CONTRAST AGENTS (DYE) IN RADIOLOGY

Certain radiological exams require a special medication called as “dye” or “contrast agents”. These are “Imaging-related medications” and are designated as “prescription drugs” in accordance with Food and Drug Administration (FDA).  

Contrast helps certain areas to show up better and highlight tissues and organs that would not be visible otherwise. This allows the radiologist to distinguish normal from abnormal conditions. 

A simple example would be: difference between a color and black &white picture.  A color picture has more details and much more information can be extracted (see fig. 1 a and 1 b). 

Fig. 1a: B& W picture of sunset                       Fig. 1b: Color picture of sunset

Similarly, when introduced into the body prior to an imaging exam, contrast materials make certain structures or tissues in the body appear different on the images, then they would appear, if no contrast material had been administered. Fig. 2 b shows, a tumor in the abdomen (red arrow). It is easily identified after giving contrast during a CT scan if compared to fig. 2 a. 

Fig. 2a: Non contrast CT                         Fig. 2b: Contrast CT shows tumor (red arrow).

Administration of dye, causes organs and tissues to show up better and allowing them to stand out. Thus "contrast selected areas" of the body are easily distinguished form other surrounding tissues. This leads to improved visibility of specific organs, blood vessels or tissues. This helps a radiologist diagnose medical conditions so that treatment can be started early by your physician.   You foresee a problem, before it manifests!

There are different types of contrast agents used for various imaging procedures like:

1.      Barium is used for study of intestine like in barium follow through for small intestine.

2.      Iodinated contrast agents administered for IVP (intra venous pyelography) or CT scan.

3.      Paramagnetic agents like gadolinium administered during MRI.

These contrast agents can be given through different routes like:

1.      Orally or rectally for barium procedures.

2.      Injected through a vein or artery.

3.      Injected into a body cavity under image guidance.

Contrast Radiography helps answer important questions about the health and functioning of vital organs. The phenomenon of present-day radiologic imaging would be lacking without these agents.

References:

1.      http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_contrast

2.      http://www.hillcrestcushing.com/contrast-radiology

3.      Jill M. Widmark, Imaging-related medications: a class overview. proc (bayl univ med cent). oct 2007; 20(4): 408–417. pmcid: pmc2014815.

Radiology and biopsy:

What is biopsy?

Biopsy is a medical procedure, whereas tissue from a diseased organ in the body is removed by doctors which is then subjected to assessment by pathologist under microscope. It is one of the final and confirmatory step in making a diagnosis. In cancer treatment, biopsy is corner stone in deciding the treatment plan.

How is biopsy done?

To obtain tissue sample form the body the doctor needs to reach that organ and take a small sample. This can be done by various ways, like open surgery, key hole surgical technique like laparoscopy, by entering a cavity like endoscopy (putting a scope in the stomach) or putting a needle in body part without surgery. 

What is the role of radiology in biopsy?

Some of the tissues are directly accessible like a growth on the skin and do not need guidance (eg. Punch biopsy of a skin lesion). However, when an internal organ need to be biopsied, guidance is required to visualize the structure and biopsy it with minimal invasion and precision to minimize injury to normal structures. This is where radiology plays an important role to guide the needle at its target using imaging technology.

How do radiologist perform a biopsy?

A radiologist who performs a biopsy is called as “interventional radiologist” (as he or she intervenes). Radiologist use their knowledge and skill of imaging techniques to visualize the abnormal area or diseased organ. It is done with help of X-Ray fluoroscopy, ultrasound, CT scan, MRI or even PET CT. First the organ is imaged and exact target for biopsy is identified. 

Coordinates such as the depth and the angle of the needle to enter are planned based on the scan images. The needle entry, its depth and tip is monitored by one of the imaging technique. For eg. Ultrasound or CT scan. Once the desired target is reached, the biopsy is performed and the sample is removed and sent to the pathologist. The entire procedure is done under sterile conditions and when required under some kind of local anesthesia. Using such approach, it is minimally invasive and patients are able to go home same day after being in observation for some time. 

The image provided below is a representative and not of an actual biopsy. The blue arrow is representative of a needle tract (depth, angle etc.). The abnormal area (mass) is the target for biopsy. CT scan is able to differentiate between healthy organ and diseased organ.