Non contrast-enhanced MRA versus ultrasound blood vessel assessment to determine the choice of hemodialysis vascular access.

PURPOSE: The aim of this work was to establish the relationship between traditional blood vessel mapping for vascular access (VA) creation by B-mode ultrasound (US) and novel non contrast-enhanced magnetic resonance angiography (NCE-MRA), and to study the potential influence of the diameter assessment technique on the choice of hemodialysis vascular access. METHODS: A total of 27 end-stage renal-disease patients were included. They received routine US and a NCE-MRA examination of the upper extremity. Diameters were measured manually on US and semi-automatically on NCE-MRA. These measurements were statistically compared for the arteries and veins and for each measurement location. Furthermore, sensitivity and specificity of both modalities to predict VA location was investigated by comparison with an experienced surgeon. This analysis gave insight into the potential influence of vessel mapping modality on decision-making. RESULTS: Comparison of NCE-MRA with US for the arteries and veins, demonstrated a bias of 9% (limits -33%-78%) and 38% (limits -36%-198%), respectively. Statistically significant differences between the modalities on the individual locations were mainly found for the venous locations. The sensitivity and specificity for US to predict VA location was 1.0 and 0.74, respectively, while for NCE-MRA this was 0.88 and 0.39, respectively. CONCLUSIONS: The results obtained indicate that extreme caution should be exercised when replacing one diameter measurement modality with the other. A further need exists to improve both vessel mapping protocols to obtain a geometric description of the upper extremity vasculature regardless of acquisition modality.

The benefit of non contrast-enhanced magnetic resonance angiography for predicting vascular access surgery outcome: a computer model perspective.

INTRODUCTION: Vascular access (VA) surgery, a prerequisite for hemodialysis treatment of end-stage renal-disease (ESRD) patients, is hampered by complication rates, which are frequently related to flow enhancement. To assist in VA surgery planning, a patient-specific computer model for postoperative flow enhancement was developed. The purpose of this study is to assess the benefit of non contrast-enhanced magnetic resonance angiography (NCE-MRA) data as patient-specific geometrical input for the model-based prediction of surgery outcome. METHODS: 25 ESRD patients were included in this study. All patients received a NCE-MRA examination of the upper extremity blood vessels in addition to routine ultrasound (US). Local arterial radii were assessed from NCE-MRA and converted to model input using a linear fit per artery. Venous radii were determined with US. The effect of radius measurement uncertainty on model predictions was accounted for by performing Monte-Carlo simulations. The resulting flow prediction interval of the computer model was compared with the postoperative flow obtained from US. Patients with no overlap between model-based prediction and postoperative measurement were further analyzed to determine whether an increase in geometrical detail improved computer model prediction. RESULTS: Overlap between postoperative flows and model-based predictions was obtained for 71% of patients. Detailed inspection of non-overlapping cases revealed that the geometrical details that could be assessed from NCE-MRA explained most of the differences, and moreover, upon addition of these details in the computer model the flow predictions improved. CONCLUSIONS: The results demonstrate clearly that NCE-MRA does provide valuable geometrical information for VA surgery planning. Therefore, it is recommended to use this modality, at least for patients at risk for local or global narrowing of the blood vessels as well as for patients for whom an US-based model prediction would not overlap with surgical choice, as the geometrical details are crucial for obtaining accurate flow predictions.

Accuracy and precision of vessel area assessment: manual versus automatic lumen delineation based on full-width at half-maximum.

PURPOSE: To evaluate the accuracy and precision of manual and automatic blood vessel diameter measurements, a quantitative comparison was conducted, using both phantom and clinical 3D magnetic resonance angiography (MRA) data. Since diameters are often manually measured, which likely is influenced by operator dependency, automatic lumen delineation, based on the full-width at half-maximum (FWHM), could improve these measurements. MATERIALS AND METHODS: Manual and automatic diameter assessments were compared, using MRA data from a vascular phantom (geometry obtained with µCT) and clinical MRA data. The diameters were manually assessed by 15 MRA experts, using both caliper and contour tools. To translate the experimental results to clinical practice, the precision obtained using phantom data was compared to the precision obtained with clinical data. RESULTS: A diameter error <10% was obtained with resolutions above 2, 3, and 5 pixels/diameter for the automatic FWHM, contour, and caliper methods, respectively. Using phantom data, precision of the manual methods was low (error >20%), even at high resolutions, while precision for the automatic method was high (error <3%) when using more than 2 pixels/diameter. A similar trend was found with clinical data. CONCLUSION: The results obtained clearly demonstrate improvement in the accuracy and precision of vessel diameter measurements with use of the automatic FWHM-based method.