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Interventional radiology uses medical imaging to guide instruments into the body for diagnosis or treatment. A biopsy can obtain material for diagnosis; a catheter can provide access for a therapeutic procedure. Guidance may use fluoroscopy, ultrasound, computed tomography or magnetic resonance imaging, depending on the instrument, target and procedure.^[ref]

The central measurement problem is localization. In an image-guided biopsy, seeing a suspicious region and seeing a needle separately is insufficient: the operator needs evidence that the sampling part of the needle reaches the intended region. A single X-ray projection collapses depth, so two objects can overlap on the image while remaining separated in the body. Choosing imaging views and following instrument motion addresses that geometric uncertainty. This explains why image guidance is more than taking a picture before an intervention.

An early therapeutic motivation was to use the access already provided by arterial catheters to treat obstructed vessels. Charles T. Dotter and Melvin P. Judkins's 1965 report described a percutaneous transluminal approach to arterial obstruction. Its developmental discussion connected contrast examinations and observed catheter pathways with the possibility of opening a passage through an obstructed region.^[ref]

The example connects anatomical imaging to mechanical action: identifying a narrowed path and changing that path are different tasks, but the same image-guided access can support both. The historical report motivates the method; it is not a procedure-selection rule for an individual patient.

Melvin P. Judkins was a radiologist who developed preshaped catheters and a percutaneous transfemoral method for selective coronary angiography. His work connected catheter geometry, vascular anatomy and X-ray recording: the instrument had to reach a particular arterial opening, while the imaging system had to record the contrast-filled vessels.^[ref]

His 1967 report Selective Coronary Arteriography: Part I: A Percutaneous Transfemoral Technic by Melvin P. Judkins described 100 consecutive patients examined for suspected coronary disease. Both coronary arteries were selectively catheterized from femoral access, and contrast injections were recorded by direct serial radiography and cine imaging. The methods describe forming catheter shapes over preformed bending wires, showing that the instrument's geometry was an engineered part of the measurement rather than an incidental tube.^[ref]

For an illustrative contrast experiment, imagine comparing a broad injection upstream with a small injection at the opening of one branch. The latter changes where contrast first enters and can make the selected branch easier to distinguish. That qualitative comparison explains the word selective; it does not specify a safe injection protocol or claim equal performance in every anatomical arrangement.

Judkins also collaborated with Charles T. Dotter on transluminal treatment of arterial obstruction, linking diagnostic access to the possibility of treatment through a catheter.^[ref] His preshaped coronary instruments and the joint obstruction work are related contributions, but they address different immediate tasks: delineating a vessel and changing an obstructed passage.