fnm = 'subject42_t1w_p4.rawb';
dim = [256 256 181];

mat = [1 0 0 -128.75; 0 1 0 -146.75; 0 0 1 -73.25; 0 0 0 1];

fid = fopen(fnm);
data = fread(fid, prod(dim), 'uint8');
img = reshape(data, dim);

V = struct('fname', 'bw20.img',...
           'dim',   dim,...
           'mat',   mat,...
           'pinfo', [1;0;0],...
           'dt',    [spm_type('uint8') spm_platform('BigEnd')],...
           'n',     [1 1]...
           );
       
spm_write_vol(V, img);