Evolving role of radiologists

The role that today’s radiologist is expected to play is much more decisive and sometimes even proactive, says, Dr Kumar K S, Consultant – Interventional Radiology and Interventional Oncology, Cytecare

Most technological progress in radiology and imaging in the past few decades has been in the direction of clearer and sharper images, safety (and convenience) of patients, steadily decreasing radiation doses and so on. This has resulted in the development of molecular imaging techniques such as MR spectroscopy and PET/CT on one hand and the entire field of interventional radiology (IR) on the other. Together they have also allowed the radiologist and imaging specialist to play a significant role in planning and implementing  the therapy for most forms of cancer.

Interventional radiology

A significant number of pioneering developments in the field of medicine and surgery have involved IR in one form or another.  Medical procedures such as angiography and angioplasty (coronary as well as peripheral) would be difficult to imagine without the participation of an IR specialist.

According to a factsheet published by the Fairfax, Virginia-based Society for Interventional Radiology (SIR), some recent advances in IR include:

• Non-surgical ablation of tumour cells without damage to surrounding healthy tissue
• Embolisation to cut off the blood supply to neoplastic tissue
• Vascular interventions including stenting, already mentioned above
• Thrombolysis with the help of a catheter to restore blood supply to a limb extremity

Chemo-embolisation

An important addition to an IR specialist’s arsenal in recent years is chemo-embolisation, which is a technique for delivering anti-cancer drugs directly into a tumour. In addition, it enables the physician to occlude the blood vessel supplying the tumour cells and thus starve the malignant cells of vital nutrients and oxygen. The method is most commonly used for the treatment of liver cancer or metastasis to the liver from cancer located in other organs.

Chemo-embolisation is particularly suited to liver cancer because of the unusual vascular arrangement: the portal vein supplies blood to the normal liver cells, while the malignant cells receive their blood supply through the hepatic artery.

The actual technique involves passing a catheter through an artery in the groin, much in the same way as it is done during an angioplasty. The catheter is then guided with the help of expert imaging to the hepatic system.  Thus, a modified version of the same technique is also useful in colon cancer, carcinoid tumours, ocular melanoma, or even primary tumours in other parts of the body.

Other applications of IR

IR can be put to good use in several other clinical situations as well. Examples are cancer of the breast, the prostate gland, the pancreas and several others. MRI-guided biopsy of the prostate gland is performed either through the rectal route with the patient lying on the back or using the perineal route. In the latter, the guidance grid is placed just below the scrotum and the tissue to be examined is removed with the help of a biopsy gun. A very similar procedure is used in MRI-guided breast biopsy where the MRI is used to locate the suspected breast lump and the tissue sample is drawn through a needle.

In suspected cases of lung cancer, the nodule or swelling to be examined is located with the help of CT and the tissue is removed through a biopsy needle. As in the case of breast cancer, the procedure is much less traumatic and invasive than a convention surgical biopsy.

Pancreatic cancer is difficult to distinguish from chronic pancreatitis, pancreatic cysts, gall bladder stones and other conditions. For this, special CT and MRI scan techniques have been developed. A particularly useful test is MR-cholangiopancreatography, which implies an examination of the pancreas, the bile duct, the pancreatic duct and other surrounding structures with the help of MRI. In many such cases, however, MRI is best used as an adjunct to CT rather than a substitute.

Stages of development

The early IR procedures that took place in the 1960s and 1970s were angioplasty of peripheral vessels, early stenting procedures, heparinised guide-wires for thrombolysis, embolisation of variceal bleeding in the GI tract, and so on. In 1978, Charles Dotter, who is described till today as the Father  of  IR, was awarded the Nobel Prize for his work in the field.

During the 40-50 years that have gone by since then, IR has made tremendous strides in alleviating the suffering of human beings afflicted with diseases of various organs: the liver and hepatic system, the GI tract, pancreas and spleen, the kidney and uro-genital system and so on. This has made IR one of the most dynamic areas of medical advancement, scientific as well as technological, apart from making it a Board-certified specialty in the US.

However, most patients do not come into contact with IR specialists who get almost all their work through surgeons practicing in different clinical specialties. The SIR leaders hope that with the passage of time and a better understanding of IR work, primary care physicians will refer patients directly to them. That is when IR would really come into its own.

Development of CT and MRI

Computerised Tomography (CT) also known as Computerised Axial Tomography (CAT) was first developed in the 1970s under Sir Godfrey Hounsfield. It depends on a series of X-rays at very short intervals that are then integrated to create a complete image of the organ under examination. Later, it would be combined with special software to generate 3D images including coronary arteries (CT-angiography). Another direction of development was to combine CT with Positron Emission Tomography (PET) to create PET/ CT.

Nuclear Magnetic Resonance (NMR) imaging, later renamed as Magnetic Resonance Imaging (MRI), was first discovered in 1946 but really started becoming useful in 1973. That year, Paul Lauterbur demonstrated that the interaction of radiofrequency and magnetic fields could be utilised for imaging purposes. Soon, the technique was improved by other scientists till the images obtained were comparable to CT images and could therefore be harnessed for clinical applications.

Molecular imaging

While IR is more focused on minimally invasive procedures for imaging of anatomical structures and in delivering or facilitating various treatment modalities, Molecular Imaging (MI) is more about examining biochemical activity at the cellular level.

MI can help the treating physician at several stages of managing a disease, particularly the different forms of cancer. It can not only help to diagnose the disease at very early stages, and determine the stage to which the disease has progressed, but also help the medical team to decide which therapy would be most suitable to an individual patient. Besides, it enables the physicians to examine the progress or remission of the disease and to discover whether it has spread to distant locations within the body.

Two important components of MI are Nuclear Medicine and PET/ CT. Nuclear Medicine, which also took birth during the 1950s, underwent considerable improvements in the years that followed. Here the source of the X-rays is a set of radioactive compounds instead of an X-ray tube.

PET scanning depends on emission of positrons, which are positively-charged electrons, as opposed to ‘normal’ electrons which are negatively charged. When the positron meets an electron, it is destroyed and the time needed for this to happen can be recorded through specially designed detectors.

A majority of PET equipment works with a positron-emitting isotope of fluorine (F-18) incorporated into a glucose analog called fluorodeoxyglucose (FDG). Because cancer cells take up more glucose than normal cells, FDG can help PET to detect these cells with accuracy. Hence, it is widely used to diagnose both primary malignancy and metastasis to other parts of the body.

The combination of PET with CT forms the basis for PET/CT. The two sets of images, the FDG-based from PET and X-ray images obtained through CT are integrated with the help of special software to produce details of both the structural and functional aspects of the tissues or organs under examination. PET/CT is useful for examining cancers in various parts of the body including the lungs, ovaries, prostate, etc.

Conclusion

With all these investigative options available for the hospital physicians in general,  and the radiologist in particular, treatment of most cancers has become a multi-disciplinary exercise. Thus, the radiologist can at times help the oncologist and onco-surgeon to decide whether a vacuum-assisted biopsy is sufficient (in breast cancer) or a surgical biopsy is needed. Similarly, in some cancers where neo-adjuvant therapy is being used, MI can help to evaluate whether the therapy is effective or not. Likewise, there are times when the pathologist’s findings may not support that of the radiologist or vice-versa. The medical team could then have to revisit their entire strategy. Thus, the role that today’s radiologist is expected to play is much more decisive and sometimes even proactive than what it used to be a few decades ago.