Françoise Barré-Sinoussi "for their discovery of human immunodeficiency virus". The omission of Robert Gallo was controversial: 106 scientists signed a letter to the journal Science stating that "While these awardees fully deserve the award, it is equally important to recognize the contributions of Robert C. Gallo", which "warrant equal recognition". Montagnier said that he was "surprised" that the award had not been shared with Gallo. 2006 The 2006 prize went to Andrew Fire and Craig C. Mello "for their discovery of RNA interference—gene silencing by double-stranded RNA". Many of the discoveries credited by the committee to Fire and Mello, who studied RNA interference in Caenorhabditis elegans, had been previously studied by plant biologists, and it was suggested that at least one plant biologist, such as David Baulcombe, should have been awarded a share of the prize. 2003 The 2003 prize was awarded to Paul Lauterbur and Sir Peter Mansfield "for their discoveries concerning magnetic resonance imaging" (MRI). Two independent alternatives have been alleged. Raymond Damadian first reported that nuclear magnetic resonance (NMR) could distinguish in vitro between cancerous and non-cancerous tissues on the basis of different proton relaxation times. He later translated this into the first human scan. Damadian's original report prompted Lauterbur to develop NMR into the present method. Damadian took out large advertisements in an international newspapers protesting his exclusion. Some researchers felt that Damadian's work deserved at least equal credit. Separately, Herman Y. Carr both pioneered the NMR gradient technique and demonstrated rudimentary MRI imaging in the 1950s. The Nobel prize winners had almost certainly seen Carr's work, but did not cite it. Consequently, the prize committee very likely was unaware of Carr's discoveries, a situation likely abetted by Damadian's campaign. Mansfield said in his autobiography that "the person who really missed out" the prize was Erwin Hahn for his contribution to the principles of spin echoes. 1998 The Nobel Prize for Physiology or Medicine was awarded in 1998 to Robert Furchgott, Louis Ignarro and Ferid Murad "for their discoveries concerning nitric oxide as a signalling molecule in the cardiovascular system". There followed protest by the scientific community due to the omission of Salvador Moncada, who was internationally recognised as the major contributor to the discovery of this field together with Robert Furchgott. 1997 The 1997 prize was awarded to Dr. Stanley B. Prusiner for his discovery of prions. This award caused a long stream of polemics.