Scan Delay Time Research Articles

Variation of Attenuation Value of Pancreas at Dual Phase MDCT: Comparison of the Bolus-tracking Technique vs. the Fixed Scan Delay Protocol

Purpose: To clarify the difference between the bolus-tracking technique and a fixed scan delay protocol in the achievement of the optimal pancreatic phase of the pancreas with MDCT. Materials and Methods: 526 patients underwent pancreatic and portal venous phase imaging of the pancreas using 16-channel MDCT. All the examinations were randomized into either scanning using a bolus-tracking technique with a scan delay of 20s after the aorta was enhanced > 100 HU (groups 1 and 2) or scanning with a scan delay of 38 s from the beginning of the injection (groups 3 and 4). A contrast material of 300 mgI/mL (groups 1 and 3) or 370 mgI/mL (groups 2 and 4) at an injection speed of 3 mL/sec was injected at 2 mL/kg body weight. The pancreatic CT attenuation values were compared. Results: The scan delay times of the pancreatic phase in groups 1 and 2 were 38±3.8s and 37.4±3.4s, respectively. At the pancreatic phase, the pancreatic attenuation values of groups 1 and 2 were slightly higher than those of groups 3 and 4 (115.5±15.4 vs 111.7±15.1HU; p=0.093, 128.3±17.1 vs 119±17.1HU; p=0.003). There was no significant difference between groups at the portal venous phase. Conclusion: The use of a bolus-tracking technique in the optimal pancreatic phase of pancreatic CT does not significantly improve the pancreatic enhancement but does at higher iodine concentrations.

Optimal Delay Time for the Hepatic Parenchymal Enhancement at the Multidetector CT Examination

The objective of this study was to determine the optimal scan delay time after hepatic parenchymal enhancement using a 16-channel multidetector row helical CT (MDCT) scanner. Two hundred fifty-five consecutive patients underwent biphasic CT scans using a 16-channel MDCT. In group A (n = 125), two hepatic venous phase scans (HVP1 and HVP2) were obtained at 40 and 60 seconds, after 100-HU threshold time (T100HU) in the abdominal aorta. In group B (n = 130), HVP1 and HVP2 scans were obtained 50 and 70 seconds after T100HU. Both groups were divided into subgroups that were given different contrast media. Groups A1 and B1 received a contrast medium of 300 mgI/mL; groups A2 and B2 received a contrast medium of 370 mgI/mL. Each patient was injected with contrast medium at a dose of 2 mL/kg at a rate adjusted to the patient's body weight with a constant injection duration of 47 seconds. The attenuation values (HU) for the liver, portal vein, hepatic vein, and aorta were measured. The average HU was compared between the groups. Hepatic enhancement in the images obtained at 50 and 60 seconds after T100HU was greater (P < 0.05) than in images obtained at 40 and 70 seconds. These results were obtained with both contrast media. A few patients showed greater enhancement at a 40 seconds or 70 seconds. Hepatic enhancement was significantly greater in all scans using a contrast medium dose of 370 mgI/mL compared with the 300-mgI/mL dose (P < 0.05). Independent of the concentration of contrast medium, scan delays of 50 to 60 seconds after T100HU may provide optimal hepatic enhancement.

Variation of the Time to Aortic Enhancement of Fixed-Duration Versus Fixed-Rate Injection Protocols

The objective of the study was to clarify whether a fixed-duration injection protocol is useful in determining the optimal scan delay time without the need for a bolus-tracking technique. Three hundred eighteen patients underwent a helical CT examination using a bolus-tracking technique. All the examinations were performed after administering a nonionic contrast medium (300 or 370 mg I/mL; 2 mL/kg of body weight for patients weighing < or = 75 kg, 150 mL for those weighing > 75 kg). The patients were assigned to one of three groups according to the injection protocol. The injection rate was alternated to 3 or 4 mL/sec in group 1. The injection duration was 38 or 47 sec in groups 2 and 3, respectively. The aortic arrival time and the 100-H threshold time in each patient were measured. The mean values and the variations in the aortic arrival time and 100-H threshold time according to the injection protocols and the contrast media were compared. The mean variations (+/- SD) of aortic arrival times and 100-H thresholds in group 2 (aortic arrival time = 16.1 +/- 2.7 sec, 100-H threshold time = 19.6 +/- 2.9 sec) were smaller than in groups 1 (16.3 +/- 3.0 sec and 19.9 +/- 3.7 sec, respectively) and 3 (16.8 +/- 3.5 sec and 20.4 +/- 4.1 sec, respectively). However, the range of aortic arrival times and 100-H threshold times was more than 10 sec for all groups. The mean aortic arrival time and 100-H threshold time for all patients were 16.5 and 20.0 sec, respectively, and did not vary significantly with the injection protocol and concentration of contrast medium. The individual variations of the aortic arrival and 100-H threshold times can be reduced using a fixed-duration injection technique, but there are still substantial variations. Therefore, a bolus-tracking technique is recommended for optimal timing of arterial phase scanning.

3D contrast-enhanced MR angiography of the abdominal aorta and its distal branches: Interobserver agreement of radiologists in a routine examination 1

To evaluate the quality of images of the aorta and visceral arteries made at a high level of spatial resolution with thin slices and an optimized acquisition time by three-dimensional contrast-enhanced magnetic resonance angiography (3D CE-MRA). 3D CE-MRA with a 1.4-mm slice thickness and 512-pixel base matrix was done on 62 consecutive patients with a 1.5-T magnetic resonance imaging MRI unit. A bolus test with a power injector was used to calculate the optimal scan delay time. For quantitative evaluation, the signal-to-noise ratio (SNR) was measured in 3 regions of interest. Qualitative image analysis was evaluated independently by two radiologists and graded on a scale of 0-3. Separate analyses were done for the aorta and distal visceral arterial branches. The means SNR values were respectively 56.2 +/- 15.2 (mean +/- SD) for the aorta, 59.2 +/- 15.1 for the celiac trunk, and 57 +/- 15.2 for the superior mesenteric artery, with a homogeneous distribution (P = .99). Consistent enhancement was confirmed by the lack of statistically significant differences between the SNR values. The average score for vessel visualization on source images ranged from good to excellent for different segments. After post-processing of images, the average score for distal arterial segments was significantly improved. The overall agreement between the 2 reviewers in the visualization of definite artery segments was excellent (k = .91). 3D CE-MRA with a 512-pixel base matrix and thin slices can be applied in a reproducible way with excellent depiction and delineation of small vessels. Such a protocol could be used routinely.

Multislice spiral CT in pancreas examination: optimal multi-phase enhanced scan delay time

目的 确定合理的多层螺旋CT(MSCT)胰腺检查多期增强扫描延迟时间.方法随机选择61例无胰腺疾病患者,分为2个步骤研究:(1)21例行胰腺同层动态增强扫描,对比剂总量为120 ml,注射流率为5 ml/s,分别测定胰周主动脉、胰周门静脉、胰腺实质及肝脏实质在增强后不同时间点的CT值,确立最佳的多期(动脉期、胰腺期及肝脏期)增强扫描延迟时间.(2)40例行MSCT胰腺移床式、多期动态增强扫描,对比剂总量和注射流率同上,分别评价动脉期与胰腺期胰周血管的显示率及显示程度.结果 (1)同层动态扫描结果提示,胰周主动脉强化到达峰值平均时间为30 s(延迟时间20 s时胰周主动脉CT值已达200 HU左右),胰腺实质强化到达峰值平均时间为40 s,胰周门静脉强化到达峰值平均时间为45 s,肝脏实质强化到达峰值平均时间为60 s(60～80 s,基本处于一平台期);(2)胰周大动脉于动脉期显示率为100%,显示程度平均评分为2.93～2.95,胰周其他主要动脉期显示率为78%～98%,显示程度平均评分为0.85～2.63;胰周大静脉于胰腺期显示率为100%,显示程度平均评分为2.80～2.88,胰周其他主要静脉胰腺期显示率为90%～100%,显示程度平均评分为1.08～1.90.结论 MSCT行胰腺检查,须进行三期增强扫描,推荐延迟时间分别为:动脉期为20 s、胰腺期为45 s、肝脏期为80 s。

Hepatocellular carcinoma: assessment of vascularity with single-level dynamic ultrasonography during the arterial phase.

To evaluate the hemodynamic features of hepatocellular carcinoma on single-level dynamic ultrasonography during the arterial phase. Twenty-two hepatocellular carcinomas were examined by single-level dynamic ultrasonography with high transmit intensity and SH U 508A. The scans were performed for 40 seconds with a 1-second interval between each ultrasound transmission and with individual optimization of the scan delay time. The times of initiation of enhancement for both the hepatic artery and the tumor and the time of maximal enhancement for the tumor were recorded, and the mean echo values at every second for the tumor and hepatic parenchyma were measured. Twelve tumors showed hyperechoic enhancement compared with hepatic parenchyma throughout the scans. The other 10 showed hyperechoic enhancement during some segments (range, 8-34 seconds) and either isoechoic (n = 5) or hypoechoic (n = 5) enhancement during the remaining parts; the hyperechoic segments were often short (< 20 seconds, 14%). Although the times for initiation of enhancement for the hepatic artery and hepatocellular carcinoma and the time of maximal enhancement for the tumor varied, the tumor usually initiated enhancement immediately after the hepatic artery (r = 0.986; P = .000001). The interval between the time of initiation of enhancement for the tumor or hepatic artery and that of maximal enhancement for the tumor was significantly correlated with the tumor size (r = 0.700; P = .008; and r = 0.780; P = .002). With individual optimization of the scan delay time, single-level dynamic ultrasonography is useful for depicting the hypervascularity of hepatocellular carcinoma during the arterial phase.

Feasibility of electron beam tomography in diagnosis of congenital heart disease: comparison with echocardiography

Objective: To evaluate the feasibility of electron beam tomography (EBT) for morphological assessment of congenital heart disease. Materials and methods: Sixteen subjects were examined by EBT, transthoracic echocardiography, cardiac cine angiography and surgery. EBT scan was performed using single slice continuous volume mode to acquire high-resolution static image. Double dose contrast medium was injected by bolus technique after measuring scan delay time and calculation of proper injection rate. The results of EBT and echocardiography were compared based on the results of cardiac cine angiography and surgical findings. All anomalous components were evaluated in all subjects and grouped according to major cardiac structures. Statistical analysis was performed to compare two modalities’ ability to evaluate the anomalies of major structures. Results: EBT was more sensitive to evaluate the anomalies of systemic vessels, pulmonary vessels and small systemic arteries such as coronary artery. EBT was less sensitive to identify the abnormality of cardiac valves such as valvular regurgitation. There was no difference of sensitivity in evaluation of cardiac chambers and septa between the two modalities. Conclusion: EBT assisted by transthoracic echocardiography is excellent noninvasive modality to diagnose congenital heart disease.

Optimizing of gadolinium-enhanced MR angiography by manipulation of acquisition and scan delay times

An optimized protocol for achieving high-quality contrast-enhanced MR angiography (CE MRA) was designed and evaluated. Time-intensity curves of the test bolus and main bolus were compared in 11 volunteers. To identify the acquisition zone sensitive to venous overprojection, sequential filling phantoms which consisted of 12 test tubes were developed and scanned. Using the parameters of the time-intensity curve which were consistent between the test and main boluses and the parameters of the sensitive acquisition zone in the pulse sequences, the protocol for calculation of scan delay time and acquisition time was optimized. The new protocol was verified by comparison of lower extremity CE MRAs acquired by traditional (scan delay time = peak enhancement time minus injection duration/2 + acquisition time/2; n = 12) and new (n = 23) protocols. The arterial and venous enhancing times of the time-intensity curves of the test and main boluses were statistically consistent (p < 0.01). The length of the sensitive acquisition zone was one-half the acquisition duration. With the parameters identified in the time-intensity curve and pulse sequence analyses, a new protocol was developed. For validation, the new protocol was able to study the smaller arteries such as the distal tibial arteries and branches of the femoral and iliac arteries (p < 0.01). Using the optimized protocol, higher-quality images were obtained than those acquired by traditional methods.

CONTRAST-ENHANCED THORACIC 3D-MR ANGIOGRAPHY IN INFANTS AND CHILDREN

Purpose: To optimise breath-hold contrast-enhanced MR angiography (MRA) in infants and children with suspected congenital heart or thoracic vessel malformation. Material and Methods: Thirty-nine children (median age 1 year) were examined, using five different ultrafast MRA sequences with a TR between 3.2 and 5.0 ms and the contrast agent meglumine gadoterate. A test injection was used to determine contrast travel time. Different parameters for contrast injection were evaluated. Signal-to-noise ratio (SNR) measurements were performed and image quality and injection timing were evaluated. Results: MRA was successful in all patients and image quality was considered very good in 52%. Adequate SNR was achieved with no significant differences between the MR sequences. SNR decreased only 25-30% between subsequent scans. The mean contrast dose was 0.23 mmol/kg. The mean scan time was 12.5±3.8 s; the shorter scan times made dynamic examinations possible with high temporal resolution. Highest spatial resolution was obtained with TR 4.6/5.0 sequences. Conclusion: A contrast dose of 0.2 mmol/kg b.w. is recommended with an injection rate of 0.5 to 1.2 ml/s, depending on patient size and scan time. The scan delay time should equal the contrast travel time for optimal vessel enhancement. In the future, contrast-enhanced MRA may be a potential alternative to angiocardiography in infants and children.

The optimization of scan timing for contrast-enhanced magnetic resonance angiography.

ObjectiveTo determine the optimal scan timing for contrast-enhanced magnetic resonance angiography and to evaluate a new timing method based on the arteriovenous circulation time.Materials and MethodsEighty-nine contrast-enhanced magnetic resonance angiographic examinations were performed mainly in the extremities. A 1.5T scanner with a 3-D turbo-FLASH sequence was used, and during each study, two consecutive arterial phases and one venous phase were acquired. Scan delay time was calculated from the time-intensity curve by the traditional (n = 48) and/or the new (n = 41) method. This latter was based on arteriovenous circulation time rather than peak arterial enhancement time, as used in the traditional method. The numbers of first-phase images showing a properly enhanced arterial phase were compared between the two methods.ResultsMean scan delay time was 5.4 sec longer with the new method than with the traditional. Properly enhanced first-phase images were found in 65% of cases (31/48) using the traditional timing method, and 95% (39/41) using the new method. When cases in which there was mismatch between the target vessel and the time-intensity curve acquisition site are excluded, erroneous acquisition occurred in seven cases with the traditional method, but in none with the new method.ConclusionThe calculation of scan delay time on the basis of arteriovenous circulation time provides better timing for arterial phase acquisition than the traditional method.

3D gadolinium-enhanced MRA: evaluation of hepatic vasculature in children with hepatoblastoma.

We used contrast-enhanced three-dimensional magnetic resonance angiography (3D MRA) modified for pediatric use to evaluate the hepatic vasculature prior to partial hepatectomy in five consecutive children with hepatoblastoma. Modifications included non-breath-hold technique in four of the five children who were sedated. The single breath-hold technique was performed in only one awake child. Scan delay times were based on contrast infusion time rather than total infusion time. The hepatic artery, portal vein, and inferior vena cava were identified in all patients. MRA findings were confirmed by conventional angiography in one patient and by surgery in all. Contrast-enhanced 3D MRA is a useful and rapid technique prior to partial hepatectomy in patients with hepatoblastoma.

Value of a Bolus-Tagging Method on Contrast-Enhanced Abdominal MR Angiography

Purpose : To assess the value of the bolus-tagging method for improving the image quality of contrast-enhanced MR abdominal angiography, and to evaluate the relationship between peak arterial enhancement time and patients’ age, weight and heart rate. Materials and Methods : Contrast-enhanced 3D FISP abdominal MR angiography was performed in 81 patients during a four-month period. The bolus-tagging method was used in a study group comprising 33 patients, and to this end, 1 ml of Gd-DTPA (gadolinium-diethylenetriamine penta-acetic acid) was administered. thirty sequential images (1 image/sec) were then obtained using turbo-FLASH sequencing. After determining peak arterial enhancement time from the time-to-signal intensity curve, optimal scan delay time can be calculated according to the formula used in our patient series. The 48 patients in whom the bolus-tagging method was not used comprised the control group ; in the study group scanning commenced at the optimal scan delay time (and at 10 seconds in the control group) after the administration of 0.2 mM/kg Gd-DTPA using an automatic power injector. Using a three-point scale we evaluated and compared between the two groups the success with which arterial images were obtained. In addition, vascular visibility -an indication of the quality of arteries and veins-was determined using a four-point scale. In the study group, the relationship between peak arterial enhancement time and patients’ age, weight heart rate was also assessed. Results : Pure arterial images were successfully obtained in 32 patients (97%) in the study group and in 40 (83%) in the control group. This difference was not statistically significant (p>.05). With regard to vascular visibility, diagnostic arterial images were seen in 30 patients (91%) in the study group and in 33 patients (69%) in the control group; arterial visibility was significantly better in the study group (p=.0197). On the other hand, the diagnostic venous images were seen in 31 patients (94%) in the study group and in 36 (75%) in the control group; there was no significant difference between the two groups (p=.2367). Peak arterial enhancement time increased significantly with age (r=.443, p=.0098); no correlation,however was seen between peak arterial enhancement time and weight (p>.05) or heart rate (p>.05). Conclusion : Used with contrast-enhanced 3-D FISP MR abdominal angiography, the bolus-tagging method provides better arterial visibility. Peak arterial enhancement time increased significantly with age.

Determination of scan delay time in spiral CT-angiography: utility of a test bolus injection.

The usefulness of a test bolus of contrast medium for predicting the optimal scan delay time in spiral CT-angiography (CTA) was determined. Two axial single level CT studies were performed at the level of the pancreas in 20 patients, first after injection of a 12 ml "test" bolus, second after administration of a 90 ml bolus. The time interval between the start of the test bolus injection and peak aortic enhancement (T-peak) was measured and compared with the time required to reach a 50, 100, and 150 HU level of aortic enhancement after 90 ml bolus injection. The time required to reach 50, 100, and 150 HU enhancement during the 90 ml bolus was largely variable (mean SD 4.9 s). The T-peak varied between 11 and 32 s (mean 20, SD 6.1 s). There was a strong correlation between the T-peak and the time to the different levels of enhancement during the 90 ml bolus (R2 > or = 0.83). The mean time to 50, 100, and 150 HU enhancement was T-peak -3.3 s (SD 2.5 s), T-peak -1.2 s (SD 2.4 s), and T-peak + 1.3 s (SD 2.4 s). The injection of a test bolus improves the timing of a spiral CTA acquisition.

Square-wave voltammetric behaviour and automated determination of cephalothin by a novel sample handling approach.

The voltammetric behaviour of the cephalosporin cephalothin has been studied by rapid-scan square-wave voltammetry at single mercury drops and at the static mercury drop electrode (SMDE). A study of the variation of the peak current with solution variables such as pH, supporting electrolyte, concentration of cephalothin and instrumental variables such as scan speed, pulse width, pulse height and delay time has resulted in optimisation of the reduction signal for analytical purposes. This reduction signal can be used to monitor the degradation of cephalothin in acidic and basic media, and has also been applied to the rapid, accurate and precise determination of cephalothin in a pharmaceutical preparation using an automated sampling handling approach controlled by a polarographic analyser. Concentrations of cephalothin in the range 10–7–10–8M can be determined using this automated approach and involving rapid-scan square-wave voltammetric determination after adsorptive accumulation of cephalothin at the SMDE. The applicability of this latter technique to the determination of cephalothin in body fluids is assessed.