Revival of monophasic contrast injection protocols: superiority of a monophasic injection protocol compared to a biphasic injection protocol in high-pitch CT angiography.

BACKGROUND: Biphasic injection protocols are frequently used because they yield homogenous contrast enhancement. We hypothesize that with faster scanners and shorter scan times, biphasic injection protocols are no longer necessary. PURPOSE: To evaluate whether a monophasic injection protocol is equivalent to a biphasic protocol in terms of contrast enhancement and homogeneity. MATERIAL AND METHODS: Repeated high-pitch CTA (pitch 3) and conventional standard-pitch computed tomography angiography (CTA) (pitch 1.2) from the cervical region to the symphysis was performed in seven beagles (11.2 ± 2.5 kg) in a cross-over study design. Arterial contrast enhancement was measured along the z-axis in the ascending, descending, and abdominal aorta and the iliac arteries. The z-axis is the longitudinal axis of the human body and at the same time the direction in which the CT table is moving. The data were analyzed using repeated measures ANOVA with a post-hoc t-test and visual assessment of the scans. RESULTS: In high-pitch CTA, monophasic injection protocols were superior to biphasic injection protocols in enhancement levels (P < 0.05) and enhancement homogeneity along the z-axis (P < 0.05). In conventional CTA, enhancement levels did not differ. Contrast homogeneity was better for biphasic protocols. CONCLUSION: High-pitch CTA monophasic injection protocols are superior to biphasic injection protocols, due to a higher and more homogeneous contrast enhancement with the same amount of contrast medium used.

A new technique of in vivo synchrotron radiation coronary microangiography in the rat.

BACKGROUND: Previously, in our laboratory, synchrotron radiation coronary microangiography (SRCA) using Langendorff-perfused rat hearts could visualize a coronary artery of 50 µm in diameter. However, in vivo rat SRCA poses the problem of compromised temporal resolution due to the rapid heart rate of rats. PURPOSE: To establish a simple method of in vivo rat SRCA with bradycardia induced by intravenous injection of adenosine triphosphate disodium hydrate (ATP). MATERIAL AND METHODS: SRCA was performed at the Photon Factory of the High Energy Accelerator Research Organization (Tsukuba, Japan). Eight male Wistar rats were anesthetized. A catheter for injecting the contrast material was inserted into the carotid artery. Temporary bradycardia was induced by an intravenous bolus injection of 5 mg of ATP, and SRCA was performed immediately thereafter. RESULTS: After ATP administration, the average heart rate decreased from 388 to 73 beats per minute. As a result, we could detect a coronary artery as small as 45 µm in diameter. CONCLUSION: Our SRCA system which has a high resolution of 9 µm per pixel could detect a coronary artery as small as 45 µm in diameter in the in vivo rat.

Hemodynamics in rat liver tumor model during retrograde-outflow isolated hepatic perfusion with aspiration from the portal vein: angiography and in vivo microscopy.

BACKGROUND: Orthograde percutaneous isolated hepatic perfusion (IHP) techniques using balloon occlusion catheters are relatively simple and facilitate repeated therapy, but they result in higher rates of leakage from the perfusion circuit into the systemic circulation. Therefore, a feasible protocol for percutaneous IHP with less leakage is required. PURPOSE: To investigate hemodynamic changes in rat liver and tumor during retrograde-outflow isolated hepatic perfusion (R-IHP) with aspiration from the portal vein (PV). MATERIAL AND METHODS: Animal experiments were approved by the Animal Experiment Ethics Committee of Lund University. Eighteen rats underwent R-IHP after laparotomy and catheterization of the PV and hepatic artery (HA). The HA, inferior vena cava (IVC), and PV were ligated, and flow through the suprahepatic IVC was controlled with a suture loop. The rats were divided into two groups to examine blood flow during R-IHP. Four rats (group 1) underwent arteriography via the HA with and without R-IHP, and 14 rats (group 2) were inoculated with tumor and examined by in vivo fluorescence microscopy of liver and tumor during R-IHP. RESULTS: In group 1, hepatic arteriography during R-IHP confirmed arterioportal communication in all four rats, with the PV acting as an outflow tract. In vivo fluorescence microscopy in group 2 showed strong enhancement of tumors, and no blood supply from the portal venules to the tumors was seen in any of the 14 rats. Blood flow in the major portion of the hepatic lobules was stopped and the percentage of enhanced area was significantly lower in the normal hepatic lobules than in the tumors (P < 0.0001). CONCLUSION: We confirmed reversal of blood flow concomitant with good perfusion of the liver tumor and with reduced perfusion of normal liver parenchyma during R-IHP.

Non-invasive quantification of anti-angiogenic therapy by contrast-enhanced MRI in experimental pancreatic cancer.

BACKGROUND: Currently, early changes of tumor vasculature after angiogenesis inhibition can only be evaluated by histopathology, a method not suitable in a clinical setting. PURPOSE: To quantify effects of different angiogenesis inhibitors on the microvasculature of orthotopically implanted pancreatic cancers by contrast-enhanced magnetic resonance imaging (MRI) in order to establish a non-invasive technique for monitoring antiangiogenic cancer treatment. MATERIAL AND METHODS: DSL-6A/C1 pancreatic cancers were implanted in the pancreas of 109 Lewis rats. Three weeks later, antiangiogenic treatment was initiated by administration of Bevacizumab (n = 38) or Suramin (n = 27) while the control group (n = 44) remained untreated. Dynamic MRI was performed 24 h, 1 week, and 4 weeks after treatment initiation. Fractional tumor plasma volume (fPV, %) and vascular permeability (K(PS), mL/min/100 cc) were calculated based on the MRI data by using a pharmacokinetic model. RESULTS: Twenty-four hours after the initial dose, a significant decline in K(PS) was observed in the Bevacizumab group compared to the control and Suramin group (0.002 ± 0.008; 0.057 ± 0.046 and 0.064 ± 0.062 (mean ± SD); P < 0.05). At 1 week, fPV was significantly smaller in Bevacizumab and Suramin treated tumors compared to control tumors (6.25 ± 2.74, 7.47 ± 3.44, and 15.10 ± 9.97, respectively; P < 0.05). Differences in tumor volumes were first observed after 4 weeks of treatment with significantly larger control tumors (4380.3 ± 1590.6 vs. 869.6 ± 717.2 and 1676.5 ± 2524.1 mm(3); P < 0.05). CONCLUSION: Dynamic MRI can quantify antiangiogenic effects on tumor microvasculature before changes in tumor volumes are detectable. Thus, this technique is a reasonable addition to morphological MRI and may be applied as an alternative to histopathology.