Table 1.

Characteristics of candidate elements for CT contrast agents [46–49]. Please see legend of Fig. 13 for notations on highlighted and colored text.

Atomic number (Z)	Name	Symbol	K edge (keV)	Annual production (metric tons)	Raw cost of material per 30 g dose (USD)		Concerns*
53	Iodine	I	33.2	>30,000	<1		I >100 kVp
54	Xenon	Xe	34.6	<1			G
55	Cesium	Cs	36.0	<20	>600		T
56	Barium	Ba	37.4	6,000,000	<1	BaSO4	T for IV
57	Lanthanum	La	38.9	12,000	<1	La2O3
58	Cerium	Ce	40.4	23,000	<1	CeO2
59	Praseodymium	Pr	42.0	2,500	<1	Pr6O11
60	Neodymium	Nd	43.5	7,000	<3	Nd2O3
61	Promethium	Pm	45.2				Synthetic
62	Samarium	Sm	46.8	700	<1	Sm2O3	A
63	Europium	Eu	48.5	100	<30	Eu2O3	C, A
64	Gadolinium	Gd	50.2	400	<1	Gd2O3	T, A
65	Terbium	Tb	52.0	10	<30	Tb4O7	C, A
66	Dysprosium	Dy	53.8	100	<20	Dy2O3	C, A
67	Holmium	Ho	55.6	10	<1	Ho2O3	A
68	Erbium	Er	57.5	500	<1	Er2O3	A
69	Thulium	Tm	59.4	50	<1	Tm2O3	A
70	Ytterbium	Yb	61.3	50	<1	Yb2O3	T, A
71	Lutetium	Lu	63.3	10	<50	Lu2O3	C, A
72	Hafnium	Hf	65.3	50	<20	HfO2	C, A
73	Tantalum	Ta	67.4	>1,200	<1	Ta2O5	I <90 kVp
74	Tungsten	W	69.5				T
75	Rhenium	Re	71.7	49	>100		C, A
76	Osmium	Os	73.9	<1			C, A
77	Iridium	Ir	76.1	3	>500		C, A
78	Platinum	Pt	78.4	160	>1,000		C, A
79	Gold	Au	80.7	2,800	>1,000		C, I
80	Mercury	Hg	83.1				High T
81	Thallium	Tl	83.5				High T
82	Lead	Pb	88.0				High T
83	Bismuth	Bi	90.5	8,500	<1		I
84	Polonium	Po	93.1				High R

^*G – Gas; no stable solid compounds at room temperature

T – Toxicity

C – Cost

A – Availability

I – Imaging performance

R – Radioactivity (toxic)