To Prepare Artichokes: Pour about 3 inches water into saucepan (not aluminum or cast-iron) that is just large enough to hold artichokes snugly; add lemon juice and salt and stand artichokes upright in pan.
Cover pan and let simmer until bases of artichokes can be pierced easily with a fork, about 35 minutes.
Remove artichokes from liquid and stand upside down to drain.
When artichokes have drained thoroughly, cut each in half lengthwise; remove and discard choke and tough outer leaves.
To Prepare Filling: In medium bowl combine all ingredients for filling except crab meat; stir in crab meat, stirring until thoroughly coated with dressing.
Stuff each artichoke half with 1/4 of the filling; transfer to serving plate, cover with plastic wrap, and refrigerate until well chilled.
Variation: Substitute plain low-fat yogurt for the sour cream; reduce Optional Exchange to 10 calories.