PPI of PDF generated from an image

I will explain what I need through this scenario:  When I open a JPG file in Photoshop that is 180 PPI and then save from within Photoshop to a PDF, the resulting PDF has the same width and height because the PPI is maintained.  I need the same thing to happen when I use the QuickPDF API.  I want the PPI to be maintained and therefore the dimensions (width and height) will be maintained.  I implemented an example using the API (using AddImageFromFile, DrawImage, SaveToFile, etc.) with an image in 180 PPI and it resulted in a PDF in 72 PPI.  Therefore the width and height was much larger in the resulting PDF than the original image width and height.  How do I get the same result that Photoshop's save to PDF gives?

if (qp.AddImageFromFile(sImageFileName, 1) == 0)

return;

// Get width, height of image

int lWidth = qp.ImageWidth();

int lHeight = qp.ImageHeight();

if (qp.SetPageDimensions(lWidth, lHeight) == 0)

MessageBox.Show("Quick PDF Library was unable to process the page dimensions for " + sImageFileName);

return;

// Draw the image onto the document using the specified width/height

if (qp.DrawImage(0, lHeight, lWidth, lHeight) == 0)

MessageBox.Show("Quick PDF Library was unable to redraw the image as a PDF file.");

return;

// Then do so using a .PDF extension instead of the image filename

// in the output folder...

string sPDFFileName = "c:\\temp\\" + Path.GetFileNameWithoutExtension(sImageFileName) + ".pdf";

if (qp.SaveToFile(sPDFFileName) == 0)

MessageBox.Show("Quick PDF Library could not save the image " + sImageFileName + " as a PDF file.");

return;