correlated with BMI for 3T only;
No correlation of R2* or LIC with BMI;
Can fit a regression line for 1.5/3T combined if desirable.

Figure 2: Measurements as a function of BMI.

By athletic group

Normal values (Mean \(\pm\) 2SD) of PDFF, R2*, T1, T2, and LIC are plotted in Figure 3 by sport. The size of the mean dot is proportional to the group size for the sport.

Figure 3: Normal values (mean +- 2SD) by sport.

Grouping of sports are considered below.

Type	Sports
Power sport	Diver, Track athlete, Wrestler
Mixed sport	Basketball, Diver, Football, Hockey, Ice Hockey, Soccer, Softball, Tennis, Volleyball
Endurance sport	Cross country, Rower, Swimmer, Track athlete

Number of subjects in each sex, field strength and sport type combination:

	Type			Total
	Power sport	Mixed sport	Endurance sport	Total
strata
Female-1.5T	1	14	8	23
Female-3T	6	13	7	26
Male-1.5T	3	40	6	49
Male-3T	12	23	5	40
Total	22	90	26	138

Table 7: Comparison of normal values between grouped sports by sex and field strength.
	Strata	Power sport	Mixed sport	Endurance sport
PDFF	Female-1.5T	3.66 [3.66, 3.66]	2.42 [0.38, 4.47]	2.6 [-0.24, 5.43]
	Female-3T	3.92 [-4.31, 12.15]	1.62 [0.92, 2.32]	1.8 [0.77, 2.82]
	Male-1.5T	1.87 [0.59, 3.15]	3.4 [-1.69, 8.49]	2.24 [1.36, 3.12]
	Male-3T	1.91 [-0.67, 4.48]	2.24 [0.37, 4.11]	2.46 [-0.62, 5.53]
R2s	Female-1.5T	29.26 [29.26, 29.26]	31.1 [24.21, 37.98]	33.34 [25.82, 40.86]
	Female-3T	54.49 [35.32, 73.65]	39.3 [30.94, 47.66]	39.64 [34.38, 44.9]
	Male-1.5T	66.55 [-54.1, 187.2]	34.15 [25.74, 42.55]	32.97 [25.9, 40.04]
	Male-3T	43.71 [36.39, 51.03]	47.77 [28.57, 66.97]	44.46 [38.96, 49.96]
T1	Female-1.5T	589.15 [589.15, 589.15]	612.99 [502.85, 723.12]	590.2 [509.43, 670.97]
	Female-3T	724.89 [526.4, 923.39]	794.13 [599.78, 988.47]	758.4 [656.73, 860.08]
	Male-1.5T	535.45 [304.02, 766.88]	579.41 [493.57, 665.25]	590.09 [523.92, 656.27]
	Male-3T	656.86 [490.37, 823.35]	593.89 [381.49, 806.29]	614.11 [446.55, 781.67]
T2	Female-1.5T	52.99 [52.99, 52.99]	50.7 [41.91, 59.49]	49.89 [39.34, 60.44]
	Female-3T	43.36 [29.01, 57.71]	49.89 [39.67, 60.11]	49.05 [33.98, 64.13]
	Male-1.5T	43.11 [27.27, 58.95]	46.26 [39.23, 53.29]	47.65 [38.06, 57.24]
	Male-3T	44.48 [33.5, 55.46]	48.61 [32.46, 64.77]	55.11 [47.08, 63.15]
LIC	Female-1.5T	0.6 [0.6, 0.6]	0.65 [0.47, 0.83]	0.71 [0.51, 0.9]
	Female-3T	0.71 [0.45, 0.96]	0.5 [0.39, 0.61]	0.5 [0.43, 0.58]
	Male-1.5T	1.57 [-1.57, 4.71]	0.73 [0.51, 0.95]	0.7 [0.51, 0.88]
	Male-3T	0.56 [0.46, 0.66]	0.61 [0.36, 0.87]	0.57 [0.5, 0.64]

Figure 4: Normal values (mean +- 2SD) by grouped sports, sex and field strength.