Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Subjects received an intravenous injection of 1110 MBq 99mTc-ECD (ethylcysteinate dimer, Neurolite, Bristol-Myers Squibb Pharma), and were imaged by a dual-head rotating gamma camera (VG MILLENIUM GE), according with European procedure guidelines [9].
Category: