2
130 m /g and are present in a dispersion in the form of colloidal units. The
polyelectrolyte has a molecular weight of 1,000 to 25,000 and has a charge
number of at least 5.0. Moreover, the relaxivities of the contrast media are such
that r is greater than
1
9 x 10 M s and the ratio of r is at least 7 under specified conditions.4 -1-1 2
THE CLAIMS
Claims 1 is illustrative of appellants’ invention and is reproduced below.
1. A dual purpose MRI contrast medium consisting essentially of an aqueous
dispersion of superparamagnetic solid particles and at least one polyelectrolyte
which acts as a dispersant, said polyelectrolyte having an average molecular weight
of from 1,000 to 25,000, said superparamagnetic solid particles having a primary
2
particle size of from 7 to 50 nm and a specific surface area of from 30 to 130 m /g
and being present in the dispersions in the form of colloidal units with on average
only one superparamagnetic solid particle enveloped by the polyelectrolyte, and said
polyelectrolyte having a charge number greater than 5, with the proviso that the
4 -1 -1
relaxivities of the contrast media are such that r is greater than 9 x 10 M s and
1
the ratio of r to r is at least 7, measured at 20 MHz and 37°C.2 1
As evidence of obviousness, the examiner relies upon the following
references.
Groman et al. 4,827,945 May 9, 1989
Pilgrimm 5,160,725 Nov. 3, 1992
klaveness et al. WO 89/11873 Dec. 14, 1989
THE REJECTION
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