More distal IV locations often do not tolerate 14 to 20 gauge needles and, if utilized, see a higher rate of contrast extravasation and associated complications. The utilization of power injectors depends on the gauge of the catheter and the flow limits. Power injectors are machines often built into or controlled by the CT scanner that injects the contrast at a preselected rate, length of time, and volume to meet needed imaging requirements for the desired clinical question. This location tolerates sizes adequate for the use of power injectors. The most common site for placement of the IV catheter is the antecubital fossa. Larger catheters in larger veins allow a faster rate of administration and larger volumes of contrast to be delivered. The injection of intravenous contrast typically occurs through peripherally inserted IV catheters. This article will be limited to administration intravenously (IV). Intravascular phases can be arterial, venous, or lymphatic. A contrast medium can be utilized internally or externally to a patient, and administration is frequently enterally or intravascularly. Additional, less commonly utilized contrast agents, including fluoroscopy-based air or CO2, and molecular imaging (nuclear imaging), will not be discussed in depth here. The two largest groups include CT and magnetic resonance imaging (MRI) agents. The contrast groups are not interchangeable. Various types of contrast media are useful in medical imaging. A material added to delineate or better discern these otherwise subtle findings is called contrast media. While technique can be manipulated to maximize some of the tissue’s characteristics, the pathology or tissue of concern may be beyond the contrast resolution of the system unless there is introduction of outside variables. The physical density, atomic structure, and location of lung parenchyma are different from the bones. Different techniques are utilized to evaluate for a rib fracture versus pneumonia, despite both studies covering the same anatomical structures. By changing the beam’s wavelength, amplitude, and frequency, inherent contrast can be maximized. The variables contributing to the signal loss include both the energy beam’s and the target’s physical properties. Radiographs and consequently computed tomography (CT) reflect how a target tissue depletes an energy signal as it passes through the tissue. The optimal use of contrast will depend on the modality and physics of the imaging system. To increase the contrast of these very similar tissues, an agent can be used to change the appearance of the target tissue, the background tissue, or both. Radiographs easily define bones against a background of muscle and fat, but identifying early hepatocellular carcinoma from a background of a nodular cirrhotic liver is limited using routine CT imaging. While specific anatomical structures have inherent contrast due to their physical properties, others are naturally poorly delineated. The ability to distinguish target tissue from the surrounding structures is how anatomy is defined, pathology identified, and diagnoses are made. Contrast allowed Marie Curie to identify her bones from the outline of her hand. In medical imaging, it allows adjacent substances or tissue to be distinguishable and visualized. Contrast is simply the ability to distinguish two objects. The concept of contrast is the foundation upon which imaging rests.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |