Table 2. Relaxivity Measurements of Gd-C4-IA and Gd(III)-Labeled Protein Cages at 1.4 and 7 T^a.

	1.4 T at 37 °C		7 T at 25 °C
sample name	r1,ionic(mM–1 s–1)	r1,particle(mM–1 s–1)	r1,ionic(mM–1 s–1)	r1,particle(mM–1 s–1)
Gd-C4-IAb	4.2	N/A	2.6	N/A
Gd-C4-IAc	4.1	N/A	3.2	N/A
Gd-AaLS-13b	18.3	2727	8.0	1192
Gd-OP-3intCc	15.9	525	5.3	175
Gd-OP-2intCc	18.0	419	5.4	124
Gd-OP-1intCc	15.0	165	4.6	51
Gd-OP-1extCc	11.2	157	4.9	69

^aRelaxation times (T₁) were measured with error of <5%, while standard deviations of [Gd(III)] were determined by ICP-MS of triplicate samples.

^bRelaxivity data in 50 mM sodium phosphate (pH 8.0), 200 mM NaCl, 5 mM EDTA.

^cRelaxivity data in 25 mM Tris (pH 7.6), 200 mM NaCl, 5 mM EDTA.