Bring A Large Pot Of Lightly Salted Water To A Boil. Add Pasta And Cook For 4 Minutes Or Until Al Dente; Drain. Melt Butter In A Large Heavy Skillet Over Medium Heat. Saute Shrimp For 1 Minute On Each Side. Stir In Garlic, And Cook For 1 Minute. Remove Shrimp With A Slotted Spoon; Set Aside. Stir In Flour And Cajun Seasoning. Cook, Stirring For 5 Minutes. Gradually Whisk In Milk, Then Cook Until Thickened. Remove From Heat, And Season With Salt And Lemon Juice. Return Shrimp To Sauce, And Spoon Over Cooked Pasta.