CT measurements of capillary permeability within nodal masses: a potential technique for assessing the activity of lymphoma.

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Abstract
Analysis of time-attenuation data has enabled CT to measure capillary permeability within the brain and kidney. As yet, such techniques have not been applied to nodal masses in patients with lymphoma. Tumour angiogenesis is known to produce capillaries that exhibit increased permeability and CT measurements of permeability could therefore potentially provide a marker of tumour viability. This study aims to determine the feasibility and limitations of CT measurement of capillary permeability within lymphoma nodal masses. Six patients with biopsy proven lymphoma have been studied. Time-attenuation curves from the aorta and nodal mass were generated from a single-location dynamic sequence of images acquired over 3 min following an intravenous bolus of iopamidol. A nuclear medicine data processing technique, Patlak analysis, was used to calculate capillary permeability and blood volume within the nodal mass. Renal blood vessel permeability was also determined in four patients. Median lymph node permeability to iopamidol was 88.5 microliters min-1 ml-1 (range 36.4-198.5 microliters min-1 ml-1). The correlation coefficient of the linear fit for the Patlak analysis ranged from 0.74 to 0.95 and was greater than 0.9 for regions of interest of 150 pixels or more (256 x 256 matrix). The values for renal permeability (442 microliters min-1 ml-1; range: 349-589 microliters min-1 ml-1) were comparable to those previously reported. Functional images of permeability were also obtained. The study has confirmed the feasibility of CT measurements of capillary permeability within nodal masses. The technique combines anatomical imaging and functional information within one examination and has potential application in monitoring the response of lymphoma to therapy.