Purpose, Procedure, Risks, Side-Effects, Results

Written by WebMD Editorial Contributors

• How Do CT Scans Work?
• How Are CT Scans Done?
• What Is It Used For?
• What Is a CT Scan with Contrast?
• Are There Any Risks?
• What Are the Side Effects?
• More

A computed tomography (CT or CAT) scan allows doctors to see inside your body. It uses a combination of X-rays and a computer to create pictures of your organs, bones, and other tissues. It shows more detail than a regular X-ray.

You can get a CT scan on any part of your body. The procedure doesn’t take very long, and it’s painless.

They use a narrow X-ray beam that circles around one part of your body. This provides a series of images from many different angles. A computer uses this information to create a cross-sectional picture. Like one piece in a loaf of bread, this two-dimensional (2D) scan shows a “slice” of the inside of your body.

This process is repeated to produce a number of slices. The computer stacks these scans one on top of the other to create a detailed image of your organs, bones, or blood vessels. For example, a surgeon may use this type of scan to look at all sides of a tumor to prepare for an operation.

You’d probably get a scan at a hospital or radiology clinic. Your doctor might tell you not to eat or drink for a few hours before the procedure. You may also need to wear a hospital gown and remove any metal objects, such as jewelry.

A radiology technologist will perform the CT scan. During the test, you’ll lie on a table inside a large, doughnut-shaped CT machine. As the table slowly moves through the scanner, the X-rays rotate around your body. It’s normal to hear a whirring or buzzing noise. Movement can blur the image, so you’ll be asked to stay very still. You may need to hold your breath at times.

How long the scan takes will depend on what parts of your body are being scanned. It can take anywhere from a few minutes to a half-hour. In most cases, you’ll go home the same day.

Doctors order CT scans for a long list of reasons:

• CT scans can detect bone and joint problems, like complex bone fractures and tumors.
• If you have a condition like cancer, heart disease, emphysema, or liver masses, CT scans can spot it or help doctors see any changes.
• They show internal injuries and bleeding, such as those caused by a car accident.
• They can help locate a tumor, blood clot, excess fluid, or infection.
• Doctors use them to guide treatment plans and procedures, such as biopsies, surgeries, and radiation therapy.
• Doctors can compare CT scans to find out if certain treatments are working. For example, scans of a tumor over time can show whether it’s responding to chemotherapy or radiation.

In a CT scan, dense substances like bones are easy to see. But soft tissues don’t show up as well. They may look faint in the image. To help them appear clearly, you may need a special dye called a contrast material. They block the X-rays and appear white on the scan, highlighting blood vessels, organs, or other structures.

Contrast materials are usually made of iodine or barium sulfate. You might receive these drugs in one or more of three ways:

• Injection: The drugs are injected directly into a vein. This is done to help your blood vessels, urinary tract, liver, or gallbladder stand out in the image.
• Orally: Drinking a liquid with the contrast material can enhance scans of your digestive tract, the pathway of food through your body.
• Enema: If your intestines are being scanned, the contrast material can be inserted in your rectum.

After the CT scan, you’ll need to drink plenty of fluids to help your kidneys remove the contrast material from your body.

CT scans use X-rays, which produce ionizing radiation. Research shows that this kind of radiation may damage your DNA and lead to cancer. But the risk is still very small — your chances of developing a fatal cancer because of a CT scan are about 1 in 2,000.

But radiation’s effect adds up over your lifetime. So your risk increases with every CT scan you get. Talk to your doctor about the procedure’s potential dangers and benefits, and ask why the CT scan is necessary.

Ionizing radiation may be more harmful in children. That’s because they’re still growing. They also have more years to get exposed to radiation. Before the procedure, you may want to ask the doctor or technician if the CT machine’s settings have been adjusted for a child.

Tell your physician if you’re pregnant. If you need imaging for your stomach area, your doctor may recommend an exam that doesn’t use radiation, such as an ultrasound.

Some people are allergic to the contrast materials. Most of the time, the reaction is mild. It can lead to itchiness or a rash. In very few cases, the dye may trigger a life-threatening reaction. For this reason, your health care provider may want to monitor you for a short period after your CT scan. Tell your doctor about any allergies you have to medications, seafood, or iodine.

Your doctor should know, too, if you have diabetes and are taking the drug metformin. They’ll let you know if you should stop taking your medication before or after your procedure.

Although it’s rare, contrast materials can lead to kidney problems. Let your doctor know if you have any kidney issues before the CT scan.

Next In How to Diagnose Cancer

Next Biopsy

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Purpose, Procedure, Risks, Side-Effects, Results

Written by WebMD Editorial Contributors

• How Do CT Scans Work?
• How Are CT Scans Done?
• What Is It Used For?
• What Is a CT Scan with Contrast?
• Are There Any Risks?
• What Are the Side Effects?
• More

A computed tomography (CT or CAT) scan allows doctors to see inside your body. It uses a combination of X-rays and a computer to create pictures of your organs, bones, and other tissues. It shows more detail than a regular X-ray.

You can get a CT scan on any part of your body. The procedure doesn’t take very long, and it’s painless.

They use a narrow X-ray beam that circles around one part of your body. This provides a series of images from many different angles. A computer uses this information to create a cross-sectional picture. Like one piece in a loaf of bread, this two-dimensional (2D) scan shows a “slice” of the inside of your body.

This process is repeated to produce a number of slices. The computer stacks these scans one on top of the other to create a detailed image of your organs, bones, or blood vessels. For example, a surgeon may use this type of scan to look at all sides of a tumor to prepare for an operation.

You’d probably get a scan at a hospital or radiology clinic. Your doctor might tell you not to eat or drink for a few hours before the procedure. You may also need to wear a hospital gown and remove any metal objects, such as jewelry.

A radiology technologist will perform the CT scan. During the test, you’ll lie on a table inside a large, doughnut-shaped CT machine. As the table slowly moves through the scanner, the X-rays rotate around your body. It’s normal to hear a whirring or buzzing noise. Movement can blur the image, so you’ll be asked to stay very still. You may need to hold your breath at times.

How long the scan takes will depend on what parts of your body are being scanned. It can take anywhere from a few minutes to a half-hour. In most cases, you’ll go home the same day.

Doctors order CT scans for a long list of reasons:

• CT scans can detect bone and joint problems, like complex bone fractures and tumors.
• If you have a condition like cancer, heart disease, emphysema, or liver masses, CT scans can spot it or help doctors see any changes.
• They show internal injuries and bleeding, such as those caused by a car accident.
• They can help locate a tumor, blood clot, excess fluid, or infection.
• Doctors use them to guide treatment plans and procedures, such as biopsies, surgeries, and radiation therapy.
• Doctors can compare CT scans to find out if certain treatments are working. For example, scans of a tumor over time can show whether it’s responding to chemotherapy or radiation.

In a CT scan, dense substances like bones are easy to see. But soft tissues don’t show up as well. They may look faint in the image. To help them appear clearly, you may need a special dye called a contrast material. They block the X-rays and appear white on the scan, highlighting blood vessels, organs, or other structures.

Contrast materials are usually made of iodine or barium sulfate. You might receive these drugs in one or more of three ways:

• Injection: The drugs are injected directly into a vein. This is done to help your blood vessels, urinary tract, liver, or gallbladder stand out in the image.
• Orally: Drinking a liquid with the contrast material can enhance scans of your digestive tract, the pathway of food through your body.
• Enema: If your intestines are being scanned, the contrast material can be inserted in your rectum.

After the CT scan, you’ll need to drink plenty of fluids to help your kidneys remove the contrast material from your body.

CT scans use X-rays, which produce ionizing radiation. Research shows that this kind of radiation may damage your DNA and lead to cancer. But the risk is still very small — your chances of developing a fatal cancer because of a CT scan are about 1 in 2,000.

But radiation’s effect adds up over your lifetime. So your risk increases with every CT scan you get. Talk to your doctor about the procedure’s potential dangers and benefits, and ask why the CT scan is necessary.

Ionizing radiation may be more harmful in children. That’s because they’re still growing. They also have more years to get exposed to radiation. Before the procedure, you may want to ask the doctor or technician if the CT machine’s settings have been adjusted for a child.

Tell your physician if you’re pregnant. If you need imaging for your stomach area, your doctor may recommend an exam that doesn’t use radiation, such as an ultrasound.

Some people are allergic to the contrast materials. Most of the time, the reaction is mild. It can lead to itchiness or a rash. In very few cases, the dye may trigger a life-threatening reaction. For this reason, your health care provider may want to monitor you for a short period after your CT scan. Tell your doctor about any allergies you have to medications, seafood, or iodine.

Your doctor should know, too, if you have diabetes and are taking the drug metformin. They’ll let you know if you should stop taking your medication before or after your procedure.

Although it’s rare, contrast materials can lead to kidney problems. Let your doctor know if you have any kidney issues before the CT scan.

Next In How to Diagnose Cancer

Next Biopsy

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Chipping of dogs and cats

So, why should a cat or dog be microchipped? The most important reason is that the microchip greatly increases the chance that you will find your pet if it is lost or stolen. In addition, many countries do not accept animals without a microchip.

Veterinary center “Sozvezdie” performs microchipping of pets around the clock. This is a routine procedure that is safe and does not take much time.

What is a microchip?

A microchip is a small electronic chip enclosed in a glass cylinder about the size of a grain of rice. The microchip itself does not have a battery, it is activated using a scanner when the latter is brought to the location of the chip. Scanner radio waves activate the chip. The chip transmits an identification number to the scanner, which is displayed on its screen.

How is a microchip implanted in an animal? Is it painful? Need surgery or pain relief?

The chip is inserted under the skin using a special hypodermic needle. Chipping is no more painful to a cat, dog, or other animal than a regular subcutaneous injection, although the needle is slightly larger than those used to administer liquids.

No surgery or anesthesia is required for chipping – the microchip can be implanted during a routine visit to the veterinary clinic.

If your pet is already under anesthesia for an operation such as neutering or spaying, the microchip can be implanted while he is still under anesthesia.

What information is contained in the microchip? Is there a tracking device in it? Will it store my pet’s medical information?

Microchips currently used in cats and dogs only contain identification numbers. No, the microchip cannot track your pet if it gets lost.

Although the microchip itself does not contain your pet’s medical information, some databases allow you to store certain information, such as chronic illnesses or needed treatments.

Some microchips used in research laboratories and for chipping livestock and horses also transmit information about the animal’s body temperature.

What is meant by “microchip frequency”?

The microchip frequency actually refers to the frequency of the radio waves transmitted by the scanner that activates the microchip and reads information from it. Examples of microchip frequencies: 125 kHz, 128 kHz, and 134.2 kHz.

I heard about something called “ISO standard”, what does that mean?

The International Organization for Standardization, or ISO, has endorsed and recommended a global standard for microchips. The global standard is intended to create an identification system that is used throughout the world.

For example, if a dog was implanted with an ISO microchip in Russia, and then it ends up in Europe and gets lost, then using a standard ISO scanner in Europe, a specialist will be able to scan the dog’s microchip. The standard ISO frequency is 134.2 kHz.

If a non-ISO microchip has been implanted in a dog and the ISO scanner used is not universal, the dog’s microchip may not be detected or scanned.

What are universal (wide range) scanners? How are they different from ordinary ones?

Conventional scanners only detect chips at 134.2 kHz (ISO standard) and do not detect chips at 125 kHz or 128 kHz (non-ISO standard). Universal scanners, also called wide-range scanners, can detect microchips operating at any frequency.

The main advantage of universal scanners is the better ability to detect and read the microchip, regardless of its frequency.

How does a microchip help return an animal to its owner?

When an animal is found and taken to a shelter or veterinary clinic, one of the first things that is done is to scan the animal for a microchip.

If a microchip is detected, and if the information under the identification number is correctly entered into the database, then the owner of the animal is easily and quickly located.

How quickly do chipped cats and dogs return to their owners in case of loss of an animal?

A study of more than 7,800 stray animals from shelters showed that dogs without microchips returned to their owners in 21.9% of cases, dogs with microchips returned to their owners in 52.2% of cases.

Cats without microchips were returned to their owners only in 1.8% of cases, cats with microchips were returned to their owners in 38.5% of cases.

For chipped animals that have not found owners, in most cases, the owner information in the microchip registry database was filled in incorrectly or was missing – so do not forget to register and update your data in the database as needed.

Does the microchip replace identification tags (address tag)?

No. Microchips are great for permanent identification of dogs and cats that is secure from damage, but nothing beats a collar with an ID tag.

Which countries require animal microchipping?

You will definitely need to have your pet microchipped if you are planning a trip to the EU countries or Kazakhstan, as well as a number of acute countries.

If you are planning to travel with a pet abroad, be sure to check the country-specific animal import requirements. Even within the EU, the requirements of different countries may vary.

Is microchipping of animals mandatory in Russia?

No, today chipping is not mandatory in Russia, unlike mandatory vaccination against rabies.

Why can’t I just buy a microchip and implant it myself?

Implantation looks quite simple, not more complicated than a conventional injection, right? Yes and no. Although it looks like a simple injection, it is very important that the microchip is implanted properly.

Using too much force, plunging the needle too deep, or inserting the chip in the wrong place can not only make it harder to find and read the chip in the future, but can also cause health and even life-threatening problems for the pet.

Microchips should be implanted by a veterinarian because veterinarians know where microchips should be placed, how to properly implant them, and know how to recognize signs of chip problems and what to do about it.

After the microchip has been implanted, what should I do? Is maintenance needed?

No, the microchips themselves do not require maintenance, but you must keep your contact information in the registration database up to date (primarily your contact phone number).

If you notice any abnormalities at the site where the microchip was implanted, such as bleeding or induration, contact your veterinarian.

Why are microchips sometimes not found?

As with almost any device, there is no 100% fault tolerance guarantee. It is extremely rare for microchips to stop functioning and cannot be detected using a scanner.

Extremely rare, but there are problems with the scanner. A human factor cannot be ruled out: for example, incorrect scanning technique or incomplete scanning of an animal.

Some of the animal-related factors that can make the microarray difficult to detect include the following: Animals that will not stand still during scanning; the presence of long, tangled hair at or near the microchip implantation site; a metal collar (or a collar with a lot of metal). All this can affect the scanning and detection of the microchip.

My pet has two microchips with different frequencies. Do I need to remove one of them? Will they interfere with each other? What microchip will be detected by the scanner?

No, nothing needs to be deleted. The microchips will not interfere with each other. Which microchip that will be detected by the scanner depends only on the scanner – if the scanner is universal, then both chips will probably be detected.

If it is a scanner that reads only one frequency, it will only detect the microchip at that particular frequency and will not detect or read another chip.

If you know your pet has more than one microchip, make sure the database is updated for each microchip. Finders of your pet usually don’t assume that a found pet has more than one microchip (because it’s very rare) and will try to find the owner based on the first microchip they find.

My pet has a non-ISO chip and I want to have an ISO chip implanted. I can do it?

Of course you can. Both chips will work normally. If your pet is scanned with a scanner that only reads 125 kHz chips, only a 125 kHz chip will be detected. If your pet is being scanned by a universal scanner, one or both chips may be detected (see above for more information).

I want to travel to a country that requires cats and dogs to have an ISO chip, and my pet does not have a chip of this standard or does not have a microchip at all. What do I need to do?

Your pet must have an ISO microchip implanted before they are allowed into this country. But that’s not the only thing you need to know: countries differ in their rules for bringing animals into the country, including different provisions on required vaccinations and quarantine periods after an animal is brought into the country.

If you know the rules for bringing a pet into a particular country in advance and prepare, your pet’s move will go smoothly.

Is there a single animal microchip database that records information and makes it available to shelters and veterinary clinics in case my pet is lost or stolen?

Currently there is no unified database. In Russia for registration of microchips; each manufacturer maintains its own database. Since ISO standards for identification codes have not been adopted in Russia, microchips must be registered in a special manufacturer’s database.

Fortunately, scanners display the name of the microchip manufacturer when they are read. Thus, the possibility that the animal cannot be identified due to the fact that it is not clear in which database to look for data is excluded.

In Russia, the most popular database of dog and cat microchips is the animal-id.ru website (we enter information into it when chipping your animal), information from it is transferred to international chip databases.

What are the problems with microchips in dogs and cats? How common are they?

The British Veterinary Medicine Association (BSAVA) maintains a database of adverse reactions to microarrays. According to statistics, the probability of adverse reactions after chipping dogs, cats and other animals is less than 0.0001% percent. Of these reactions, the most common is the migration of the microchip from its original implantation site.

Other problems such as microchip failure, hair loss at the insertion site, infections, swelling and neoplasms have been reported in much lower numbers.

I heard that microchips cause cancer. Is it so?

There have been reports that implanted mice and rats developed cancer. However, most of these mice and rats have been used for cancer research, and the strains of rats and mice used in cancer research are known to be more prone to developing cancer.

Question about the pros and cons of chipping. It is clear that a chipped animal has a greater chance of returning home. But what if the veterinary clinic or shelter can’t read the chip?

The benefits of microchipping animals definitely outweigh the risks. While we cannot guarantee that a shelter or veterinary clinic will be able to read any microchip anyway, the risk that a chip will not be read is very low and is getting lower every year.

Animal shelters and veterinary clinics are aware of the nuances of finding microchips in found animals and are taking additional steps to find a microchip. Universal scanners are becoming more available, which solves the problem of finding different microchips.

With the latest advances in veterinary oncology for cats and dogs, owners and their pets have more options and hope than ever before when it comes to treating cancer in cats and dogs.

Specialized scientific and practical publications for veterinarians and students of veterinary universities.

Authors: Azarova M. S., Gerasimov A. S., Ivan Fillmore Veterinary Clinic, St. Petersburg.

Introduction

Portosystemic shunts are anomalies of the abdominal cavity vessels, in which part of the blood or all of the blood from the portal vein system, bypassing the liver, enters the main bloodstream.

In a healthy animal, the portal vein drains blood from the stomach, small and large intestine (excluding the caudal rectum), and spleen to the liver (Figure 1). In the liver, this blood, containing protein breakdown products, undergoes detoxification.

In an animal with a portosystemic shunt, blood from the portal vein is shed into the common vein without being detoxified by the liver. The breakdown products of proteins and nutrients that enter the general bloodstream from the gastrointestinal tract determine the development of the clinical picture.

Photo 1. Normal venous blood flow.

Photo 2. The venous duct in the fetus.

HV – unpaired vein , CVV – caudal vena cava , PV – portal vein , PV – umbilical vein .

Clinical signs

Common clinical manifestations include weight loss, stunting, poor coat quality, low body temperature, salivation, and vomiting.

In addition, hepatoencephalopathy can develop, affecting almost all parts of the brain, which is manifested by lethargy, depression, lack of coordination, convulsive seizures, and in severe cases, coma can develop. The severity of hepatoencephalopathy depends on the protein content of the food. When switching to a low-protein diet, the condition of patients improves.

Classification

Portosystemic shunts can be congenital or acquired. Congenital shunts are considered as embryonic anastomoses preserved after birth (photo 2), which are the norm for the fetus at one or another stage of intrauterine development.

Acquired shunts are the body’s response to portal hypertension. An increase in pressure in the portal vein can develop due to cirrhosis, fibrosis and other liver diseases, leading to a change in the vascular bed of the parenchyma. It is assumed that the shunt in this case can develop from an anastomosis normal for the embryo, which existed in the fetus, but became empty before or after birth.

If the vessel shunting the hepatic blood flow is located inside the liver, it is called intrahepatic (photo 3), if outside the liver – extrahepatic (photo 4).

Shunts can be single, double or multiple.

In addition to the open ductus venosus and the portocaval shunt, that is, the anastomosis between the portal vein and the caudal vena cava, there are other topological variants of shunts. Shunts may originate from the portal, splenic, or gastric veins, and drain blood into the caudal vena cava, azygos, or diaphragmatic vein.

HV – unpaired vein , CVV – caudal vena cava , PV – portal vein , PV – umbilical vein .

Breed predispositions

Extrahepatic portosystemic shunts are more common in purebred small breed dogs: Chihuahua, Lhasa Apso, Shih Tzu, Maltese, various small terriers, miniature schnauzers, and dachshunds. Intrahepatic shunts usually affect large and medium breed dogs: Australian Cattle Dogs, Irish Wolfhounds, Labradors, German Shepherds.
Photo 3. Intrahepatic porto-caval shunt (arrow).

Photo 4. Extrahepatic shunt (arrow) between the caudal vena cava and the azygos vein.

Among cats, portosystemic shunts are most common in the Himalayan, Domestic Shorthair, Persian, and Siamese breeds. As a rule, extrahepatic shunts are detected in cats.

Laboratory research

Biochemical blood test:

• Hypoalbuminemia and reduced blood levels of total protein.
• Low concentration of urea nitrogen in the blood.
• Low cholesterol and blood glucose levels.
• Increased concentration of liver enzymes.
• Increase in blood ammonia between meals.
• Sharp increase in serum bile acids (test before and after feeding).

CBC:

• 72% of dogs show microcytosis with or without associated anemia.
• Leukocytosis may occur.
• Urinalysis:
• Decreased density of urine.
• There may be signs of cystitis.
• The presence of urate in the urine of a young animal is an indication for further investigation.

Histological examination of the liver tissue:

• Allows you to identify the causes that led to the formation of acquired shunts, microvascular dysplasia and other pathologies that are not always detectable by other methods.

Visual diagnostics

Clinical signs and laboratory findings suggest a shunt. Visual diagnostic methods help to confirm the diagnosis and evaluate the topology of the vessels.

Ultrasound

The liver is small. The veins of the liver are very small or completely indistinguishable. Ammonium urate crystals are found in the kidneys and bladder.

Intrahepatic shunts are easier to visualize (Figure 5), extrahepatic shunts are more difficult. Doppler ultrasound can detect turbulent flow in the vena cava and portal vein, which usually occurs in the area of ​​the shunt.

The likelihood of detecting portosystemic shunts in animals by ultrasound scanning varies widely and is largely determined by the level of training and experience of the specialist conducting the study.

CVV – caudal vena cava , BB – portal vein , W – shunt .

X-ray examinations
On survey radiographs of the abdominal cavity, a decrease in the size of the shadow of the liver is revealed. To visualize the boundaries of the stomach, an aqueous suspension of barium sulfate is drunk to the animal before radiography. On plain radiographs, shadows of radiopaque stones in the kidneys and bladder can be detected. Ammonium urate crystals are not radiopaque, but it is not uncommon for portosystemic shunts to form stones of a more complex composition that are radiopaque.

Angiography is used to visualize blood vessels – the introduction of a radiopaque preparation into the blood vessels. Angiography can be non-selective (general) and selective (selective). In non-selective angiography, a radiopaque agent is injected through a peripheral vessel into the general bloodstream. With selective – a radiopaque drug is injected into the vessel of interest.

Photo 5. Intrahepatic shunt on ultrasound.

Photo 6. Portography radiograph with introduction.

radiopaque substance into the mesenteric vein is normal.
Selective contrasting of the portal vein is called portography. There are several ways to inject a contrast agent into the portal vein.

Mesenteric vein portography is currently the “gold standard” in the diagnosis of portosystemic shunts. This is an invasive method. The animal under general anesthesia is undergoing a laparotomy, the mesenteric vein is catheterized, and the line from the catheter is removed outside the abdominal cavity. Next, a radiopaque preparation is injected through the highway, which enters the portal vein through the mesenteric vein, and a series of radiographs is immediately taken (photo 6). This method allows visualization of the portal vein, shunt (Figure 7) and liver vessels.

BB – portal vein .

CVV – caudal vena cava , BB – portal vein .

Portography with the introduction of a radiopaque agent into the parenchyma of the spleen is a less invasive method. Spleen puncture is performed without laparotomy, through the abdominal wall under ultrasound control. A radiopaque preparation is injected into the parenchyma of the spleen, which enters the splenic vein, and from it into the portal vein. A series of radiographs is taken. This route of introduction allows visualization of those shunts that originate from the splenic vein and from the portal vein after the splenic vein flows into it.

Portography with the introduction of a radiopaque agent into the cranial mesenteric artery does not require laparotomy, but requires a catheterization of the femoral artery, through which the catheter under radiographic control advances along the abdominal aorta to the cranial mesenteric artery. A contrast agent is injected, which travels through the mesenteric artery into the intestinal capillaries, and from there into the mesenteric veins and portal vein.

Non-selective angiography of the portal vein is not applicable for radiography because, due to the large number of vessels closely located in the abdominal cavity and the contrasting of the intestinal loops and parenchymal organs injected with the preparation, it is impossible to interpret the image obtained.

Scintigraphy

The method of functional imaging, which consists in the fact that the animal under study is injected (rectally or intrasplenicly) with a radioactive drug that enters the portal vein, and from there into the liver (in a healthy animal) or venous blood flow (in the presence of a shunt). After the introduction of the drug, the timing of its accumulation in the liver and heart is monitored. In healthy animals, the liver accumulates the drug faster than the heart.
Photo 7. Portography radiograph with the introduction of a radiopaque agent into the mesenteric vein – portocaval shunt.

Photo 8. CT with the introduction of a radiopaque agent into a peripheral vein – a porto-caval shunt (3D reconstruction).

The method has become widespread in the United States, since there are a large number of scientific centers with equipment for scintigraphy. The drug contains an isotope of technetium with a half-life of about 6 hours. It is obtained in isotope generators immediately before use. Gamma cameras are used to record radiation.

The study is non-invasive (in the case of rectal administration of the drug), but it only allows you to estimate how much of the blood coming from the intestines bypasses the liver. That is, you can confirm the presence of a shunt, but not visualize it.

CT angiography

CT angiography (CTA) is a method of obtaining images of blood vessels using a computed tomography scanner. The advantage of CT angiography is that this method makes it possible to visualize the vessels of the abdominal cavity, including the portal vein, without resorting to selective contrast enhancement. Computed tomography, unlike radiography, provides the ability to work with images of sections and three-dimensional models, and for it the complex vascular anatomy of the abdominal cavity is not an obstacle (photo 8).

In non-selective CT angiography, a radiopaque drug is injected into a peripheral vein of the thoracic limb, from where it enters the heart, passes through the pulmonary circulation, returns to the heart and enters the aorta. From the descending aorta, blood with a contrast agent enters the vessels of the spleen and intestines, and from there into the portal vein. The passage of a contrast agent through the vessels is a dynamic process. Usually, several series of scans are made in different phases of the passage of contrast.

For good visualization of the shunt, it is necessary that the scanning of the area of ​​interest occurs while the maximum amount of contrast agent is in the portal venous system. The time of appearance of the contrast agent in the portal vein depends on the blood flow velocity, which can vary greatly in different animals. In practice, two methods are used to obtain high-quality images: measuring the time of appearance of contrast in the portal vein according to a preliminary series and a bolus tracker.

A – abdominal aorta , BB – part of the portal vein from the intestine to the shunt , CVV – caudal vena cava , III – shunt , CB – splenic vein 901 56 .

To measure the time of appearance of contrast in the portal vein, a small amount of contrast agent is injected before the preliminary series of scans; portal vein. Scanning of this slice lasts 1-2 minutes with a frequency of 1 time in 0.5-2 seconds. The obtained images determine the time interval between the intravenous administration of the drug and its appearance in the portal vein. Based on this, a series is planned and carried out with the introduction of a full dose of a contrast agent.

With the bolus tracker technique, no pre-series is required, the full dose of the drug is administered immediately, and the study protocol used consists of a tracking series and helical scan series. During the tracking series, the same section is scanned every 1-2 seconds, which immediately automatically determines the X-ray density of blood in the lumen of the selected vessel. As soon as the density exceeds the specified threshold (that is, a sufficient amount of radiopaque agent appears in the vessel), the helical scanning of the zone of interest begins. Subsequent series begin after a specified time after the start of the first series. As a rule, several series of scans are performed in different vascular phases. Large arteries and veins of the abdominal cavity are visualized.

CT angiography allows not only detecting a shunt, but also comprehensively describing its topography: examining between which vessels blood is shed, describing the localization of the shunt, assessing its size, identifying the presence of multiple shunts, assessing liver perfusion.

MRI angiography

Magnetic resonance angiography (MRA) is a method of obtaining images of blood vessels using a magnetic resonance tomograph. The method allows to evaluate both anatomical and functional features of blood flow. MRA is based on the difference between the signal of moving tissue (blood) and surrounding fixed tissues, which allows you to obtain images of blood vessels without the use of any radiopaque agents. To obtain a clearer image during MR angiography, radiopaque agents (based on gadolinium salts) injected into a peripheral vein can be used.

Treatment and prognosis

Conservative treatment is aimed at reducing the amount of toxins coming from the stomach and intestines into the portal vein. It consists in the selection of food, enterosorbents and the appointment of procedures aimed at restoring the water, glucose and electrolyte balance of the body. It also suggests the prevention of hepatic encephalopathy.

Surgical treatment consists in partial or complete, simultaneous or gradual ligation of the pathological vessel. For extrahepatic shunts, ameroid constrictors and cellophane ligatures are used; for intrahepatic shunts, embolization with intravascular coils is used.

Literature:

1.​ A. Gough, A. Thomas. Breed predisposition to diseases in dogs and cats. M., “Aquarium”, 2005.

2. K. Pratchke. Portosystemic shunts in dogs: a review of diagnostic and treatment approaches. Veterinary Focus, 2010, 20.3

3. J. D. Bonagura, R. Kirk. Kirk’s Modern Course in Veterinary Medicine. M., Aquarium, 2005.

4.​ D. E. Thrall et al. Textbook of Veterinary Diagnostic Radiology, Sixth Edition. Elsevier, 2013.

5. T. Schwarz, J. Saunders. Veterinary Computed Tomography. Wiley-Blackwell, 2011.

6. A. Bruehschwein et al. Contrast-enhanced magnetic resonance angiography for diagnosis of portosystemic shunts in 10 dogs. Vet Radiol Ultrasound 2010, 51.

7. N. C. Nelson, L. L. Nelson. Anatomy of extrahepatic portosystemic shunts in dogs as determined by computed tomography angiography. Vet Radiol Ultrasound 2011, 52.

8. S. E. Kim et al. Comparison of computed tomographic angiography and ultrasonography for the detection and characterization of portosystemic shunts in dogs.