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 characteristics and mean values of PDFF, R2*, T1, and T2 are provided by sex and overall in Table 1 below.

Table 1:
Subject characteristics and measurements by sex.
Characteristic	Female, N = 64¹	Male, N = 109¹	Overall, N = 173¹
Age	19.0 (18.7, 20.7)	19.0 (19.0, 21.0)	19.0 (19.0, 20.9)
Athlete Type
Basketball	3 (4.7%)	4 (3.7%)	7 (4.0%)
Cross country	0 (0%)	3 (2.8%)	3 (1.7%)
Diver	1 (1.6%)	0 (0%)	1 (0.6%)
Football	0 (0%)	57 (52%)	57 (33%)
Hockey	1 (1.6%)	0 (0%)	1 (0.6%)
Ice Hockey	11 (17%)	11 (10%)	22 (13%)
Rower	19 (30%)	9 (8.3%)	28 (16%)
Soccer	6 (9.4%)	6 (5.5%)	12 (6.9%)
Softball	5 (7.8%)	0 (0%)	5 (2.9%)
Swimmer	1 (1.6%)	2 (1.8%)	3 (1.7%)
Tennis	1 (1.6%)	1 (0.9%)	2 (1.2%)
Track athlete	9 (14%)	9 (8.3%)	18 (10%)
Volleyball	7 (11%)	0 (0%)	7 (4.0%)
Wrestler	0 (0%)	7 (6.4%)	7 (4.0%)
Height (cm)	172.0 (165.0, 180.0)	188.0 (183.0, 195.3)	183.0 (173.9, 191.0)
(Missing)	3	6	9
Weight (kg)	69.6 (63.1, 76.1)	91.5 (80.8, 108.9)	82.0 (69.5, 99.0)
(Missing)	2	5	7
BMI	23.2 (21.7, 25.1)	26.0 (23.3, 30.5)	24.7 (22.5, 27.7)
(Missing)	3	7	10
Field Strength
1.5T	27 (42%)	60 (55%)	87 (50%)
3T	37 (58%)	49 (45%)	86 (50%)
PDFF	1.8 (1.6, 2.3)	2.1 (1.8, 2.8)	2.0 (1.7, 2.6)
(Missing)	12	17	29
R2s	36.3 (32.2, 41.3)	37.1 (32.7, 43.9)	36.7 (32.7, 43.1)
(Missing)	12	17	29
T1	707.7 (596.4, 793.5)	586.6 (549.4, 646.8)	614.6 (562.8, 711.3)
(Missing)	1	1	2
T2	49.7 (45.2, 53.1)	46.7 (44.0, 50.5)	47.2 (44.4, 51.4)
(Missing)	12	17	29
¹ Median (IQR); n (%)

Normal values by sex and field strength

Normal values (Mean \(\pm\) 2SD) of PDFF, R2*, T1, and T2 are summarized overall and by sex and field strength in Table 2 and shown graphically in Figure 1. (Female 3T of T1 appears somewhat outlying.)

Table 2:
Normal values by sex and field strength.
	Female			Male			Overall
	1.5T, N = 27¹	3T, N = 37¹	Overall, N = 64¹	1.5T, N = 60¹	3T, N = 49¹	Overall, N = 109¹	1.5T, N = 87¹	3T, N = 86¹	Overall, N = 173¹
PDFF	2.5 [0.2, 4.8]	2.2 [-1.9, 6.2]	2.3 [-1.0, 5.7]	3.1 [-1.5, 7.8]	2.2 [0.0, 4.4]	2.7 [-1.2, 6.6]	2.9 [-1.1, 7.0]	2.2 [-0.9, 5.2]	2.6 [-1.1, 6.2]
R2s	32 [25, 39]	43 [26, 59]	38 [21, 54]	36 [6, 66]	46 [30, 62]	40 [14, 67]	35 [9, 60]	45 [29, 61]	39 [16, 63]
T1	597 [491, 702]	776 [617, 935]	699 [473, 925]	581 [489, 672]	628 [435, 820]	602 [450, 753]	586 [489, 682]	691 [460, 922]	637 [432, 843]
T2	50.6 [41.7, 59.5]	48.1 [35.2, 61.1]	49.3 [37.8, 60.7]	46 [38, 54]	48 [33, 63]	47 [35, 59]	47.7 [38.6, 56.9]	48.2 [34.2, 62.2]	48.0 [36.2, 59.7]
¹ Mean (mean±2SD)

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

Comparison between types of sport

Normal values (Mean \(\pm\) 2SD) of PDFF, R2*, T1, and T2 are plotted in Figure 2 by sport. The size of the mean dot is proportional to the group size for the sport (the actual numbers are in Table 1).

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

Groupings of sports are considered below.

Grouping option 1

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

Table 3:
Comparison of normal values between grouped sports by option 1.
	Skill sport, N = 1¹	Power sport, N = 7¹	Mixed sport, N = 113¹	Endurance sport, N = 52¹	p-value²
PDFF	11.8 [11.8, 11.8]	1.3 [0.5, 2.0]	2.7 [-1.1, 6.4]	2.3 [0.0, 4.6]	<0.001
R2s	51 [51, 51]	60 [-16, 135]	38 [21, 55]	40 [22, 57]	<0.001
T1	870 [870, 870]	609 [357, 862]	630 [425, 834]	653 [462, 844]	0.056
T2	50.2 [50.2, 50.2]	39.8 [28.8, 50.8]	48.1 [37.1, 59.0]	48.8 [36.6, 61.1]	0.005
¹ Mean (mean±2SD)
² One-way ANOVA

Figure 3: Normal values (mean +- 2SD) by grouped sports under option 1.

Grouping option 2

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

Table 4:
Comparison of normal values between grouped sports by option 2.
	Quick burst, N = 95¹	Endurance, N = 78¹	p-value²
PDFF	2.9 [-1.5, 7.3]	2.1 [0.0, 4.2]	0.016
R2s	38 [20, 55]	42 [12, 71]	0.061
T1	620 [416, 825]	658 [459, 858]	0.015
T2	48.3 [37.0, 59.6]	47.5 [35.1, 59.9]	0.4
¹ Mean (mean±2SD)
² One-way ANOVA

Figure 4: Normal values (mean +- 2SD) by grouped sports under option 2.

Grouping option 3 (dynamic)

Type	Sports
Low	Diver
Moderate	Football, Softball, Tennis, Volleyball, Wrestler
High	Basketball, Cross country, Hockey, Ice Hockey, Rower, Soccer, Swimmer, Track athlete

Table 5:
Comparison of normal values between grouped sports by option 3 (dynamic).
	Low, N = 1¹	Moderate, N = 78¹	High, N = 94¹	p-value²
PDFF	11.8 [11.8, 11.8]	2.8 [-1.5, 7.0]	2.2 [0.2, 4.3]	<0.001
R2s	51 [51, 51]	40 [11, 69]	39 [23, 55]	0.5
T1	870 [870, 870]	613 [433, 793]	655 [442, 868]	0.002
T2	50.2 [50.2, 50.2]	46.5 [36.5, 56.4]	49.3 [36.6, 62.1]	0.012
¹ Mean (mean±2SD)
² One-way ANOVA

Figure 5: Normal values (mean +- 2SD) by grouped sports under option 3 (dynamic).

Grouping option 4 (static)

Type	Sports
Low	Cross country, Hockey, Soccer, Softball, Tennis, Volleyball
Moderate	Basketball, Football, Ice Hockey, Swimmer, Track athlete
High	Diver, Rower, Wrestler

Table 6:
Comparison of normal values between grouped sports by option 4 (static).
	Low, N = 30¹	Moderate, N = 107¹	High, N = 36¹	p-value²
PDFF	1.9 [0.9, 2.9]	2.8 [-1.1, 6.8]	2.3 [-1.7, 6.3]	0.048
R2s	37 [25, 50]	39 [20, 58]	42 [4, 79]	0.3
T1	679 [476, 883]	625 [427, 822]	641 [427, 856]	0.038
T2	48.4 [39.7, 57.1]	47.9 [36.1, 59.8]	47.7 [33.9, 61.4]	0.9
¹ Mean (mean±2SD)
² One-way ANOVA

Figure 6: Normal values (mean +- 2SD) by grouped sports under option 4 (static).