TableView scroll is choppy

I put UIImageViews into my table view cells and scrolling has been very choppy. I'm assuming it's because the images are being reloaded each time their cell appears, but how would I preload/cache the images? Thanks for your help.

Code:

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    
    NSString *CellIdentifier = @"Cell";
    
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:CellIdentifier] autorelease];
    }
    
    
    // Set up the cell...
	NSDictionary *dic = [self.issues objectAtIndex:indexPath.row];
        
    cell.text = [dic objectForKey:@"Date"];
    
    cell.imageView.image = [UIImage imageWithContentsOfFile:[NSString stringWithFormat:@"%@/issues/%@/cover.png", documentsDirectory, [dic objectForKey:@"Directory Name"]]];
    
    return cell;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    
        return 150;
    
}

 

Do you know the name of it?