Joint Program in Nuclear Medicine

Nuclear Medicine Vascular Flow Studies

Keir Hales, MD
Annick D. Van den Abbeele, MD

March 14, 2000

Presentation

A 45 year old man with non Hogkin’s lymphoma, who was undergoing intravenous chemotherapy infused through a right internal jugular catheter, noticed swelling of the right arm and right neck. The infusion nurse noted poor blood return when drawing back through the catheter. The patient referred for evaluated with a catheter flow study.

Imaging Technique

Camera Setup

Administration Technique

Imaging Findings

After injection of both antecubital veins, a representative frame from the cine demonstrates obstruction to flow at the junction of the subclavian and brachiocephalic veins bilaterally (shown by arrows). A collateral vessel can be seen coursing serpiginously from the right subclavian vein (arrowhead) to the heart (concave arrowhead), which can be faintly seen.

Diagnosis

A large catheter induced clot at the junction of the subclavian and brachiocephalic veins bilaterally obstructs blood return to the superior vena cava.

Discussion

Indications

There are several indications for nuclear medicine flow studies. While some of the original indications such as the noninvasive evaluation of vascular flow, and the evaluation of regional perfusion in organs and extremities have largely been supplanted by ultrasound, the evaluation of venous catheters remains an important indication because ultrasound is difficult through the bony upper thorax and central vessels. The flow characteristics of central lines, Porta-caths, Hickman, plasmapharesis catheters and PICC lines can be easily obtained.

Radiopharmaceuticals

Flow studies may be performed with Tc-99m-DTPA, which yields a whole body dose of 0.15 rads/25 mCi, or Tc-99m-pertechnetate, which yields a whole body dose of 0.30 rads/25 mCi. Either study requires 1-4 injections of 5-8 mCi per injection. If Tc-99m-pertechnetate is used, the thyroid is blocked with 200-400mg potassium perchlorate P.O. 10 mins before the study.

Interpretation

A familiarity with normal vascular anatomy of the central vessels is required to identify abnormal flow patterns. Several types of flow pattern may be observed.

Venous occlusion by the presence of the catheter may be partial or complete. The increase in flow resistance is seen as tracer impedance during imaging. The physiologic response to increased resistance is the formation of collateral pathways as alternative routes for blood return to the heart. While often seen as irregular or disorganized vascular routes, some collaterals have similar pathways to the native vessels, and can only be identified by subtle displacement of the expected course, or the observation of reverse flow within the vessels.

Catheter occlusion is manifest by increased tracer impedance or in extreme cases, retrograde flow during the injection of tracer into the catheter. While a completely occluded catheter is clinically apparent, the ability to infuse but not draw back through the catheter may suggest the presence of a fibrin sheath. The persistence of tracer at the tip of the catheter after the injection is a typical scintigraphic finding.

Catheter malfunction may result in cracks in the catheter tubing or disconnection of the catheter from the infusion port with tracer extravasation into surrounding tissues. Catheter malposition may result from incorrect positioning or catheter migration.

Not all abnormal flow patterns are catheter related. Many physiologic variants can simulate disease. Venous anomalies are not uncommon and an asymptomatic left arch or duplex SVC may give the position of malposition. Post surgical changes such as pneumonectomy, or vascular ligation may alter blood flow. Chemotherapy can induce vascular sclerosis, and frequent catheter placement can result in vascular fibrosis.

Treatment

Treatment often requires anticoagulation. 2mg TPA in 2cc saline is instilled in the catheter and withdrawn after 2 hours. Alternatively, Urokinase and heparin can be used. Fibrin sheaths may be stripped from the catheter tip using interventional radiology techniques, or the catheter may be simply exchanged and inserted in a new location.

References

1. Martin P, Glass EC, Villarica j: Peripheral raionuclide angiography. J Am Med Assoc 242:1781-1784, 1979.

2. Procedure Manual Nuclear Medicine, DFCI

3. Chemotherapy induction center protocols and procedures, DFCI

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J. Anthony Parker, MD PhD, Tony_Parker@CareGroup.Harvard.edu