PictureBox stops adding images - vb.net

Question

I am using a worker thread to load .png images (from a path string) into a global PictureBox2 object, and then exit the _RunWorkerCompleted to use the PictureBox2's width and height for additional work in the method called processpic2. Everything works fine until about the 5th or 6th images were added to the PB. A this point, in the processpic2 method, an exception is thrown since the image property of the PictureBox2 evaluates to nothing.
Why would a PB stop taking images after a while?
Public Class Form1
Public WithEvents BackgroundWorker1 As New System.ComponentModel.BackgroundWorker
Private Sub BackGroundworker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Dim args As ArgumentType = e.Argument
PictureBox2.Image = Nothing
PictureBox2.Invalidate()
Dim img As Image
Using str As Stream = File.OpenRead(args._pathstr)
img = Image.FromStream(str)
End Using
PictureBox2.Image = img
e.Result = "done"
End Sub
Private Sub BackgroundWorker1_RunWorkerCompleted(ByVal sender As System.Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) _Handles BackgroundWorker1.RunWorkerCompleted
'Called when the BackgroundWorker is completed.
processpic2()
End Sub
Sub btnLoadPicture(pathstr)
Dim args As ArgumentType = New ArgumentType()
args._pathstr = pathstr
BackgroundWorker1.RunWorkerAsync(args)
End Sub
Sub processpic2()
If PictureBox2.Image Is Nothing Then MsgBox("Image is Nothing")
End Sub

Answer 1

The whole point of a BackgroundWorker is to do background work. Making changes to the UI is the exact opposite of background work. It is foreground work. If your task is to clear the current contents of a PictureBox, load an image from a file and then display that image, only the middle step is background work so only the middle step should be done in the DoWork event handler. The first step should be done before you call RunWorkerAsync and the last step should be done in the RunWorkerCompleted event handler.
Having said all that, why use a BackgroundWorker at all in this case? Why not simply call the LoadAsync method of the PictureBox itself?

Answer 2

SOLUTION - thanks to the suggestions received, and what I found on MSDN regarding the LoadAsync method of PictureBox the following code solved the issue:
PictureBox2.Image = Nothing
PictureBox2.WaitOnLoad = False
' Load the image asynchronously.
PictureBox2.LoadAsync(pathstr)