Film Screen Intravenous Subtraction Angiography

Abstract The application of intravenous angiography to arteriography is currently, and justi­ fiably, receiving much attention.1 "5 The advantages of this technique, where applicable, over the arterial approach are clear. While the application of digital equipment and procedures to intravenous angiography has stimulated interest in this technique, it should be emphasized that subtraction intravenous angiography can be performed with film-screen techniques.6 ' 7 The results obtained using film-screen techniques are generally superior to those which can be obtained with currently available digital systems. Although film-screen techniques are relatively simple to perform, appropriate films and photographic procedures must be used for optimum results. Care must be taken in mask production to include all the relevant data from the base film. The subtraction image should be printed on a film with contrast characteristics appropriate to the study. We will describe necessary photographic considerations for doing intravenous angiography simply and routinely with film-screen systems.IntroductionThere is currently much interest in the technique of introducing contrast media via the venous system as an alternative to introduction via the arterial system for some angiographic studies. The numerous advantages of Intravenous Angiography (IVA) relative to conventional arteriography make it a viable procedure for investigating large vessels (>lmm) where the relatively low concentrations of contrast media can be satisfactorily imaged. The advantages of IVA include: Less Invasive Reduced Patient Trauma and Discomfort Outpatient Procedure Lower Procedure Cost Applicability to High Risk and Asymtomatic PatientsWhile the interest in intravenous angiography has been stimulated by the advent of electronic techniques for data capture and image subtraction, we want to emphasize that this procedure can be performed easily and with excellent results using conventional film-screen systems, automatic film changers and photographic subtraction techniques. Numerous institutions are now doing film-screen IVA routinely.In this paper we discuss methods and technical considerations for obtaining good results with the film-screen approach. Some comparisons are made between the film-screen technique and the electronic (or digital) technique. We include a short discussion of the fundamental limitations to contrast sensitivity in intravenous angiography to correct the existing misconception that electronic techniques provide significantly greater contrast sensitivity than film-screen techniques.Intravenous Subtraction AngiographyIntravenous angiography involves displaying vessels with much lower concentrations of contrast media than would generally be present in conventional arteriography. The success of this approach is predicated on improvements in vessel conspicuity achieved by subtraction techniques for removing unwanted (or interfering) anatomical details. The subtraction can be performed either electronically or photographically.Fundamental Limitations in IVAThe challenge in intravenous angiography, as stated previously, is to display vessels with small concentrations of the contrast media. Therefore, contrast sensitivity has been appropriately recognized as a primary consideration. In any radiographic imaging system the fundamental limitation to contrast sensitivity is quantum noise. For any given level of contrast sensitivity there exists a corresponding maximum level of quantum noise which can be tolerated. The x-ray photon density, at the detector, necessary to obtain the required level of quantum noise is directly related to the