Would an mri show melanoma of scalp?

Can show if larger: Mri is a good scan to assess skin/subcutaneous masses and hence can pick up variations in the tissues; however not specific for melanoma and then it will not identify if melanoma presents with just skin discoloration; it has to form a mass to be identified in the mri.

No: If you have suspicious lesions anywhere they should be checked by a physician and possibly biopsied.