Pet scan not showing liver

My Dad has been diagnosed with liver cancer.  He has a mass 7.9cm by 6.7cm in the hepatic dome with four other small nodules.  He has HepC close to 20 years now and 8 years ago they found this mass and he unfortunately left it alone.  So... her we are.  He had a Petscan done Friday and the doc called him at home at 9pm to see if he is feeling okay and said he couldn't see the liver on the scan and he is concerned it may be bleeding or be filed with blood.  He wants a MRI stat on Monday.  What could be of all of this.  I am confused.  He is complaining of back pain and feels tired and weak.  His lower legs are bluish/purple and swollen????? Please give me any info.  Thanks.