Blood-brain barrier and blood volume imaging of cerebral glioma using functional CT: a pictorial review

Role of immature microvessels in assessing the relationship between CT perfusion characteristics and differentiation grade in lung cancer

BACKGROUND AND AIMS

We undertook this study to investigate the association between CT perfusion characteristics and differentiation grade in lung cancer, as well as the pathological basis of this association.

METHODS

Seventy three patients received CT perfusion scan and pathological biopsy, and 30 of them were available for comparison. In these 30 patients, the region detected with pathological biopsy was consistent with the region of interest of CT perfusion. We compared the CT perfusion parameters [blood volume (BV), blood flow (BF), and peak enhancement intensity (PEI)] of these patients with their differentiation grade of lung cancer and microvessel count, which includes microvessel density (MVD) and maturity.

RESULTS

The lower the grade of differentiation of the nodules, the more drastically perfusion parameters decreased. BF was best correlated with differentiation grade (r = -0.845, p = 0.000), compared to BV and PEI (r = -0.674, -0.438, p = 0.000, 0.015, respectively). Poorly differentiated lung cancer showed significantly higher density of immature microvessels than that of highly differentiated lung cancer (p = 0.001). There was a correlation between the differentiation grade and the density of immature microvessels (r = 0.669, p = 0.000), but there was no significant correlation with MVD and the density of mature microvessel (r = 0.345, 0.269, p = 0.062, 0.150, respectively). The density of immature microvessels still increased with declining BF value in the nodules when the grade of differentiation of lung cancer was under control (r = -0.748, p = 0.000).

CONCLUSIONS

CT perfusion characteristics are helpful to differentiate lung cancer differentiation, pathologically basing on the density of immature microvessels rather than MVD.

Spinal cord blood flow and blood vessel permeability measured by dynamic computed tomography imaging in rats after localized delivery of fibroblast growth factor

Following spinal cord injury, profound vascular changes lead to ischemia and hypoxia of spinal cord tissue. Since fibroblast growth factor 2 (FGF2) has angiogenic effects, its delivery to the injured spinal cord may attenuate the tissue damage associated with ischemia. To limit systemic mitogenic effects, FGF2 was delivered to the spinal cord via a gel of hyaluronan and methylcellulose (HAMC) injected into the intrathecal space, and compared to controls receiving HAMC alone and artificial cerebrospinal fluid (aCSF) alone. Dynamic perfusion computed tomography (CT) was employed for the first time in small animals to serially measure blood flow and permeability in the injured and uninjured spinal cord. Spinal cord blood flow (SCBF) and permeability-surface area (PS) measurements were obtained near the injury epicenter, and at two regions rostral to the epicenter in animals that received a 26-g clip compression injury. As predicted, SCBF measurements decreased and PS increased after injury. FGF2 delivered via HAMC after injury restored SCBF towards pre-injury values in all regions, and increased blood flow rates at 7 days post-injury compared to pre-injury measurements. PS was stabilized at regions rostral to the epicenter of injury when FGF2 was delivered with HAMC, with significantly lower values than aCSF controls at 7 days in the region farthest from the epicenter. Laminin staining for blood vessels showed a qualitative increase in vessel density after 7 days when FGF2 was locally delivered. Additionally, permeability stains showed that FGF2 moderately decreased permeability at 7 days post-injury. These data demonstrate that localized delivery of FGF2 improves spinal cord hemodynamics following injury, and that perfusion CT is an important technique to serially measure these parameters in small animal models of spinal cord injury.

Detecting metastasis of lymph nodes and predicting aggressiveness in patients with breast carcinomas

OBJECTIVE

The purpose of this study was to evaluate the contrast-enhanced ultrasonographic (CEUS) characteristics of metastatic lymph nodes (LNs) and to determine the correlation of CEUS parameters with the tumor aggressiveness in patients with breast cancer.

METHODS

Real-time gray scale CEUS of axillary LNs was preoperatively performed in 51 consecutive patients with breast carcinoma who were scheduled for axillary lymph node dissection. The CEUS characteristics assessed by a direct visualization method and quantification software were compared with pathologic findings. Expression of human epidermal growth factor receptor 2 (HER-2/neu) in the primary tumor was detected by immunohistochemical analysis. Correlation analysis of CEUS parameters with HER-2/neu expression and the LN stage was performed.

RESULTS

Of the LNs examined, 27 were metastatic, and 25 were diagnosed as reactive hyperplasia. Lymph nodes with metastasis were characterized by centripetal progress (66.7%) and a heterogeneous pattern (55.6%) or no or scarce perfusion (25.9%). However, LNs with nonmetastases were characterized by with centrifugal enhancement (56.0%) and a homogeneous pattern (80.0%). The difference between the hyperintense and hypointense regions was higher in metastatic LNs than nonmetastatic ones (P < .001). No significant differences were found in the arrival time, time to peak intensity, and peak intensity between the two groups. A histopathologic diagnosis could be predicted with sensitivity, specificity, and accuracy of 92.6%, 76.0%, and 84.6% respectively, by a standardized difference between maximum and minimum signal intensity (SI(max)-SI(min)) value of 28. Human epidermal growth factor receptor 2 expression and the LN histopathologic stage were significantly associated with the SI(max)-SI(min). In metastatic LNs, the relationship between the diagnostic sensitivity of CEUS and the transverse diameter of LNs remained statistically significant (P < .05).

CONCLUSIONS

Noninvasive CEUS can play a role in discriminating metastatic from nonmetastatic LNs and predicting the aggressiveness in patients with breast cancer.

Use of permeability surface area-product to differentiate intracranial tumours from abscess

Background and Purpose

Clinical and radiological findings of intracranial abscesses may mimic the findings of brain tumours and vice versa. However, the discrimination is of great clinical importance in planning treatment and in following prognosis and response to therapy. This study evaluates the Computed Tomography (CT) perfusion parameters, especially the permeability index, with the aim of evaluating the usefulness of dynamic CT perfusion imaging as an alternative tool to differentiate necrotic brain tumours and intracerebral abscesses.

Materials and Methods

A total of 21 patients underwent perfusion CT study and were divided into 2 groups: Group 1, patients with necrotic brain tumours (n=13); and Group 2, patients with cerebral abscesses (n=8). The mean perfusion parameters were obtained from the enhancing part of the lesion. The relative ratios were then calculated by using the results from mirrored regions within the contralateral hemisphere as reference.

Results

The results of this study showed that there was significant difference in the relative permeability surface values between necrotic brain tumours and cerebral abscesses (p=0.005). By applying the ROC curve, a value of 25.1 for rPS was found to be the best estimate to distinguish necrotic brain tumours from cerebral abscesses with a specificity of 88 % and sensitivity of 70 %.

Conclusion

CT perfusion, especially permeability surface, may allow for better differentiation of cerebral abscesses from brain tumours, making it a strong additional imaging modality in the early diagnosis of these two entities.

Imaging angiogenesis

There is a need for direct imaging of effects on tumor vasculature in assessment of response to antiangiogenic drugs and vascular disrupting agents. Imaging tumor vasculature depends on differences in permeability of vasculature of tumor and normal tissue, which cause changes in penetration of contrast agents. Angiogenesis imaging may be defined in terms of measurement of tumor perfusion and direct imaging of the molecules involved in angiogenesis. In addition, assessment of tumor hypoxia will give an indication of tumor vasculature. The range of imaging techniques available for these processes includes positron emission tomography (PET), dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), perfusion computed tomography (CT), and ultrasound (US).

High-concentration contrast media in neurological multidetector-row CT applications: implications for improved patient management in neurology and neurosurgery

Dynamic CT scanning after intravenous injection of iodine contrast medium (CM) was proposed in the very early days of CT. The goal was to characterize tissue by extracting information from the temporal course of enhancement. In the early 1980s, modeling algorithms were already described in the literature for the quantitative calculation of cerebral blood flow (CBF). However, cerebral applications suffered from the insufficient temporal resolution available at that time and the central nervous system was already seen primarily as an MRI domain. The renaissance of dynamic CT in neurological applications came in the middle of the 1990s with the introduction of thrombolytic therapy in acute stroke. With CT being the primary imaging modality, getting additional hemodynamic information from the same device without having to move the patient appeared attractive. Multimodal CT protocols allow a comprehensive diagnosis of the emergency stroke patient in less than 15 minutes by combining nonenhanced CT (NECT), perfusion CT (PCT) and CT angiography (CTA). Dynamic PCT can also render important information in patients with intraaxial brain tumors, allowing differentiation not only between lymphoma and glioma but also between low-grade and high-grade glioma by quantifying local cerebral blood volume (CBV) and permeability of the blood-brain barrier (BBB). However, even if a shorter imaging time permits a reduction in volume of CM, adequate total iodine levels must be preserved for dynamic CT applications. Increased concentrations of iodine are therefore helpful to obtain adequate total iodine levels for imaging.

Functional imaging in clinical oncology: magnetic resonance imaging- and computerised tomography-based techniques

Over recent years, advances in cellular biology, molecular biology and genetics have led to a leap forward in our understanding of the biological basis of cancer. Some of these developments have revealed processes and targets that can be visualised and measured by new functional imaging techniques. The resulting images have the potential to improve cancer staging, prognosis and risk assessment, guide radiotherapy planning, direct treatment schedules, improve response assessment and provide new end points for clinical trials. In this review, we have outlined the magnetic resonance imaging- and computerised tomography-based functional techniques and provide evidence for their use.

Perfusion CT for the assessment of tumour vascularity: which protocol?

Perfusion CT is a technique that can be readily incorporated into the existing CT protocols that continue to provide the mainstay for anatomical imaging in oncology to provide an in vivo marker of tumour angiogenesis. By capturing physiological information reflecting the tumour vasculature, perfusion CT can be useful for diagnosis, risk-stratification and therapeutic monitoring. However, a wide range of perfusion CT techniques have evolved and the various commercial implementations advocate different acquisition protocols and processing methods. Acquisition choices include first pass studies or delayed imaging, temporal resolution versus image noise, and single location sequences or multiple spiral acquisitions. Data processing may be semi-quantitative or, using either compartmental analysis or deconvolution, produce results that are quantified in absolute physiological terms such as perfusion, blood volume and permeability. This article discusses the advantages and disadvantages of the more common CT perfusion protocols and offers proposals that could allow for easier comparison between studies employing different techniques.

Functional CT imaging in oncology

The two-compartment pharmacokinetics exhibited by iodinated contrast media makes these agents well suited to the study of tumour angiogenesis in which new vessels are not only produced in greater number but also are abnormally permeable to circulating molecules. The temporal changes in contrast enhancement of tumours on CT have been shown to correlate with histopathological assessments of angiogenesis with the intravascular and extravascular phases of contrast enhancement reflecting microvessel density and vascular permeability, respectively. By quantifying tumour contrast enhancement to capture physiological information about the vascular system, functional CT can provide a useful adjunct to the anatomical information afforded by MDCT in oncology, aiding with tumour diagnosis, risk stratification and therapy monitoring. By simultaneously assessing tumour vascularity and metabolic demand, the broader expansion of integrated MDCT/PET imaging will support highly sophisticated assessments of tumour biology within a single examination.

Functional computed tomography in oncology

Functional Computed Tomography (CT) describes the use of existing technologies and conventional contrast agents to capture physiological parameters that reflect the vasculature within tumours and other tissues. The technique is readily incorporated into routine conventional CT examinations and, in tumours, the physiological parameters obtained provide an in-vivo marker of angiogenesis. As well as providing a research tool, functional CT has clinical applications in tumour diagnosis, staging, risk stratification and therapy monitoring, including the characterisation of pulmonary nodules, detection of occult hepatic metastases, grading of cerebral glioma and monitoring of anti-angiogenesis drugs. With the recent commercial availability of appropriate software and the development of multislice CT systems, functional CT is poised to make a significant impact upon the imaging of patients with cancer.

Tumour angiogenesis and its relation to contrast enhancement on computed tomography: a review

Angiogenesis describes the formation of new blood vessels within tumours. The process is essential for tumour growth and metastasis. The development of new vessels leads to physiological changes, specifically increased perfusion, blood volume and capillary permeability, that alter contrast enhancement during computed tomography (CT). Functional CT techniques that quantify these physiological changes can provide greater insight into how angiogenesis alters contrast enhancement in routine practice and also serve as diagnostic tools in their own right. The functional information obtained can aid with tissue characterisation, such as type or grade of tumour, improve the detection of hepatic metastases, produce clearer delineation of tumours with benefits for radiotherapy planning and biopsy, and provide prognostic information. By providing a marker for tumour angiogenesis, quantitative contrast enhanced CT can improve the diagnostic assessment of patients with cancer.