#!/usr/bin/perl -w
use File::Copy;
use File::Path;

use strict;
use warnings;

....
/* 
$filename, $pat_name, $study_date, $study_time, $series_num are defined
*/
....

my ($new_filename, $dir_path);

#create new pathname
$dir_path = "$pat_name/$study_date-$study_time/$series_num";
   
#create new filename
$new_filename="$pat_name-$study_date-$study_time-$series_num-$image_num.dcm";

eval { mkpath($dir_path) }; 
if ($@) {
   print "Couldn't create $dir_path: $@";
}

$new_filename = "$dir_path/$new_filename";


rename($filename,$new_filename) or die( "could not rename $filename to $new_filename: $!\n" );