Mutation - Smt. NHL Medical College : :

MUTATION - February 2006 | MUTATION - July 2006

MUTATION - October 2005

COMPARE AND CONTRAST : IMAGING TECHNIQUES

Rohan M. Desai (7th sem)

Diagnostic Imaging began with the discovery of X-Ray by Roentgen in 1895. Since then the field of radiology has progressed at a dramatic pace, more so in the last 25 years, and today we have a multitude of options to choose from when “searching” for the disease. Today we have at our disposal, besides X-Rays, CT-Scan, USG, MRI and a number of advances in these individual modalities. It is natural then for a question to arise when prescribing an investigation as to which modality will give the maximum information at minimum cost with most accuracy. We try to compare the “basic” modalities of today from a practical point of view in a problem-oriented approach.

X-Ray

Advantages Inexpensive Universally available Primary tool of investigation for any condition Many X-Ray based procedures - like IVP, Ba Swallow, HSG, MCUG	Disadvantages Uses radiation, prolonged exposure dangerous Contraindicated in pregnancy Gives only a 2-D impression Often multiple X-Rays required to understand a pathology

Main Applications Bone Pathology esp. fractures Chest Pathology Various Procedures mentioned above Polytrauma Per procedure - IITV Acute Abdomen Recent Advances Computerized Radiography: It has advantages like superior clarity, contrast, resolution. It shows soft-tissue better than normal X-Rays. Post-processing after exposure is possible reducing repetition.	“An X-Ray can perfectly diagnose an emergency condition like Pneumothorax, we need not waste time and money on costlier modalities.” “A perforated viscus leading to an acute abdomen is essentially a diagnosis by X-Ray which clearly shows gas under the diaphragm.”

Ultrasonography

Advantages Inexpensive, No radiation hazard Widely available Can be used as primary tool in combination with X-Rays for most conditions except neurological disorders	Disadvantages Highly subjective Bowel gas can interfere with evaluation and reduce sensitivity Not useful for structures surrounded by air or bone : chest, skull, spinal canal

Main Applications Pregnancy Acute abdomen, any abdominal condition Endoscopic USG ; Per-operative USG putting probe directly over viscera giving more accurate information Doppler information about vascular structure and abnormalities, non-invasive Echocardiography for cardiac evaluation FNAC/Biopsy under direct vision	“USG can be a very useful tool for evaluation of almost any abdominal pathology ” “However, Acute Pancreatitis is one of the major fallacies of USG. There may be perforation and gas leading to difficulty in diagnosis of Acute Pancreatitis. Also, it cannot differentiate between edematous and necrotizing pancreatitis - two conditions with very different outcomes”
Recent Advances Doppler, Echocardiography

CTSCAN

CAT Scan, developed in 1970 takes the idea of conventional X-Ray imaging to a new level. Instead of finding the outline of bones and organs, a CAT scan machine forms a full three-dimensional computer model of a patient’s insides.

Advantages Multiplanar - provides a true 3D picture Differentiates air, bone, soft tissue,fat clearly Very quick - whole body scan in seconds Good for hemorrhages and infarcts	Disadvantages Radiation hazard : C/I in pregnancy Not widely available Costly equipment,trained personnel required Not good for ligament, spinal cord imaging

Main Applications Brain injuries and pathologies Pneumonia, Pleural Effusion Chest malignancy (sometimes x-ray cannot differentiate chest mass from pneumonia) Liver & Pancreas pathology Intestinal Obstruction Fracture, dislocations esp. multiple fractures, to know if fracture is intra or extra-articular CT-guided biopsies and drainage procedures	Recent Advances MDCT - Multi-detector CT : sub-millimeter slices and sub-second scanning, can complete whole body scan in 15 seconds, available in Ahmedabad,. Brings with it completely new applications like Coronary Angiography, CT Urography etc. “Pregnancy is absolute C/I for X-Ray and CT”


MRI

On July 3, 1977, an event took place that would forever alter the landscape of modern medicine. Outside the medical research community, this event made scarcely a ripple at first. This event was the first MRI exam ever performed on a human being.

Advantages Multiplanar, No radiation Best for neurological, joint, ligament, soft tissue Can replace many conventional invasive procedures like myelography ERCP MRCP; MR Venography and MR Angiography are also available MRI contrasts have a very low incidence of side-effects Open MRIs now available for claustrophobic patients	Disadvantages Expensive, not widely available Absolute C/I is patient having pacemaker Relative C/I : metal implants in situ Takes longer time ~ 15 minutes for any examination Patient must lie absolutely still during imaging - otherwise image will be distorted Children need sedation Difficult in critically ill patients because life-saving equipment cannot be taken into MRI Console

Main Applications Neurological imaging : brain and spinal cord Joint diseases & Ligament pathologies MRI has an edge in detecting evolving strokes - earlier treatment can greatly alter prognosis Any body viscera pathology	Recent Advances Functional MRI (FMRI) is a technique that has recently been introduced to obtain functional information from the central nervous system. FMRI detects subtle increases in blood flow associated with activation of parts of the brain. FMRI may be useful for preoperative neurosurgical planning, epilepsy evaluation, and ”mapping” of the brain.

“MRI is not good for chest scanning because of its air-filled nature and because of its continuous movements during imaging giving rise to distorted pictures”	“An intervertebral disc that resembles a pocket of air in X-Ray is clearly seen on MRI”

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