Computed tomography ( CT ) is a sensitive method for diagnosing stomach diseases. This is often used to determine the stage of cancer and keep abreast of it. It is also a useful test for investigating acute abdominal pain (especially in the lower quadrant, whereas ultrasound is the preferred first-line examination for upper right quadrant pain). Kidney stones, appendicitis, pancreatitis, diverticulitis, abdominal aortic aneurysms, and intestinal obstruction are conditions that are easily diagnosed and assessed by CT. CT is also the first path to detect solid organ injury after trauma.
Video Computed tomography of the abdomen and pelvis
Benefits
Multidetector CT (MDCT) can clearly describe anatomical structures in the stomach, which are essential in the diagnosis of internal diaphragms and nonpalpable or unpredictable hernia. MDCT also offers a clear detail of the abdominal wall that allows the wall of the hernia to be accurately identified.
Maps Computed tomography of the abdomen and pelvis
Contrast administration
Abdominal imaging is associated with many potential uses for different CT contrast phases. The majority of abdominal and pelvic CTs may be performed using a single phase, but evaluation of some types of tumors (liver/pancreas/renal), urinary collection system, and trauma patients, among others, may be best done in several phases.
In discussing the various phases and indications for CT, it should be noted that the best patient care requires individualized CT protocols based on the specific symptoms of each patient, pathology, and underlying comorbidities. Although labor-intensive, this provides the highest possible accurate diagnosis with the lowest required radiation dose. The following discussion will outline the current best practices, but not all clinical scenarios can be justified. Note that the ACR conformance criteria can be found on the ACR website (http://www.acr.org/ac).
Improved CT scan contrast can be obtained at various time points after intravenous contrast injection (time depends on the required contrast enhancement phase and organ system being evaluated). Time must be chosen specifically to optimize contrast distribution within the relevant organ parenchyma.
CT Unenhanced
Non-contrast CT scans Figure 1a (left) and 1b (right) are of limited use for soft tissue structure differentiation. However, substances such as blood, calcium (kidney stones, vascular atherosclerosis), bone, and pulmonary parenchyma are highly visible and can usually be adequately assessed with non-contrast CT. For example, in the abdomen and pelvis, there are some indications for non-contrast imaging. These include: evaluation of kidney stones; assessment for intra-abdominal bleeding; and post-endostent volume measurements. In addition, non-contrast images are often obtained simultaneously with enhanced contrast images in evaluating potential kidney transplant donors and in the evaluation of the pancreas (in combination with the contrast phase). Of note, dual-energy CT and virtual development of "non-contrast" images can ultimately avoid a combination of scans. In addition, CT angiographic examination is performed for pathology such as aneurysms and dissection is often performed simultaneously with non-contrast imaging. Unconfortable images facilitate the differentiation of active extravasation or acute bleeding from vascular calcification.
Porta vein phase
The most common technique is to perform portal vein imaging in the abdomen and pelvis (about 60-90 seconds after contrast, Figure 2). This results in almost optimal opacity contrast from most of the abdominal organs and is used for a variety of indications: nonspecific abdominal pain; hernia; infection; mass (with some exceptions such as hypervascular, renal, and some liver tumors); and in most follow-up examinations. As a general rule, this single phase is adequate unless there are specific clinical indications that have proven beneficial from other phases.
Early arterial phase (CT angiography
CT angiography (CTA) is highly effective for evaluation of arterial systems, and has largely replaced conventional angiography due to lower risk profiles and ability to survey the entire stomach. The image is obtained after a rapid bolus of intravenous contrast material (3-7 cc/s) during the arterial phase (15-35 seconds after injection) when the concentration of the contrast material in the arterial system is high (number 3). Images are typically obtained using a narrow collimation (& lt; 1 mm) and can be reconstructed retrospectively using workstations and special 3-dimensional software. CTA is commonly used in the head and chest in the evaluation of pulmonary embolism, aneurysm, vascular malformations, dissection, bleeding and ischaemia. Indications for early arterial phase imaging include: evaluation of aneurysms or dissection (cerebral, aortic, etc.), anatomy of the hepatic artery, splanchnic or kidney, and arterial imaging in liver or kidney transplants. Single-phase arterial imaging is often used in the evaluation of trauma patients either chest/abdominal/pelvic examinations complete with chest-arterial phase imaging and venous/pelvic venous phase imaging or only the venous phase of the abdominal and pelvic ports depending on the mechanism and severity of the trauma. CTA is also common in the abdomen and pelvis to evaluate vascular malformations and in bleeding evaluation. Mesenteric ischemia can also be evaluated using CT angiography. CTA of the abdomen and pelvis is often performed in combination with CTA to evaluate the limb vessels.
Final artery phase
The final arterial phase of the time is adjusted to the peak concentration of the contrast material in a high vascular tumor and takes approximately 20-35 seconds after intravenous contrast injection. Early arterial phase imaging is mostly used for angiography and will be discussed separately. Final arterial phase imaging is almost always done in conjunction with other phases (eg portal venous phase) to allow for a more complete characterization of any identified abnormality (figure 4). The primary indications for the final arterial phase are for the evaluation of liver hypervascular tumors such as hepatocellular carcinoma or hypervascular metastases (figure 4). Typical hypervascular tumors to be used include: hepatocellular carcinoma; Kidney cell carcinoma; melanoma; carcinoid/neuroendocrine tumors; some sarcomas; choriocarcinoma; and thyroid carcinoma. Although the "hypervascular", biphasic evaluation will generally be used for these patients, note that single phase is often sufficient to follow up the imaging.
Systemic venous phase
The specific CT imaging for vein structures performed is not uncommon. Most of the vein structures of some opacities on routine contrast improve the image and are sufficient for most of the examinations. However, sometimes evaluation of the inferior vena cava is desirable, such as before the placement/release of IVC filters or evaluation of IVC thrombosis.
Pending phase
Pending phase imaging (Figure 5) includes scans at different times after contrast, and depending on the pathology concerned. Typical delayed imaging time ranges from a few minutes to 15 minutes or longer. The most common indications for delayed phase imaging are kidney evaluation, collection system (ureter and bladder) and specific kidney, liver, and adrenal tumors. Renal, ureter and bladder evaluations were discussed separately in the renal imaging section. Cholangiocarcinoma occurring within extrahepatic biliary trees or intrahepatic cholangiocarcinoma is a common reason for delayed imaging. Cholangiocarcinoma is a slowly increasing fibrotic tumor, and is usually imaged after a 10-15 minute delay. Similarly, adrenal masses may be evaluated by multiphase imaging including non-enhanced CT, portal venous phase and 10 minute CT delay allowing for evaluation and improvement calculations and washout characteristics helpful in distinguishing benign adenomas from other adrenal masses.
Beyond mass evaluation, delayed phase images can be used in the evaluation of active vascular extravasation in trauma patients, vascular malformations, and aneurysm disorders.
Organ-specific considerations
Mass of heart
When evaluating liver mass, it may be advantageous to have a picture of late and arterial arterial venous phases (biphasic imaging, figure 4) because some tumors increase rapidly during the arterial phase (hepatocellular carcinoma, hepatic adenoma, follicular nodular hyperplasia (FNH), and hypervascular metastasis) but may be occult or difficult to characterize on portal vein only imaging alone (figure 6). However, it should be emphasized that the addition of the final arterial phase image is indicated only if one of these tumors is suspected, or if there is a need for further characterization of liver mass, since most patients will not benefit from the addition of this phase. In addition, if there is a need to define definite liver mass, MRI is generally more sensitive and specific, with no associated radiation dose.
The difference in temporal liver attenuation in the arterial phase may resemble liver disease.
Kidney mass
Detection and characterization of renal parenchymal masses is a frequent indication for CT. Early non-contrast CT is important for detecting calcium or fat in the lesions, and to provide the basic damping of any renal mass. After non-contrast scan, intravenous contrast is injected and the corticomedullary phase is obtained for about 70 seconds (figure 7a, 7b). The corticomedullary phase is characterized by increased renal cortex as well as renal vascularization. This phase is useful in the evaluation of benign renal variants, lymphadenopathy and blood vessels, but certain medullary renal masses may not be visible during this phase because of the minimal increase in medulla and collection systems. The parenchyma phase is obtained about 100-200 seconds after the injection of the contrast material (Figure 7c). Parenchymal phase imaging shows continued improvement of the cortex, medullary elevation, and various levels of contrast material in the collection system. The phase of parenchyma is essential for the detection and characterization of renal masses, parenchymal abnormalities, and renal collecting systems. This imaging method does not evaluate the abnormalities of the collection system.
Common kidney masses can sometimes be distinguished from each other using this imaging technique. Kidney cell carcinoma and oncocytomas usually show intense heterogeneous elevations in parenchymal phase images and are indistinguishable from each other but can be distinguished from other renal masses. Angiomyolipomas (AML's) also show an intense contrast increase but characteristically contain detectable macroscopic fat in non-contrast images, and may help differentiate AML from renal cell carcinoma and oncocytomas. Kidney lymphoma on the other hand, will often experience a decreased increase when compared with renal parenchyma in the phase images of parenchyma.
CT urography
CT urography (CTU) is commonly used in the evaluation of hematuria, and is specifically tailored to the drawing of renal, ureter and bladder collection systems in addition to the renal parenchyma. Early imaging included a non-contrast phase for detecting kidney stones as a source of hematuria. Note that dual energy CT ultimately allows the non-contrast phase to be eliminated. The contrast improvement techniques for CTU vary from institution to institution. The common techniques used in our institution and the other are double bolus, single phase imaging algorithms. This technique is a hybrid injection contrast strategy that results in renal parenchymal turbidity (parenchyma phase, figure 8a) and collection system, ureters, and bladder (excretory phase, figures 8b and 8c). At our institution, a small contrast bolus is given initially, followed by 10 minutes later with a larger bolus imaged in the corticomedullary phase. This ensures that the contrast is excreted by the kidneys and thus the collecting system undergoes opacity (the excretory phase) of the initial injection, and that the renal parenchyma also increases from the second injection (parenchyma phase). At the end of the urographic protocol, we also performed a scout image in the supine and prone position to allow for a global evaluation of the collection system. Imaging of the excretory phase allows for not only the evaluation of ureteral lumen, but also periureter abnormalities including external mass and lymphadenopathy.
Pancreatic mass
Pancreatic masses are often evaluated using both the initial artery (to evaluate vascular involvement and thus resecability, Figure 9a) and the later "pancreatic" phase (which optimizes the increase of the pancreatic parenchyma and thus best to distinguish pancreatic tumors from the parenchymal pancreas, Figure 9b). ). Pancreatic adenocarcinoma is usually hypoenhancing when compared with surrounding parenchyma. Most other common hypervascular pancreatic tumors with an increase in avid (like pancreatic neuroendocrine tumors) and appear brighter than the surrounding pancreatic parenchyma after intravenous contrast material injection.
Incidental findings
CT imaging should be performed to evaluate specific clinical questions, but incidental findings are recorded in about 5-16% of patients scanned for unrelated reasons. It is not an acceptable practice to anticipate the possibility of incidental lesions in light of their low incidence and prospectively add additional phases to routine protocols. Unfortunately, recent surveys show that this practice is more general than anticipated, and contributes to unnecessary exposure to medical radiation in a large population of patients. Even more appalling is the fact that many of these findings could potentially be evaluated more accurately with other non-radiation imaging modalities such as MRI or ultrasound.
Although incidental management findings are not the focus of this chapter, some of these findings will require complete characterization with further CT phases such as arterial phase (specific liver tumors) or delayed images (adrenal lesions). The management of incidental findings has become controversial because they are relatively common, especially in the elderly, and more CT scans may be needed for further characterization of what is often a benign finding. In an effort to provide guidance on where incidental findings should be properly evaluated further and what appropriate imaging modalities should be, ACR publishes a white paper on the management of incidental findings detected in abdominal CT in 2010.
Conclusion
Multiphase CT testing is essential for the detection and characterization of certain clinical conditions, but should not be generalized to any patient undergoing CT from the abdomen and pelvis. A recent survey has shown that many physicians routinely perform multiphase CT for most patients in an effort to prospectively characterize the potential of detected lesions during the scan. However, multiple multiphase CT testing is an important source of medical radiation that does not contribute to patient care. Compliance with published standards such as ACR Conformity Criteria may reduce medical radiation and optimize imaging for specific clinical indications.
References
Source of the article : Wikipedia
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