cell image is resized on load TableView

I have the following detail.

I have a series of TableViews, in whose cells I am loading background images, like so:

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {



    let cell = tableView.dequeueReusableCellWithIdentifier("Cell") as! MenuSecundarioTVCell
    let seccion = items[indexPath.row]


        cell.titulo?.text = (seccion.value["nombre"] as! String)
        //PONIENDO IMAGEN DE FONDO A CELDA
        let imageBackground = UIImageView(frame: CGRectMake(0, 0, cell.frame.width , cell.frame.height+1))
        if let imageRemote = seccion.value["imageBackground"]{
            imageRemoteURL = NSURL(string: imageRemote as! String)
            imageBackground.sd_setImageWithURL(imageRemoteURL!)
            cell.backgroundView = UIView()
            cell.backgroundView!.addSubview(imageBackground)
        }
        //TERMINANDO DE PONER IMAGEN DE FONDO A CELDA

    return cell
}

I am using SDWebImage . The problem is that when the images are loaded into the cells they look like this:

After performing another action such as sliding the cells down or selecting the cell to go to the next view, when returning the image is rearranged in the correct way:

the images are test and it is clear that the resolution of the images does not match the height of the cells (120)

 override func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
        return 120
    }

Will the origin of the problem be that the resolution of the images must match the size of the cells? I have seen this problem in some apps published in the appstore but the rearrangement is so fast that it is almost unnoticeable.