CT Perfusion Examinations Research Articles

Protocol modifications for CT perfusion (CTp) examinations of abdomen-pelvic tumors: Impact on radiation dose and data processing time

To evaluate the effect of CT perfusion (CTp) protocol modifications on quantitative perfusion parameters, radiation dose and data processing time. CTp datasets of 30 patients (21M:9F) with rectal (n = 24) or retroperitoneal (n = 6) tumours were studied. Standard CTp protocol included 50 sec cine-phase (0.5 sec/rotation) and delayed-phase after 70 ml contrast bolus at 5-7 ml/sec. CTp-data was sub-sampled to generate modified datasets (n = 105) with cine-phase(n = 15) alone, varying cine-phase duration (20-40 sec, n = 45) and varying temporal sampling-interval (1-3 sec, n = 45). The estimated CTp parameters (BF,BV,MTT&PS) and radiation dose of standard CTp served as reference for comparison. CTp with 50 sec cine-phase showed moderate to high correlation with standard CTp for BF&MTT (r = 0.96&0.85) and low correlation for BV (0.75, p = 0.04). Limiting cine-phase duration to 30 sec demonstrated comparable results for BF&MTT, while considerable variation in CTp values existed at 20 sec. There was moderate-to-high correlation of CTp parameters with sampling interval of 1&2 sec (r = 0.83-0.97, p > 0.05), while at 3 sec only BF showed high correlation (r = 0.96, p = 0.05). Increasing sampling interval (47-60%) and reducing cine-phase duration substantially reduced dose(30.8-65%) which paralleled reduced data processing time (3-10 min). Limiting CTp cine-phase to 30 sec results in comparable BF&MTT values and increasing cine-phase sampling interval to 2 sec provides good correlation for all CTp parameters with substantial dose reduction and improved computational efficiency.

Utilization guidelines for reducing radiation exposure in the evaluation of aneurysmal subarachnoid hemorrhage: A practice quality improvement project.

The purpose of this study was to reduce the cumulative radiation exposure from CT of patients with aneurysmal subarachnoid hemorrhage. Baseline data on 30 patients with aneurysmal subarachnoid hemorrhage were collected retrospectively for all CT examinations of the head performed throughout the hospital course. Radiation exposure estimates were obtained by recording dose-length products for each examination. As a departmental practice quality improvement project, an imaging protocol was implemented that included utilization guidelines to reduce radiation exposure in CTA and CT perfusion examinations performed to detect vasospasm in patients with aneurysmal subarachnoid hemorrhage. Ten months after implementation of this protocol, data on 30 additional patients were analyzed. Means, medians, and SD estimates were compared for cumulative radiation exposure and absolute numbers of each examination. Sixty patients were included in the study: 30 patients at baseline and 30 patients after implementation of the quality improvement plan. These patients underwent 435 CT examinations: 248 examinations at baseline and 187 examinations with the new protocol. With the new algorithm, the mean number of CT examinations per patient was 5.8 compared with 7.8 at baseline, representing a decrease of 25.6%. The number of CT perfusion examinations per patient decreased 32.1%. Overall, there was a 12.1% decrease in cumulative radiation exposure (p > 0.05). With the structured imaging algorithm, the cumulative radiation exposure and number of CT examinations of the head decreased among patients with aneurysmal subarachnoid hemorrhage because utilization guidelines defined the appropriate imaging time points for detection of vasospasm. Application of these methods to other patient populations with high use of CT may reduce cumulative radiation exposure while the clinical benefits of imaging are maintained.

P-022 Treating symptomatic intracranial atherosclerosis with the balloon expandable Pharos Vitesse neurovascular stent: initial experience

PurposeTo describe our early experience with the balloon expandable Pharos Vitesse stent for symptomatic, high grade intracranial stenosis.Materials and methodsOur center has enrolled five patients to date in the VISSIT...

SU-GG-I-37: Reducing Eye Lens Dose during Brain Perfusion CT Examinations by Moving the Scan Location or Tilting the Gantry Angle

Purpose: Brain perfusion CT studies may result in radiation doses to the eye lens because of repeated scans that may in some cases be high enough to cause deterministic effects, such as cataracts. The purpose of this study is to investigate the eye lens dose from brain perfusion CT studies, and the dose reduction achieved by clinically practical approaches, such as moving the x-ray beam away from the eye lens or tilting the gantry angle. Method and Materials: Eye lens doses were estimated using the Monte Carlo method with: (a) a detailed voxelized patient model including a model of the lens of the eye; and (b) detailed CT source models of a Siemens Sensation 64 scanner using the widest collimation (28.8mm) and 120 kVp tube voltage. Simulated brain perfusion axial scans were performed at various scan locations from 5.5cm above the eye lens to 5.5cm below the eye lens with 0.5cm intervals to investigate the scatter contribution to the eye lens dose. For the scan location where the eye lens is completely in the beam, the gantry was tilted at 5, 10, 15, 20, 25 and 30 degrees to study the dose reduction. Results: Eye lens dose drops dramatically as the scan location moves away. When the lenses are just outside the primary x-ray beam, the dose is 17% of the maximum dose when they are completely in the beam. Tilting the gantry angle by 15 degree reduces the eye lens dose by 87%. Conclusion: The eye lens dose from CT perfusion examinations can be reduced by moving the beam away from the eyes since the scatter component is fairly small. When the examination has to be performed right over the location of the eyes, tilting the gantry angle is another effective method to reduce the eye lens dose.

Gastric adenocarcinoma: can perfusion CT help to noninvasively evaluate tumor angiogenesis?

Perfusion CT is an attractive technique to assess tumor vascularity, and no studies have addressed the relationship between CT perfusion imaging and gastric tumor angiogenesis with volume-based technique. This study aims to assess the correlation between perfusion CT parameters using a volume-based technique and immunohistochemical markers of angiogenesis in gastric adenocarcinoma. 37 patients with gastric adenocarcinoma who completed whole tumor CT perfusion examination with volume-based technique were studied. Post surgical specimens were stained using a polyclonal antibody to VEGF and CD34. Perfusion measurements were correlated with microvessel density (MVD) and VEGF by using Pearson or Spearman rank correlation analysis, in which a P value < 0.05 was considered statistically significant. The mean MVD of all 37 tumors was 108.9 ± 38.2 vessels/0.723 mm². 70.3% (26 of 37) of tumors expressed VEGF positively. MVD of gastric adenocarcinoma was significantly correlated with blood volume (the Pearson correlation coefficient being 0.420, P = 0.001). No correlations were found between VEGF expression and perfusion CT parameters. There were no significant differences in the parameters between the high and low MVD groups, and between the positive and negative VEGF groups. Blood volume was significantly correlated with MVD. It could reflect the angiogenesis in gastric adenocarcinoma.

Feasibility of Superficial Temporal Artery as the Input Artery for Cerebral Perfusion CT

The purpose of this study was to determine whether the superficial temporal artery as a surrogate arterial input function, compared with the anterior cerebral artery as the arterial input function, generates accurate perfusion CT maps with significant correlates for cerebral blood flow, cerebral blood volume, and mean transit time. One hundred perfusion CT examinations performed on 90 patients (51 women and girls, 39 men and boys) were retrospectively reviewed and postprocessed by one investigator using CT perfusion software at a workstation. Color-coded cerebral blood flow, cerebral blood volume, and mean transit time maps were constructed with the superficial temporal artery as a surrogate arterial input function and the anterior cerebral artery as the arterial input function. The effect of input artery choice on mean cerebral blood flow, cerebral blood volume, and mean transit time values in six regions of interest (one region of interest in each anterior cerebral artery, middle cerebral artery, and posterior cerebral artery territory) was assessed. All graphs of correlation between the anterior cerebral artery as the arterial input function and the superficial temporal artery as a surrogate arterial input function produced significant results (p < 0.0001). Excellent correlation existed between the cerebral blood flow (r = 0.96 [Pearson correlation coefficient]; rho(c) = 0.96 [concordance correlation coefficient]), cerebral blood volume (r = 0.97; rho(c) = 0.97), and mean transit time (r = 0.97; rho(c) = 0.97) values obtained with the anterior cerebral artery and the values obtained with the superficial temporal artery. Linear regression lines produced strong agreement between use of the anterior cerebral artery and use of the superficial temporal artery (cerebral blood flow, y = 1.03x + 0.65; cerebral blood volume, y = 1.05x - 0.09; mean transit time, y = 0.92x + 0.21). The preliminary results show that using an extracranial vessel such as the superficial temporal artery as a surrogate input artery can generate perfusion maps comparable with those generated with an intracranial vessel such as the anterior cerebral artery. This knowledge can be useful if the proximal intracranial vessels typically used for arterial input are not visible owing to diffuse disease, such as diffuse vasospasm and atherosclerosis, or are not included in the field of view of perfusion CT.

Intracranial CT angiography obtained from a cerebral CT perfusion examination

CT perfusion (CTP) examinations of the brain are performed increasingly for the evaluation of cerebral blood flow in patients with stroke and vasospasm after subarachnoid hemorrhage. Of the same patient often also a CT angiography (CTA) examination is performed. This study investigates the possibility to obtain CTA images from the CTP examination, thereby possibly obviating the CTA examination. This would save the patient exposure to radiation, contrast, and time. Each CTP frame is a CTA image with a varying amount of contrast enhancement and with high noise. To improve the contrast-to-noise ratio (CNR) we combined all 3D images into one 3D image after registration to correct for patient motion between time frames. Image combination consists of weighted averaging in which the weighting factor of each frame is proportional to the arterial contrast. It can be shown that the arterial CNR is maximized in this procedure. An additional advantage of the use of the time series of CTP images is that automatic differentiation between arteries and veins is possible. This feature was used to mask veins in the resulting 3D images to enhance visibility of arteries in maximum intensity projection (MIP) images. With a Philips Brilliance 64 CT scanner (64 x 0.625 mm) CTP examinations of eight patients were performed on 80 mm of brain using the toggling table technique. The CTP examination consisted of a time series of 15 3D images (2 x 64 x 0.625 mm; 80 kV; 150 mAs each) with an interval of 4 s. The authors measured the CNR in images obtained with weighted averaging, images obtained with plain averaging, and images with maximal arterial enhancement. The authors also compared CNR and quality of the images with that of regular CTA examinations and examined the effectiveness of automatic vein masking in MIP images. The CNR of the weighted averaged images is, on the average, 1.73 times the CNR of an image at maximal arterial enhancement in the CTP series, where the use of plain averaging increases the CNR only with a factor of 1.49. The quality of the weighted averaged images approaches that of CTA images, although in the present study the image quality of CTA was not quite reached. The automatic masking of veins is effective and only small remnants of veins were sometimes present in the masked images. Weighted averaging makes it possible to create CTA images from a CTP examination with a CNR considerably higher than that of images with maximal arterial enhancement. The quality of the resulting images approaches that of CTA images and offers the additional advantages to automatically differentiate between arteries and veins.

Evaluation of Portal Hypertension: A Comparison of the Use of Liver Perfusion CT with Wedge Hepatic venous Pressure and Hepatic venous Pressure Gradient

Purpose: We compared the hepatic perfusion indices obtained using hepatic perfusion CT with the wedge hepatic venous pressure (WHVP) and hepatic venous pressure gradient (HVPG) to determine the efficacy of the use of liver perfusion CT for the evaluation of portal hypertension. Materials and Methods: Thirty-five patients with liver cirrhosis underwent hepatic vein catheterization to measure WHVP and HVPG and underwent a liver perfusion CT examination. Arterial perfusion, portal perfusion, total perfusion and the hepatic perfusion index (HPI) were calculated by the methods described by Miles and Blomley. The overall correlation coefficients (r) between the perfusion indices and WHVP and HVPG were calculated. An additional correlation coefficient of 23 alcoholic cirrhosis patients was calculated. Results: Using Blomley’s equation, HPI had a positive correlation with WHVP (r = .471; p

Quantitative Tissue Blood Flow Measurement of the Liver Parenchyma: Comparison Between Xenon CT and Perfusion CT

The purpose of this study was to compare measurements of hepatic tissue blood flow (TBF) calculated by xenon and perfusion CT. Seven patients with normal liver and eight with chronic liver disease underwent both xenon and perfusion CT. During xenon CT examinations, serial abdominal CT scans were obtained every minute before and during 4 min of nonradioactive 25% (v/v) xenon gas inhalation and 5 min of administration of oxygen-rich air. Hepatic arterial and portal venous TBF were measured separately with a special imaging system using the Kety-Schmidt expression based on the Fick principle (AZ-7000W; Anzai Medical Co.). The hepatic arterial fraction (HAF) was calculated as follows: [hepatic arterial TBF/(hepatic arterial TBF + portal venous TBF)]. During perfusion CT examinations, total hepatic TBF and HAF were also calculated from the enhanced CT cine image data on a workstation using a commercially available software package based on a deconvolution algorithm (CT Perfusion 3 GE Healthcare, USA). Total hepatic TBF measured by xenon and perfusion CT was 82.9+/-15 and 82.8+/-18 ml/min/100 g, respectively. The measured values by the two techniques showed a significant correlation (R (2)= 0.657, P < 0.05). HAF measured by xenon and perfusion CT was 26.6+/-11 and 21.8+/-13%, respectively. The measured values by the two techniques also showed a significant correlation (R (2)= 0.869, P < 0.05). We conclude that there was a good correlation between hepatic TBF quantified by xenon CT and perfusion CT.