Sunday, August 28, 2011

Diagnosing and Staging Pancreatic Cancer with Imaging Techniques


Pancreatic cancer usually goes undetected until it's advanced. By the time symptoms occur, diagnosing pancreatic cancer is usually relatively straightforward. Unfortunately, a cure is rarely possible at that point.

The goal, of course, is detection and diagnosis at the earliest time possible. How pancreatic cancer is diagnosed, and is early detection of pancreatic cancer possible?

Diagnosing pancreatic cancer usually happens when someone comes to the doctor after experiencing weeks or months of symptoms. Pancreatic cancer symptoms frequently include abdominal pain, weight loss, or jaundice (yellow skin). A doctor then embarks on a search for the cause, using the tools of the trade:
  • By taking a medical history, a doctor learns the story of the illness, such as family medical history, the time of onset, nature and location of pain, smoking history, and other medical problems.
  • During a physical examination, a doctor might feel a mass in the belly, notice jaundiced skin, or weight loss.
  • Lab tests could show evidence that bile flow is being blocked, or other abnormalities.

Imaging Techniques

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Advances in imaging technologies have been key to improving the detection and treatment of pancreatic cancer. Here are some of the imaging techniques which can be used:

Ultrasound

Ultrasound uses high-frequency sound waves to create moving images of your internal organs, including your pancreas. The ultrasound sensor (transducer) is placed on your upper abdomen to obtain images.

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Computed Tomography (CT)

Doctors first determine the extent of the disease through CT scanning, an accurate method of diagnosing and staging pancreatic cancer. Doctors have developed a highly accurate CT scanning method that involves injecting a contrast material (dye) to obtain a better image. This method also reduces the amount of radiation required while improving diagnostic accuracy to a level approaching that of invasive procedures such as angiography.

The Helical ("Spiral") CT Scan 

The helical ("spiral") CT scan is now the best overall study for diagnosis and preoperative staging. It provides information about the nature and site of the lesion (e.g., pancreatic vs. other periampullary tumors, bile duct tumors), its resectability (e.g., liver metastases, vascular invasion), and vascular anatomy. It is important to stress that the helical CT is the current state of the art. When the helical CT is compared with the conventional technique, and especially when imaging of both the pancreas and liver is done separately according to published protocols, the differences in the sensitivity and specificity of the two approaches is dramatic. The primary lesion itself as well as liver metastases may be evident with the helical CT, and these may not be seen with the standard scan. Extraordinary detail is provided about vascular anatomy and vascular invasion by tumor.

Positron Emission Tomography (PET Scan)

PET scans involve injecting a form of sugar that contains a radioactive atom into the blood. Cancer cells absorb large amounts of this sugar. A special camera can show where these cells are. This test is useful to see whether the cancer has spread to the lymph nodes or other places.

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PET/CT Scan

This new test combines the two types of scans to even better pinpoint the tumor. This test may be especially useful for spotting cancer that has spread beyond the pancreas and can't be removed by surgery. It may also be useful for staging the cancer. It may even be able to spot early cancer.

Magnetic Resonance Imaging (MRI)

MRI may be useful in staging pancreatic cancer for selected patients, particularly those in whom major blood vessels are compressed or invaded by cancer.

MRI scans use radio waves and strong magnets instead of x-rays to take pictures. MRI scans are helpful in looking at the brain and spinal cord. MRI scans take longer than CT scans—often up to an hour. Also, you have to lie inside a narrow tube, which can be upsetting for some people. Newer, "open" MRI machines can help with this if needed. The machine also makes a loud thumping noise. Some places will give you headphones with music to block it out.

Most doctors prefer CT scans to look at the pancreas, but an MRI may sometimes give more information.

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Magnetic Resonance Cholangiopancreatography (MRCP)

A type of MRI, MRCP allows the physician to get a picture of the pancreatic ducts, the internal channels of the pancreas that are a prime target of tumors.

Endoscopic Ultrasound (EUS)

Similar to endoscopy, EUS involves the insertion of a thin tube through the mouth and into the stomach. At the tip of the tube is a small ultrasound probe that bounces sound waves off the walls of the stomach. Because the stomach is located next to the pancreas, EUS provides highly detailed pictures of the pancreas. This method can be extremely useful in evaluating pancreatic masses or cysts and can assist in removing pancreatic cells and fluid for analysis.

Endoscopic ultrasound (EUS) is not likely to be used as a first line diagnostic study in most patients with pancreatic cancer. However, once the diagnosis is suspected, it can provide valuable information about whether the pancreatic cancer has invaded adjacent vessels like the superior mesenteric vein. This is important in decisions about resection, and whether the patient is a candidate for operation. EUS also may detect smaller tumors than those currently detectable by CT scanning techniques, and it permits accurate placement of biopsy needles (e.g., fine needle aspiration cytology) if there is need to establish the diagnosis.

Endoscopic Retrograde Cholangiopancreatography (ERCP)

As in EUS, an endoscope is passed through the patient's mouth. This procedure uses a dye to highlight the bile ducts in your pancreas. During ERCP, a thin, flexible tube (endoscope) is gently passed down your throat, through your stomach and into the upper part of your small intestine. Air is used to inflate your intestinal tract so that your doctor can more easily see the openings of your pancreatic and bile ducts. A dye is then injected into the ducts through a small hollow tube (catheter) that's passed through the endoscope. Finally, X-rays are taken of the ducts. A tissue or cell sample (biopsy) can be collected during ERCP. ERCP also can be used therapeutically, for placement of a bile duct stent to relieve jaundice.

Percutaneous transhepatic cholangiography (PTC)

PTC uses a dye to highlight the bile ducts in your liver. Your doctor carefully inserts a thin needle into your liver and injects the dye into the bile ducts. A special X-ray machine (fluoroscope) tracks the dye as it moves through the ducts.

Angiography

This is a type of X-ray used to look at blood vessels. This test can show whether blood flow in an area is blocked or slowed by a tumor. It can also show if there are any abnormal blood vessels. The results help the doctor decide whether the cancer can be removed and plan the surgery.

Angiography can be uncomfortable because the radiologist who does it has to put a small tube (called a catheter) into the artery leading to the pancreas. Usually the catheter is put into an artery in the inner thigh and threaded up to the pancreas. A local anesthetic is often used to numb the area before putting in the catheter. Then the dye is injected quickly to outline all the vessels while the X-rays are being taken.

Optical coherence tomography (OCT)

A team of researchers from four Boston-area institutions led by Nicusor Iftimia from Physical Sciences, Inc. has demonstrated for the first time that optical coherence tomography (OCT), a high resolution optical imaging technique that works by bouncing near-infrared laser light off biological tissue, can reliably distinguish between pancreatic cysts that are low-risk and high-risk for becoming malignant. Other optical techniques often fail to provide images that are clear enough for doctors to differentiate between the two types.


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