Portable X-ray radiographs are widely used in the Intensive Care Unit (ICU) for indicating significant or unexpected conditions requiring immediate changes in patient management.  A single diagnostic image may show a condition that is related to treatment procedures, such as a collapsed lung or the proper or improper placement of tubing within the patient.  A succession of diagnostic images, taken over a time period, may help to show the progress of a patient's condition and help to direct ICU treatment accordingly. 
While portable radiography has advantages for ready accessibility, however, there are some difficulties that limit the accuracy and usefulness of diagnostic images obtained in the ICU.  Differences in image quality from one image to the next can be significant, owing to differences in exposure settings, patient and apparatus positioning, scattering, and grid application.  Even for successive images obtained from the same patient over a short treatment period, there can be substantial image quality differences between two or more images that complicate or even prevent effective comparison between them, thus constraining the ability of the clinician to detect subtle changes that can be highly significant. 
An issue for patient care management relates to the ability to detect the proper positioning of tubing that has been inserted into the patient.  This tubing includes, for example, endotracheal (ET) tubes, feeding tubes (FTs), and nasogastric tubes (NGTs), among others.  Proper tube positioning can help to ensure delivery or disposal of liquids and air/gases to and from the patient during treatment.  Improper tube positioning can cause patient discomfort or can render a treatment ineffective.  In particular, because of poor image quality in portable anterior-posterior (AP) X-ray images, it is often difficult for a clinician to visually detect, with sufficient certainty, the position of the tube tip.  Thus, there is a need for a diagnostic imaging method that helps to identify tubing and tube tip position.