A 39-year-old Polish man comes to the clinic for painful calves after walking long distances and for discoloration of the fingers with changes in temperature. He says his symptoms started two months ago, and he gets no relief from the ibuprofen. He has previously been healthy. He currently smokes a pack a day and drinks socially. He has no history of drug abuse. On physical examination, his blood pressure is 140/90 mm Hg, heart rate is 68/min, and he is afebrile. Examination of the hands reveals distal digital ischemia and trophic changes in the nails of both hands. Radial pulses are absent bilaterally, but all other pulses are present. His right calf shows evidence of a superficial thrombophlebitis. Laboratory studies show: white cell count 9,600/mm3, hematocrit 38.6%, MCV 89 μm3, ESR 40 mm/h, and C-ANCA as negative. The rheumatoid factor and ANA are negative. Which of the following should be done next for this patient?