When a sound wave strikes an object, it bounces back or echoes. By measuring these echo waves, it is possible to determine how far away the object is as well as its size, shape, and consistency. This includes whether the object is solid or filled with fluid.
Doctors use ultrasound to detect changes in the appearance of organs, tissues, and vessels and to detect abnormal masses, such as tumors. In an ultrasound exam, a transducer both sends the sound waves and records the echoing returning waves. When the transducer is pressed against the skin, it sends small pulses of inaudible, high-frequency sound waves into the body. As the sound waves bounce off internal organs, fluids and tissues, the sensitive receiver in the transducer records tiny changes in the sound's pitch and direction.
A computer instantly measures these signature waves and displays them as real-time pictures on a monitor. The technologist typically captures one or more frames of the moving pictures as still images. They may also save short video loops of the images.
Doppler ultrasound, a special ultrasound technique, measures the direction and speed of blood cells as they move through vessels. The movement of blood cells causes a change in pitch of the reflected sound waves called the Doppler effect. A computer collects and processes the sounds and creates graphs or color pictures that represent the flow of blood through the blood vessels.
For most ultrasound exams, you will lie face-up on an exam table that can be tilted or moved. Patients may turn to either side to improve the quality of the images. The radiologist a doctor specifically trained to supervise and interpret radiology exams or sonographer will position you on the exam table. They will apply a water-based gel to the area of the body under examination.
The gel will help the transducer make secure contact with the body. It also eliminates air pockets between the transducer and the skin that can block the sound waves from passing into your body.
The sonographer places the transducer on the body and moves it back and forth over the area of interest until it captures the desired images.
There is usually no discomfort from pressure as they press the transducer against the area being examined. However, if the area is tender, you may feel pressure or minor pain from the transducer. Once the imaging is complete, the technologist will wipe off the clear ultrasound gel from your skin. Any portions that remain will dry quickly. The ultrasound gel does not usually stain or discolor clothing.
If the doctor performs a Doppler ultrasound exam, you may hear pulse-like sounds that change in pitch as they monitor and measure the blood flow. When the exam is complete, the technologist may ask you to dress and wait while they review the ultrasound images.
A radiologist, a doctor trained to supervise and interpret radiology exams, will analyze the images. The radiologist will send a signed report to the doctor who requested the exam.
Your doctor will then share the results with you. In some cases, the radiologist may discuss results with you after the exam. You may need a follow-up exam. If so, your doctor will explain why. Sometimes a follow-up exam further evaluates a potential issue with more views or a special imaging technique. It may also see if there has been any change in an issue over time. Follow-up exams are often the best way to see if treatment is working or if a problem needs attention. Ultrasound waves are disrupted by air or gas.
Therefore, ultrasound is not an ideal imaging technique for the air-filled bowel or organs obscured by the bowel. Ultrasound is not as useful for imaging air-filled lungs, but it may be used to detect fluid around or within the lungs.
Similarly, ultrasound cannot penetrate bone, but may be used for imaging bone fractures or for infection surrounding a bone. Large patients are more difficult to image by ultrasound because greater amounts of tissue weaken the sound waves as they pass deeper into the body and need to return to the transducer for analysis.
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Outside links: For the convenience of our users, RadiologyInfo. Toggle navigation. What is Ultrasound Imaging of the Abdomen? What are some common uses of the procedure? How should I prepare? What does the equipment look like How does the procedure work? How is the procedure performed? What will I experience during and after the procedure? Who interprets the results and how do I get them? What are the benefits vs.
What are the limitations of Abdominal Ultrasound Imaging? A Doppler ultrasound study may be part of an abdominal ultrasound examination. Abdominal ultrasound imaging is performed to evaluate the: kidneys liver gallbladder bile ducts pancreas spleen abdominal aorta and other blood vessels of the abdomen Ultrasound is used to help diagnose a variety of conditions, such as: abdominal pain or distention enlargement abnormal liver function enlarged abdominal organ kidney stones gallstones an abdominal aortic aneurysm AAA Additionally, ultrasound may be used to provide guidance for biopsies.
The CT examination illustrates that the pancreas is not entirely in the horizontal plane and that the pancreatic head has a caudal orientation from the corpus. The echo reflection pattern will become more echogenic with age. The abdominal aorta is located centrally in the abdomen fig. It can be difficult to image it effectively, particularly with significant obesity and extensive intestinal gas.
Adequate compression is necessary. The small intestines can never be imaged in their entirety by ultrasound. However, ultrasound may be very helpful in common intestinal pathologies.
The intestinal wall appearance changes markedly from the small intestine Kerkring folds to the colon haustrations.
Intestinal gas is a limiting factor in reliable evaluation of the intestinal wall fig. In some cases, intestinal compression may improve imaging. When compression does not help, evaluation of the intestinal anterior wall will have to suffice. For the purpose of evaluating the duodenum or pylorus, it may be very helpful to have the patient drink a few cups of water prior to or during the examination.
A fluid-filled lumen creates the ideal acoustic window for evaluation of the entire intestinal wall. We are frequently asked to assess patients with abdominal pain for appendicitis.
The appendix is in the right lower quadrant. The appendix is compressible and normally has a diameter of under 7 mm fig. Figure 23b. A healthy appendix is compressible. Compressibility can be evaluated effectively by imaging the appendix in the transversal plane.
Figure 23c. Healthy appendix. The appendix lies close to the surface and has a winding course, originating at the medial side of the cecum. The air-filled cecum acoustic shadowing! Each radiologist will have his or her personal preferences for imaging abdominal organs. As a general rule, each organ and abnormality is imaged in two directions; in most cases the transversal and sagittal directions.
Fatty liver degeneration will make the liver parenchyma echogenic as compared to the kidney parenchyma fig. This is termed liver steatosis. Causes of steatosis include alcohol abuse, diabetes and obesity. Liver steatosis; the liver parenchyma is highly echogenic vs the right kidney cortex. In advanced stages, liver volume will decrease and the liver parenchyma will have a coarse-grain echo reflection pattern fig.
Multiple focal abnormalities may be found in the liver. Another frequent finding in the liver is a liver cyst. A cyst is a benign, thin-walled fluid vesicle. Cysts have anechogenic black content. In order to distinguish cysts from anechogenic solid lesions, two artifacts are used: posterior wall enhancement and increased sound transmission fig.
For additional information on ultrasound artifacts, see the Ultrasound Technique course. Small liver cysts are usually asymptomatic and aspecific. Large cysts can in some cases exert a mass effect on the surrounding structures and thereby induce symptoms. Another frequent benign abnormality in the liver is the hemangioma. Most hemangiomas are asymptomatic, sharply delineated echogenic small lesions fig.
Perfusion in hemangiomas is slow, frequently preventing the use of color Doppler to demonstrate flow. In some cases, hemangiomas have an aspecific echo reflection pattern, making them indistinguishable from other liver abnormalities e. A hemangioma in the liver parenchyma. The hemangioma has no color Doppler signal. Other benign liver lesions include granuloma, focal nodular hyperplasia FNH and adenoma; they will be discussed in more detail in a subsequent course.
Metastases are the most common malignant liver abnormalities. In most cases, these patients have an oncologic history. Depending on the primary tumor, metastases may have either an anechogenic or echogenic reflection pattern fig. Usually they are mostly anechogenic. Metastases are frequently solid and vaguely delineated; flow cannot be demonstrated using color Doppler. Multiple liver metastases. Note also increased echogenicity of the liver parenchyma as compared to the cortex of the right kidney , consistent with steatosis.
In patients with liver cirrhosis, hepatocellular carcinoma HCC is a common malignant abnormality. The echo reflection pattern varies from anechogenic to echogenic or a mix. Flow may be imaged using color Doppler in HCC, making it distinguishable from a metastasis or hemangioma. When the gallbladder contains bile stones, they can be imaged effectively using ultrasound.
In order to evaluate bile stone mobility, you can ask the patient to lie on his or her left side or stand if possible. The bile stones will move to the bottom with gravity. An immobile echogenic nodular lesion in close correlation with the gallbladder wall without acoustic shadowing is termed a gallbladder polyp, frequently consisting of cholesterol fig.
The polyps will not move with gravity. It causes biliary outflow obstruction, putting pressure on the gallbladder. When the bile stone has been lodged chronically with associated bile stone colic, the gallbladder wall will thicken and have a layered aspect: the wall has become edematous fig. A lodged stone with acoustic shadowing in the gallbladder neck with localized wall thickening. The choledochal duct can be evaluated by localizing the portal vein in the liver hilum; the choledochal duct is ventral of the portal vein.
A stone in the choledochal duct may cause obstruction and dilatation. In the event of bile duct obstruction, the intrahepatic bile ducts will become visible fig.
This is termed the tram track sign fig. Figure 35a. Dilated peripheral intrahepatic bile ducts with the tram track sign. Color Doppler reveals flow in the portal branches as opposed to the bile ducts. Figure 35b. Markedly dilated central bile ducts. Urinary outflow obstruction will cause the pyelocaliceal system to dilate: this is termed hydronephrosis fig. Hydronephrosis may have several causes, e.
Like bile stones, kidney stones cause acoustic shadowing fig. Very small renal concrements of a few millimeters may be missed in ultrasound examination as the acoustic shadowing is invisible. The gold standard to demonstrate or exclude nephrolithiasis is an abdominal CT examination without contrast. Left kidney in the sagittal plane. A large concrement in the pyelum with proximal dilatation of the renal collecting system.
One of the most common abnormalities in the kidneys are cysts fluid-filled sacs. Cysts are generally asymptomatic. An uncomplicated kidney cyst with posterior wall enhancement and increased sound transmission. Cysts may vary markedly in size. It is important to carefully evaluate the cyst wall and exclude any solid components. In the event of solid components or multiple septations, additional characterization using abdominal CT is indicated fig.
One of the most common malignant lesions in the kidney is renal cell carcinoma RCC. This is usually a solid mass with a heterogeneous reflection pattern and vascularization fig. Spherical heterogeneous mass in the right kidney lower pole PA: renal cell carcinoma. The bladder must be filled for adequate bladder wall evaluation.
The bladder usually has anechogenic content without wall irregularities. In the event of trauma, blood clots may add mobile echogenic content to the bladder fig. Wall irregularities may signify a bladder tumor fig. In practice, it is not always clear whether tissue is solid; cystoscopy is indicated for additional evaluation. The spleen usually has a craniocaudal dimension of 12 cm and a triangular shape. The spleen may increase in size in the event of e. This will give the spleen a plump aspect with rounded rims.
Patient with liver cirrhosis and portal hypertension with splenomegaly craniocaudal length 18 cm. Note also collateral vessel formation in the splenic hilum. Cysts and hemangiomas may also develop in the spleen. The most common malignant abnormality is lymphoma. Pancreatic imaging may be complicated by air content in the stomach or interfering intestinal gas in the transversal colon.
When asked to confirm or exclude pancreatitis, the origin of symptoms and the ability of ultrasound to demonstrate abnormalities should be taken into account. Despite abnormal blood chemistry, there will be no or few abnormalities on ultrasound over the first days.
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