这个说怎么诊断肝癌的
Imaging studies
Imaging studies play a very important role in the diagnosis of liver cancer. A good study can provide information as to the size of the tumor, the number of tumors, and whether the tumor has involved major blood vessels locally or spread outside of the liver. There are several types of studies, each having its merits and disadvantages. In practice, several studies combined often complement each other. On the other hand, a plain X-ray of the area of the liver - right, upper portion of the abdomen - is not very helpful, and therefore, is not routinely done in the diagnostic work-up of liver cancer. Further, there is no practical role for nuclear medicine scans of the liver and spleen in the workup for liver cancer. Such scans are not very sensitive and they provide no additional information beyond that provided by the other (ultrasound, CT, and MRI) scans.
Ultrasound examination is usually the first study ordered if liver cancer is suspected in a patient. The accuracy of an ultrasound depends very much on the technician and radiologist who perform the study (it is an operator dependent test). Studies from Japan and Taiwan report that ultrasound is the most sensitive imaging study for diagnosing and characterizing liver cancer. However, in these studies, highly experienced individuals performed the scans and spent up to one hour scanning each patient suspected of having liver cancer. An ultrasound has the advantages of not requiring intravenous contrast material and not involving radiation. Moreover, the price of an ultrasound is quite low as compared to the other types of scans.
Computerized axial tomography (
CT scan) is a very common study used in the U.S. for the workup of tumors in the liver. The ideal CT study is a multi-phase, spiral CT scan using oral and intravenous contrast material. Pictures are taken in three phases:
- Without intravenous contrast
- With intravenous contrast (enhanced imaging) that highlights the arterial system (arterial phase)
- When the contrast is in the venous phase
The pictures are taken at very frequent intervals (thin slices) as the body is moved through the CT scanner. Many radiologists use a specific protocol that determines how the contrast is infused in relation to how the pictures are taken. Therefore, CT is much less operator-dependent than is ultrasound. However, CT is considerably more expensive. Furthermore, CT requires the use of contrast material, which has the potential risks of an allergic reaction and adverse effects on kidney function.
There are several variations to CT scanning. For example, in a CT angiogram, which is a highly invasive (enters a part of the body) study, intravenous contrast is selectively infused through the hepatic artery (artery to the liver). The purpose is to highlight the vessels for better visualization of them by the CT scan. Also, in Japan, an oily contrast material called Lipiodol, which is selectively taken up by liver cancer cells, has been used with CT. The purpose of this approach is to improve the sensitivity of the scan. This means the goal is to increase the percentage of abnormal CT scans in patients who have liver cancer.
Magnetic resonance imaging (MRI) can provide very clear images of the body. Its advantage over CT is that MRI can provide sectional views of the body in different planes. The technology has evolved to the point that the newer MRIs can actually reconstruct images of the biliary tree (bile ducts and gallbladder) and of the arteries and veins of the liver. (The biliary tree transports bile from the liver to the duodenum, the first part of the intestine.) MRI studies can be made even more sensitive by using intravenous contrast material (for example, gadolinium).
MRI scans are expensive and there is tremendous variability in the quality of the images. The quality depends on the age of the machine and the ability of the patients to hold their breath for up to 15 to 20 seconds at a time. Furthermore, many patients, because of claustrophobia, cannot tolerate being in the enclosure of the MRI scanner. Additionally, the current open MRI scanners generally do not provide as high quality images as the closed scanners do. MRI sometimes finds lesions that are smaller than can be seen on a CT scan and can tell the radiologist more about the blood vessel (vascular) characteristics of the tumor; more importantly, there is no radiation risk, which becomes important if the screening test is to be repeated many times over a person's lifetime. A CT scan creates pictures using X-rays, while an MRI uses magnetic fields to produce the images.
Advances in ultrasound, CT, and MRI technology have almost eliminated the need for angiography. An angiography procedure involves inserting a catheter into the femoral artery (in the groin) through the aorta, and into the hepatic artery, the artery that supplies blood to the liver. Contrast material is then injected, and X-ray pictures of the arterial blood supply to the liver are taken. An angiogram of liver cancer shows a characteristic blush that is produced by newly formed abnormal small arteries that feed the tumor (neovascularization).
Another potential test used for many other cancers is a PET (positron emission tomography) scan, which involves the injection of radioactive sugar to light up actively growing cells, as in cancers. However, this is not very useful in liver cancer, as many liver cancers do not show a difference in the amount of the radioactive sugar that they take up as compared to normal liver tissue.
What, then, is the best imaging study for diagnosing liver cancer? There is no simple answer. Many factors need to be taken into consideration. For example, is the diagnosis of liver cancer known or is the scan being done for screening? What is the expertise of doctors in the patient's area? What is the quality of the different scanners at a particular facility? Are there economic considerations? Does the patient have any other conditions that need to be considered, such as claustrophobia or kidney impairment? Does the patient have any hardware, for example, a
pacemaker or metal prosthetic device? (The hardware would make doing an MRI impossible, as the magnet can shut off the pacemaker.)
If you live in Japan or Taiwan and have access to a radiologist or liver specialist (hepatologist) with expertise in ultrasound, then it may be as good as a CT scan. Ultrasound is also the most practical (easier and cheaper) for regular screening (surveillance). In North America, a multiphase spiral CT scan is probably themost accurate type of scan. However, for patients with impaired renal functionor who have access to a state-of-the-art MRI scanner, the MRI may be thediagnostic scan of choice. Finally, keep in mind that the technology of ultrasound, CT, and MRI is ever evolving with the development of better machines and the use of special contrast materials to further characterize the tumors.