In recent years, there have been tremendous ad-vances in understanding the pathophysiology and mechanisms of pain; concurrently, there have been enormous advances in diagnostic imaging. Diagnostic imaging is an essential tool for the pain practitioner, who uses it to understand, diagnose, and treat pain. Although plain x-rays remain the mainstay of diagnostic imaging, advanced modalities including computed tomography (CT), magnetic resonance imaging (MRI), and nuclear medicine studies have proven to be extremely valuable diagnostic tools for patients with pain. Consultation with a radiologist or imaging specialist often aids in choosing the most cost-effective test for establishing a diagnosis and in understanding the underlying pathology.
Plain Film Radiology: X-rays
Plain x-rays (static x-rays) generate two-dimensional (2D) images that primarily display skeletal tissue, but in addition soft tissue anatomy is either seen or inferred. Contemporary x-ray technology generally produces high-quality images with minimal radiation exposure. Radiopaque contrast materials given orally, locally, intravenously, and intrathecally may be used to aid the study. Most contrast materials used with plain x-rays are iodine-based. Plain x-rays remain the first-line examination for many conditions.
Today’s fourth-generation scanners have significantly improved quality, and the imaging time is significantly shortened compared to early CT scanners. In CT imaging, the x-ray tube produces a beam of energy that passes through a single section of the patient. This beam is then detected by a circular array of detectors on the opposite side. Both the detector and the x-ray source rotate around an axis of the patient and produce exposures at small intervals of rotation. Subsequently, computer reconstruction results in a display of the targeted area. The resolution can be as small as 0.5 mm. Intravenous contrast can be used to enhance the imaging of vascular structures as well as normal tissues.
CT displays soft tissues fairly well and is used for soft tissue imaging if MRI (which provides superior soft tissue contrast) is not available, or if the patient cannot tolerate MRI because of claustrophobia or because it is a more lengthy process.
Magnetic Resonance Imaging: MRI
A significant difference between MRI scanning and CT and x-rays is that MRI uses no ionizing radiation. In MRI, signals are obtained by subjecting the tissues to strong magnetic fields, which influence hydrogen ions in the tissues to align in a certain direction. Tiny radiofrequency signals are emitted as the hydrogen ions “relax” when the magnetic field is removed. The image represents the intensities of the electromagnetic signals emitted from the hydrogen nuclei in the patient. A tissue such as fat, which is rich in hydrogen ions, gives a bright signal, whereas bone gives a void, or essentially no signal. Abnormal tissue generally has more free water and displays different MR characteristics.
MRI is easily able to provide multiplanar images. Its advantage over CT is its superior contrast of soft tissues, especially neural tissue. The addition of gadolinium as a contrast material aids in defining tumors and inflammatory processes.
Bone scans and nuclear medicine
Bone scans are commonly used to evaluate complaints of skeletal pain. Bone scans are more sensitive than x-rays in detecting skeletal pathology. One third of patients with pain and known malignant disease with normal x-rays have metastatic lesions on bone scans.
Nuclear medicine uses the tracer principle, which essentially tags certain physiologic substances in the body and measures its distribution and flow or its presence in a target system. A radiopharmaceutical agent is injected into the patient and the radioactive decay is detected by a detection device, for example, a gamma counter.
In positron-emission tomography (PET), positron emissions are detected with a circular array of detectors. The number of decays is displayed to produce an image of specific metabolic processes. PET is an excellent tool for quantification of various metabolic and physiologic changes and processes, making it a functional imaging device. The collection of literature about PET scanning and functional neuroimaging of pain processes is increasing.
NDIC offers a variety of diagnostic and imaging services to assess the source, cause and intensity of a wide variety of acute and chronic pain conditions. Our diagnostic and imaging services for pain treatment and management include x-rays, CT, MRI, nuclear medicine and bone scans, among other tests. For more information about services and tests available at NDIC call 239-593-4200. To schedule an appointment call 239-593-4222.