Tried ng-src="img/{{item.shortname}}_tn.jpg" and src="img/{{item.shortname}}_tn.jpg" with no luck. Could this be an Angular issue, possibly in ionic.bundle.js?
In app.js:
.controller('ListController', ['$scope', '$http', function($scope, $http){
$http.get('js/data.json').success(function(data){
$scope.artists = data;
});
}]);