An en bloc approach to CT perfusion for the evaluation of limb ischemia

An Overview of Clinical Examinations in the Evaluation and Assessment of Arterial and Venous Insufficiency Wounds

Arterial and venous insufficiency are two major causes of chronic wounds with different etiology, pathophysiology, and clinical manifestations. With recent advancements in clinical examination, clinicians are able to obtain an accurate diagnosis of the underlying disease, which plays an important role in the treatment planning and management of patients. Arterial ulcers are mainly caused by peripheral artery diseases (PADs), which are traditionally examined by physical examination and non-invasive arterial Doppler studies. However, advanced imaging modalities, such as computed tomography angiography (CTA) and indocyanine green (ICG) angiography, have become important studies as part of a comprehensive diagnostic process. On the other hand, chronic wounds caused by venous insufficiency are mainly evaluated by duplex ultrasonography and venography. Several scoring systems, including Clinical-Etiology-Anatomy-Pathophysiology (CEAP) classification, the Venous Clinical Severity Score (VCSS), the Venous Disability Score, and the Venous Segmental Disease Score (VSDS) are useful in defining disease progression. In this review, we provide a comprehensive overlook of the most widely used and available clinical examinations for arterial and venous insufficiency wounds.

Perfusion imaging techniques in lower extremity peripheral arterial disease

Lower limb peripheral arterial disease (PAD) characterizes the impairment of blood flow to extremities caused by arterial stenoses or occlusions. Evaluation of PAD is based on clinical examination, calculation of ankle-brachial index and imaging studies such as ultrasound, CT, MRI and digital subtraction angiography. These modalities provide significant information about location, extension and severity of macrovasular lesions in lower extremity arterial system. However, they can be also used to evaluate limb perfusion, using appropriate techniques and protocols. This information may be valuable for assessment of the severity of ischemia and detection of hypoperfused areas. Moreover, they can be used for planning of revascularization strategy in patients with severe PAD and evaluation of therapeutic outcome. These techniques may also determine prognosis and amputation risk in patients with PAD. This review gives a basic overview of the perfusion techniques for lower limbs provided by imaging modalities such as ultrasound, CT, MRI, digital subtraction angiography and scintigraphy and their clinical applications for evaluation of PAD and revascularization outcome.

Noninvasive assessment of foot perfusion in cholesterol-fed rabbits using dynamic volume perfusion CT with an upslope method

To evaluate the feasibility of dynamic foot volume CT with the upslope method and to demonstrate macrovascular reactivity and microvascular perfusion during cuff-induced reactive hyperemia state in cholesterol-fed rabbits. 30 New Zealand male rabbits were divided into 2 groups: dietary hypercholesterolemia (n = 10) and normal diet control (n = 20). To measure for macrovascular reactivity, perfusion parameters of the left posterior tibial artery was measured at baseline and at reactive hyperemia state. For the evaluation of microvascular perfusion, color-coded perfusion map of the plantar dermis was generated for perfusion CT scan by an in-house developed dedicated analysis software based on upslope method. Dermal perfusion values were measured and analyzed before and after cuff-induced reactive hyperemia. Foot dynamic volume CT with the upslope method demonstrated significant impairment of both macrovascular reactivity and microvascular perfusion in cholesterol-fed rabbits without significant macrovascular lesions during cuff-induced reactive hyperemia (CRH) state. Arterial time-to-peak of cholesterol-fed rabbits failed to show acceleration while chow-fed rabbits showed significant decrease in time. Microvascular perfusion calculated by perfusion value (P < 0.01) and perfusion ratio (P = .014) showed decreased microvascular perfusion in cholesterol-fed rabbits compared to chow-fed rabbits during CRH state. Post-CT pathologic examination revealed decreased endothelial cell density in cholesterol-fed rabbits (P < 0.001). Foot perfusion CT using upslope method provides perfusion parameters for large arteries and a perfusion map of the foot during cuff-induced reactive hyperemia in cholesterol-fed rabbits. It may be a useful tool to assess microvascular reactivity in patients with peripheral artery disease but no apparent macrovascular lesions.

CT perfusion in peripheral arterial disease-hemodynamic differences before and after revascularisation

Objectives

The purpose of this study was the assessment of volumetric CT perfusion (CTP) of the lower leg musculature in patients with symptomatic peripheral arterial disease (PAD) before and after interventional revascularisation.

Methods

Twenty-nine consecutive patients with symptomatic PAD of the lower extremities requiring interventional revascularisation were assessed prospectively. All patients underwent a CTP scan of the lower leg, and hemodynamic and angiographic assessment, before and after intervention. Ankle-brachial pressure index (ABI) was determined. CTP parameters were calculated with a perfusion software, acting on a no outflow assumption. A sequential two-compartment model was used. Differences in CTP parameters were assessed with non-parametric tests.

Results

The cohort consisted of 24 subjects with an occlusion, and five with a high-grade stenosis. The mean blood flow before/after (BFpre and BFpost, respectively) was 7.42 ± 2.66 and 10.95 ± 6.64 ml/100 ml*min⁻¹. The mean blood volume before/after (BVpre and BVpost, respectively) was 0.71 ± 0.35 and 1.25 ± 1.07 ml/100 ml. BFpost and BVpost were significantly higher than BFpre and BVpre in the treated limb (p = 0.003 and 0.02, respectively), but not in the untreated limb (p = 0.641 and 0.719, respectively).

Conclusions

CTP seems feasible for assessing hemodynamic differences in calf muscles before and after revascularisation in patients with symptomatic PAD. We could show that CTP parameters BF and BV are significantly increased after revascularisation of the symptomatic limb. In the future, this quantitative method might serve as a non-invasive method for surveillance and therapy control of patients with peripheral arterial disease.

Key Points

• CTP imaging of the lower limb in patients with symptomatic PAD seems feasible for assessing hemodynamic differences before and after revascularisation in PAD patients.

• This quantitative method might serve as a non-invasive method, for surveillance and therapy control of patients with PAD.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-021-07692-5.

Quantitative evaluation of postintervention foot blood supply in patients with peripheral artery disease by computed tomography perfusion

OBJECTIVE

The aim of this study was to quantitatively evaluate the changes of the foot's blood supply after endovascular treatment in patients with peripheral artery disease (PAD) using foot computed tomography (CT) perfusion.

METHODS

Nineteen patients who underwent endovascular treatment for PAD between January 2018 and November 2018 were included in the study. Perfusion CT scanning was performed before and after intervention with the measurement of ankle-brachial index. Regions of interest were selected from two arteries and four different tissues per foot. Perfusion maps of blood volume, blood flow, permeability surface area product, time to peak (TTP), mean transit time (MTT), mean slope of increase (MSI), Tmax, and impulse response function (IRFt₀) were constructed and calculated by the perfusion analysis software. Wilcoxon signed rank test was performed on the eight parameter pairs of the limbs on the treated and untreated sides before and after intervention in the 19 patients.

RESULTS

Differences in blood flow, MTT, TTP, Tmax, MSI, and IRFt₀ on the treated side of the tissue perfusion group and statistical difference in blood flow, MTT, and MSI on the treated side of the arterial perfusion group were observed (all P < .05). Ankle-brachial index improved from 0.41 ± 0.11 to 0.76 ± 0.10 (P < .001). For the untreated side, TTP of the tissue perfusion group was significantly shortened (by 7.71 seconds) after surgery (P = .006), whereas there were no differences in the other parameters. In addition, no significant differences in parameters were observed on the untreated side of the arterial perfusion group. The average radiation dose per phase of perfusion scan was 0.00097 mSv. Moreover, the hyperperfusion zone in the plantar dermis and periosteum reappeared after revascularization.

CONCLUSIONS

Perfusion CT is a feasible and repeatable approach for quantifying blood supply in patients with PAD. The increase of blood flow, MSI, and MTT shortening suggest blood supply improvement after revascularization in both arterial perfusion and tissue perfusion. In addition, TTP may be a sensitive indicator of blood supply changes in tissue perfusion.

Evaluation of skeletal muscle perfusion in a canine hind limb ischemia model using CT perfusion imaging

PURPOSE

To evaluate skeletal muscle perfusion in a canine hind limb ischemia model using CT perfusion imaging (CTPI).

METHODS

Twelve beagles underwent embolization at the branch of the left deep femoral artery. The right hind limbs were used as controls. CTPI was performed immediately after embolization. The perfusion parameters of the regions of interest (ROI), including blood volume (BV), blood flow (BF), mean transit time (MTT) and permeability (PMB), were obtained in both the lateral and posterior hind limb muscle groups.

RESULTS

After embolization, the BV, BF and PMB values in the lateral muscles of the left hind limbs were significantly lower than those in the right hind limbs (P > 0.05), and the MTT was significantly prolonged (P > 0.05). The values for BV, BF, MTT and PMB in the posterior muscles of the left hind limbs were not significantly different from those in the right hind limbs (P > 0.05). The values for BV, BF and PMB in the lateral muscles of the left hind limbs were significantly lower than those in the posterior muscles of the left hind limbs (P > 0.05).

CONCLUSION

CTPI could be used to evaluate skeletal muscle perfusion in a canine model, which may have clinical relevance in lower limb ischemia and vascular reconstruction.

CT-perfusion in peripheral arterial disease - Correlation with angiographic and hemodynamic parameters

Objective

The purpose of this study was the assessment of volumetric CT-perfusion (CTP) of the lower leg musculature in patients with symptomatic peripheral arterial disease (PAD) of the lower extremities, comparing it with established angiographic and hemodynamic parameters.

Materials and methods

Thirty-five consecutive patients with symptomatic PAD of the lower extremities requiring interventional revascularization were assessed prospectively. All patients underwent a CTP scan of the lower leg, and hemodynamic and angiographic assessment. Hemodynamic parameters, specifically ankle-brachial pressure index (ABI), ankle blood pressure (ABP), peak systolic velocity (PSV), and segmental pulse oscillography (SPO) level, were determined. Lesion length and degree of collateralization were assessed by interventional angiography. CTP parameters were calculated with a perfusion software, acting on a no outflow assumption. A sequential two-compartment model was used. Differences in CTP parameters and correlations between CTP, hemodynamic and angiographic parameters were assessed with non-parametric tests.

Results

The cohort consisted of 27 subjects with an occlusion, and eight with a high-grade stenosis. The mean blood flow (BF) was 7.71 ± 2.96 ml/100ml*min^-1, mean blood volume (BV) 0.71 ± 0.33 ml/100ml, and mean mean transit time (MTT) 7.22 ± 2.66 s. BF and BV were higher in subjects with longer lesions, and BV was higher in subjects with lower ABI. Significant correlations were found between lesion length and BV (r = 0.65) and BF (r = 0.52). Significant inverse correlations were found between BV and ABI and between BV and ABP (r = -0.56, for both correlations).

Conclusions

In our study, we have shown the feasibility of CTP for the assessment of PAD. In the future, this quantitative method might serve as a non-invasive method, possibly complementing the diagnostic workup of patients with peripheral arterial disease.