Meaningful Data or Just Measurements? Differences Between Ionization Chamber and Solid-State Detectors

Abstract

One of the principal responsibilities of a clinical diagnostic medical physicist is to ensure good image quality at an appropriate dose. To determine dose, three quantities must be known for the x-ray beam: peak tube potential, half-value layer (HVL) and air kerma (AK), formerly known as exposure. Instrument and equipment setup (ie, geometric factors) are also important in finding the desired value. The gold standard for clinical exposure or AK measurements uses a calibrated air ionization chamber (IC), which is used with aluminum filters to determine HVL from additional measurements. A separate instrument is required to find the peak tube potential. Solidstate detectors (SStDs) are now available for use in diagnostic physics measurements in mammography, general radiography, and fluoroscopy. The advantage of these alternative instruments is that they can acquire measurements for multiple quantities simultaneously and record them directly into a computer database. The question is, how reliable are these measurements compared with the gold standard? Consider the following situation: You perform an image quality and dose assessment as part of your annual mammography medical physics survey. You have your trusted gold-standard instruments and a new