CT Scans for Staging Mesothelioma Tumors

CT scans can help doctors determine the stage of a mesothelioma tumor by revealing whether or not it has spread to nearby tissues, the lymph nodes or to distant organs. A relatively new technique known as CT perfusion is especially effective at determining whether or not cancer cells have begun to spread throughout the bloodstream. This information helps oncologists predict the stage of the tumor, which in turn determines whether or not the patient will be a good candidate for surgery.

Although CT scans can identify mesothelioma metastases, they do have some limitations. Several studies suggest that CT scans are less effective than MRIs at detecting cancer that has spread to the diaphragmatic muscle or the chest wall. Primary tumors and cancerous lymph nodes often blend together into one highlighted area on the CT image, and chest wall invasion can be difficult to distinguish from mediastinal fat. This makes it challenging for doctors to use a CT scan to accurately determine the tumor (T) and nodal (N) aspects of the TNM mesothelioma staging system.

CT Scan imaging

CT Scans are like x-rays, but take many more images in a precise and controlled fashion that permits the reconstruction of a 3-dimensional image. CT Scans are often taken in 'slices'. The patient may be given oral constrast and IV contrast to enhance the imaging of soft tissues.

Occluding factors aren't as much of an issue with CT scans as they are with x-rays, because the CT takes multiple fan-shaped images at each point as it rotates around the body, which is enough for a computer to reconstruct both the position and density of the objects in the body that absorb the x-rays.

Conventional CT scans are slow and require the patient to be immobilized during the scan. If the chest is being imaged, the patient may be told to hold his or her breath. Alignment problems between slices can sometimes miss a small mass that lies between slices. A conventional CT scan has a slice thickness of 8 mm to 10 mm.

Higher resolution CT scans, known as HRCT, helical CT and spiral CT, are much quicker. Instead of scanning each slice with the patient bed stationary, the bed is moving continuously as the CT scanner scans around the body (i.e., in a spiral pattern). This is fast enough that the patient doesn't need to hold his/her breath. It is also much higher resolution than conventional CT, so in many cases contrast dye will not be needed. A HRCT scan has a slice thickness of 1 mm to 1.3 mm.

A key limitation of HRCT is the higher resolution can lead to false positives. At higher resolutions more anomalies can be seen, but a much greater number of them turn out to be benign.

Another limitation of CT scanning in general is an inability to view very fine details in soft tissues such as muscles or ligaments. An MRI might be more appropriate in such situations.

Patient motion during a CT scan can cause the images to be "blurry". Also, any metal artifacts in the body can cause 'streaks' in the image. Flat tumors may also be harder to image with a CT scan. Scar tissue may also show up on a CT scan.

CT scanning is slower and more expensive than x-rays and ultrasounds. The radiation exposure from a whole-body CT scan is approximately 100 times that of a chest x-ray.

CT scans are not recommended for pregnant women. The intravenous contrast dye may not be recommended for patients who are allergic to iodine or shellfish.

Guidelines for Use of CT in Pregancy

The role of a radiologist is to estimate the fetal risk from known radiation dose from a particular examination and to help formulate a plan that provides minimal fetal radiation exposure but at the same time is able to accurately answer the clinical question. Table 3 presents a comparison of the guidelines proposed by the American Congress of Obstetricians and Gynecologists (ACOG) and those outlined by the ACR (10,14).

Recommendations by the ACOG and the ACR on Use of CT in Pregnancy

There are situations wherein the risk of irradiating the fetus is much less than the risk of not making a critical diagnosis in the mother (9,15), an assertion endorsed by the International Commission on Radiological Protection. For example, to evaluate the seriously injured pregnant patient with blunt abdominal trauma, CT (4) is the most accurate and cost-efficient diagnostic tool available (16,17). We are cautious when performing a CT examination in pregnant patients (11). At our institution, we use a low-dose CT protocol that entails reducing the scan range (if clinically allowable), decreasing the tube current, and increasing the pitch in comparison with those of the standard protocol. In some cases, it may be possible to reduce the kilovoltage without compromising image quality.

The radiation doses resulting in fetal anomalies and risks are far and above those typically seen in medical imaging, as shown in Table 1 (12). When medical imaging is being considered, radiation dose to the fetus is most concerning after multiple consecutive studies have been performed and the accumulation of radiation dose nears the threshold dose.

Overall, the best practice, as emphasized by the 2008 ACR practice guidelines for imaging pregnant or potentially pregnant adolescents and women with ionizing radiation, is as follows (10):

“To maintain a high standard of safety, particularly when imaging potentially pregnant patients, imaging radiation must be applied at levels as low as reasonably achievable (ALARA), while the degree of medical benefit must counterbalance the well-managed levels of risk.”

Radiation dose from a CT scan can be greatly reduced when proper technique is used.

CT Criteria for Adenoma

Several radiologic criteria can be used to diagnose an adenoma. The most well-known technique is to measure the mean attenuation value of the lesion. The rationale for this technique is based on a histologic feature of adenomas—that of abundant intracytoplasmatic lipid in the cortex. In contrast, malignant tumors of the adrenal gland have relatively little intracytoplasmic lipid, which can be detected by CT and MRI. A high correlation between lipid content and density measurements on CT has been shown, and when attenuation levels are between 10 HU and 15 HU or less on thin-section non-enhanced CT images, the diagnostic specificity approaches 100% . Although nonenhanced CT has a very high specificity, sensitivity is low, and higher attenuation values do not exclude the diagnosis of adenoma

Unfortunately, most CT examinations of the abdomen are performed after IV contrast, particularly if the indication is to look for metastatic disease, and mean attenuation measurements of adrenal adenomas may often be greater than 10 to 15 HU on postcontrast images. In this instance, looking at the contrast washout pattern of the adrenal lesion may help to diagnose an adenoma.

Studies have shown that adenomas show rapid washout of contrast when compared with nonadenomas and that this characteristic can be detected on delayed images acquired 10 to 15 minutes after the administration of IV contrast (Figure 10). If a relative washout of 40% to 50% is demonstrated, the test has a sensitivity of 83% to 93% and specificity of 93% to 98% for the diagnosis of an adenoma.An absolute washout of 60% is also highly specific and sensitive to make this differentiation. These parameters can be used to differentiate lesions that are nonspecific on nonenhanced CT (lipid-poor adenomas), as well as to characterize lesions identified only after the administration of IV contrast, when the use of a threshold of 10 HU or 15 HU is less likely to be useful for the diagnosis of adenoma.

Recently, a new method to detect the presence of fat within adrenal lesions was described by Bae et al. This study found that an accurate diagnosis of adenoma could be made using a histogram analysis method consisting of selecting a region of interest (ROI) within the adrenal mass and looking at the histogram distribution of pixel attenuation values. In this study, the presence of at least 10% negative pixels (ie, 10% lipid pixels) provided a specificity of virtually 100% for diagnosing adenoma. Although the sensitivity of this method was not high (reported to be 28%), the technique was found to have potential application in cases in which IV contrast was administered but delayed images were not available.

The heart in 3D CT Scan

Technological advances, ever-improving image quality and ever-shorter exposure times enabled CT to develop into one of the most important radiological diagnostic procedures within just a few years. It is used, for example if there is suspicion of bleeding, dilated/expanded blood vessels, a brain tumor or brain edema, or to check on degenerative or age-related changes/lesions, a possible stroke or a suspected fracture of the skull. Radiologists use the whole-body CT to search for tumors and cysts in the chest and abdomen – or to monitor the development of known tumors or changes in inner organs. Similarly, slipped discs, osteoporosis and other degenerative changes or bone fractures can be safely and quickly diagnosed with the help of computed tomography. A cardiac CT can generate a three-dimensional image of the coronary arteries and any changes in them. This method can be used to visualize calcifications and deposits in the coronary vessels, the first signs of atherosclerosis. A cardiac CT can show both the inside of the blood vessels and the walls. Further advantages stem from the three-dimensional nature of the image: the separate parts of the heart are shown in their true proportions. Moreover, the physician can turn the 3D object any way he or she wants. This makes it easier to recognize important details.

Advantages of CT Brain

 

 

• CT is much faster than MRI, making it the study of choice in cases of trauma and other acute neurological emergencies
• CT can be obtained at considerably less cost than MRI, and is sufficient to exclude many neurological disorders
• CT is less sensitive to patient motion during the examination. because the imaging can be performed much more rapidly
• CT may be easier to perform in claustrophobic or very heavy patients
• CT provides detailed evaluation of cortical bone
• CT allows accurate detection of calcification and metal foreign bodies
• CT can be performed at no risk to the patient with implantable medical devices, such as cardiac pacemakers, ferromagnetic vascular clips, and nerve stimulators

What happens during a CT scan?

You will remove any metallic objects which could diminish the quality of the images (this includes jewelry, glasses, dentures, and hair clips). You may also be asked remove your clothing and put on a patient gown. A technologist will help you to lie face up on the scanner table, with your head toward the “doughnut hole” of the CT scanner. The technologist will position you on the table, and a device to hold your head in place may be used. Then he or she leaves the exam room and goes to the control room, where you can still communicate by intercom.

An intravenous dye (contrast dye) may be given, through injection. This can help to highlight any areas of abnormality in the scan.

While CT images are being taken, it is important to lie still on the table, which will be moving very slowly in order to image the brain. It is normal for the CT scanner to make a whirring noise during the exam, so you should not be alarmed. The table will be moving a few millimeters at a time in order to obtain images of small slices of the brain, until the exam is finished. The procedure usually takes between 20 minutes and an hour.

Is a CT scan dangerous?

Far more X-rays are involved in a CT scan than in ordinary X-rays, so doctors do not recommend CT scans without a good medical reason.

However, the amount of radiation a patient is exposed to is small, and therefore are unlikely to cause any long term harm.

The risk is greatest to those who are pregnant, as radiation exposure can cause harm to the fetus, and therefore CT sans are contraindicated in pregnant women, unless the benefits of performing the scan far outweigh the risks.

Risks are also greater in children, when compared to adults, and therefore a CT is only recommended if a child has a serious condition that puts them at greater risk.

Some patients may experience side-effects due to allergic reactions to the liquid dye injected into the veins.

In very rare cases, this dye has been known to damage already weakened kidneys.

It is important to let the X-ray doctors or technicians know if you have any allergies, asthma or kidney trouble, prior to having the X-ray dye injected.

Does a CT scan hurt?

The examination does not hurt but some people find it uncomfortable to lie within the scanner itself.

Although the scanner is not tunnel shaped like an MRI scanner, people who suffer from severe claustrophobia sometimes have problems with CT scans. Let the doctors and radiographers know if this might be a problem.

Other people get slightly nervous because of the whirring noise the machine makes while working.

If the patient feels this might be the case, then this should be discussed prior to the procedure being carried out, since the patient may be unable to lie still during the scan therefore giving pictures of such poor quality they could not be interpreted anyway.

 

How does PET work?

PET stands for Positron Emission Tomography. PET scans measure metabolic activity and molecular function by using a radioactive glucose injection. The F-18 FDG is injected into the patient. The PET scanner detects the radiation emitted from the patient, and the computer generates three-dimensional images of tissue function or cell activity in the tissues of your body. These functional images can detect disease earlier than the anatomic information gained from CT alone. Like the CT scanner, your body will never come in contact with scanner itself. There are no side effects from this injection and procedure.

All cells use glucose as an energy source. However, cancer cells grow faster than normal healthy cells and they use glucose at much higher rate than normal cells. This is the basis of imaging with F-18 FDG for cancer detection in PET scan.

What is combined PET/CT scanning?

Combined PET/CT scanning joins two imaging tests, CT and positron emission tomography (PET), into one procedure. A PET scan creates colored pictures of chemical changes (metabolic activity) in tissues. Because cancerous tumors usually are more active than normal tissue, they appear different on a PET scan.

 

Combining CT with PET scanning may provide a more complete picture of a tumor’s location and growth or spread than either test alone. Researchers hope that the combined procedure will improve health care professionals’ ability to diagnose cancer, determine how far it has spread, and follow patients’ responses to treatment. The combined PET/CT scan may also reduce the number of additional imaging tests and other procedures a patient needs. However, this new technology is currently available only at some facilities. 

Risks of the CT Scan procedure

You may want to ask your doctor about the amount of radiation used during the CT procedure and the risks related to your particular situation. It is a good idea to keep a record of your past history of radiation exposure, such as previous CT scans and other types of X-rays, so that you can inform your doctor. Risks associated with radiation exposure may be related to the cumulative number of X-ray examinations and/or treatments over a long period of time.

If you are pregnant or suspect that you may be pregnant, you should notify your doctor. Radiation exposure during pregnancy may lead to birth defects.

If contrast dye is used, there is a risk for allergic reaction to the dye. Studies show that 85 percent of the population will not experience an adverse reaction from iodinated contrast; however, you will need to let your doctor know if you have ever had a reaction to any contrast dye, and/or any kidney problems. A reported seafood allergy is not considered to be a contraindication for iodinated contrast.

Patients with kidney failure or other kidney problems should notify their doctor In some cases, the contrast dye can cause kidney failure, especially if the patient has underlying kidney problems or is dehydrated. Patients taking the diabetes medication metformin (Glucophage), or its derivatives, with contrast are at risk for developing a condition called metabolic acidosis, an unsafe change in blood pH. The effects of kidney disease and contrast agents have attracted increased attention over the last decade, as patients with kidney disease are more prone to kidney damage after contrast exposure.

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

Medical issues to consider before a CT scan

Medical considerations prior to the CT scan may include:

• Tell the doctor if you are pregnant or think you may be pregnant. Another type of test may be recommended.
• Tell the doctor if you have allergies, diabetes, thyroid condition or renal (kidney) impairment.
• Tell the doctor if you experience claustrophobia (fear of small spaces). The doctor may give you mild sedatives to help you relax during the procedure.
• Tell the doctor about any implanted device you may have such as a pacemaker or medication pump, as metal objects may distort the images.
• Follow all the instructions you are given. Some CT scans require the use of contrast material to improve the image quality. The contrast material may be taken orally or by an intravenous injection (or both).
• You may have to go without food and drink for a certain length of time before the procedure. Your doctor will give you detailed instructions on how to prepare for the test and what to expect.
• A very obese person may be too big for the circular hole of the CT machine. The doctor may advise another type of medical imaging or diagnostic test.

Breastfeeding after a CT scan

Nursing mothers may need to avoid breastfeeding for about 24 hours after a CT scan, if the iodinated intravenous dye was used. This is because some of the ingredients in the dye can pass into your breastmilk and may be passed on to your baby. Tell your doctor or radiologist that you are breastfeeding before your CT scan and ask what they recommend.

What is Computed Tomography (CT Scan) ?

Computed Tomography (CT) is an imaging technique that uses x-rays to acquire very fine slices of data through the body. This data is then used to construct images of the body part and specific structures under examination. CT scans are only performed through the area of interest not the entire body.

At Southern Radiology you will be scanned on what is known as a multi-slice CT scanner. Multi-slice CT equipment acquires data and produces images of extraordinarily fine detail. The level of detail obtained allows the body part being scanned to be imaged in multiple directions and views including 3D representations.