Virtual nonenhanced abdominal dual-energy MDCT: Analysis of image characteristics

AIM:To evaluate abdominal and pelvic image characteristics and artifacts on virtual nonenhanced(VNE) images generated from contrast-enhanced dual-energy multidetector computed tomography(MDCT)studies.METHODS:Hadassah-Hebrew University Medical Institutional Review Board approval was obtained;22 patients underwent clinically-indicated abdominal and pelvic single-source dual-energy MDCT(Philips Healthcare,Cleveland,OH,USA),pre-and post-IV administration of Omnipaque 300 contrast(100 cc).Various solid and vascular structures were evaluated.VNE images were generated from the portal contrast-enhanced phase using probabilistic separation.Contrast-enhanced-,regular nonenhanced(RNE)-,and VNE images were evaluated with a total of 1494 density measurements.The ratio of iodine contrast deletion was calculated.Visualization of calcifications,urinary tract stones,and image artifacts in VNE images were assessed.RESULTS:VNE images were successfully generated in all patients.Significant portal-phase iodine contrast deletion was seen in the kidney(61.7%),adrenal gland(55.3%),iliac artery(55.0%),aorta(51.6%),and spleen(34.5%).Contrast deletion was also significant in the right atrium(RA)(51.5%)and portal vein(39.3%),but insignificant in the iliac vein and inferior vena cava(IVC).Average post contrast-to-VNE HU differences were significant(P<0.05)in the:RA-135.3(SD 121.8),aorta-114.1(SD 48.5),iliac artery-104.6(SD 53.7),kidney-30.3(SD 34.9),spleen-9.2(SD 8.8),and portal vein-7.7(SD 13.2).Average VNE-toRNE HU differences were significant in all organs but the prostate and subcutaneous fat:aorta 38.0(SD 9.3),RA 37.8(SD 16.1),portal vein 21.8(SD 12.0),IVC 12.2(SD 11.6),muscle 3.3(SD 4.9),liver 5.7(SD 6.4),spleen 22.3(SD 9.8),kidney 40.5(SD 6.8),and adrenal 20.7(SD 13.5).On VNE images,196/213 calcifications(92%)and 5/6 renal stones(84%)were visualized.Lytic-like artifacts in the vertebral bodies were seen in all studies.CONCLUSION:Iodine deletion in VNE images is most significant in arteries,and less significant in solid organs and veins.Most vascular and intra-abdominal organ calcifications are preserved.     

Visualisation of intracerebral haemorrhage with flat-detector CT compared to multislice CT: results in 44 cases

The aim of the study was to test the reliability of intracerebral haemorrhage (ICH) detection with C-arm-mounted flat-detector computed tomography (FD-CT) in the angio suite as compared to multislice CT (MSCT). In this study 44 patients with 45 ICH were included. All patients were investigated with MSCT and FD-CT during angiographic evaluation. As a control group we included 16 patients without ICH. In each haematoma we assessed volumetric data of the ICH and counted the numbers of ICH-positive slices. Using interobserver ratings, we additionally investigated the potential of FD-CT to serve as a diagnostic tool to detect ICH. In FD-CT three haematomas were not detected because of motion and beam-hardening artefacts in the region close to the skull base. The r value for the degree of interobserver agreement for the number of slices was 0.95 for MSCT and 0.94 for FD-CT. Measurements of the area and the calculated volume of the ICH showed high inter- and intraobserver agreement. Our results indicate that FD-CT is a helpful tool in the daily emergency management of ICH patients as detection of ICH was found to be nearly as reliable as in MSCT. Limitations of this technology are motion and beam-hardening artefacts that may mask small haematomas located in the posterior fossa or the skull base.     

Computed tomography of the bowel: A prospective comparison study between four techniques

Objectives

The major objective was to prospectively compare the grade of bowel distension obtained with four different computed tomography (CT) techniques dedicated for the examination of the small intestine (CT enteroclysis [CTE] and enterography [CTe]), of the colon (CT with water enema [CT-WE]), or both (CTe with water enema [CTe-WE]). The secondary objective was to assess patients’ tolerance toward each CT protocol.

Materials and methods

Recruitment was designed to obtain four groups of the same number of patients (30). Each group corresponded to a specific CT technique, for a total of 120 consecutive outpatients (65 male and 55 female, mean age 51.09 ± 13.36 years).CTE was performed after injection of methylcellulose through a nasojejunal tube, while in the CTe protocol a polyethylene glycol electrolyte solution was orally administered to patients prior to the CT acquisition. In the CT-WE protocol intraluminal contrast (water) was administered only by a rectal enema, while CTe-WE technique included both a rectal water enema and oral ingestion of neutral contrast material to obtain a simultaneous distension of small and large bowel.CT studies were reviewed in consensus by two gastrointestinal radiologists who performed a quantitative and qualitative analysis of bowel distension on a per segment basis. The presence and type of adverse effects were recorded.

Results

CTE provided the best distension of jejunal loops (median diameter 27 mm, range 17–32 mm) when compared to all the other techniques (p < 0.0001). The frequency of patients with an adequate distension of the terminal ileum was not significantly different among the four groups (p = 0.0608). At both quantitative and qualitative analysis CT-WE and CTe-WE determined a greater and more consistent luminal filling of the large intestine than that provided by both CTE and CTe (p < 0.0001 for all colonic segments). Adverse effects were more frequent in patients belonging to the CTE group (p < 0.0028).

Conclusions

CTE allows an optimal distension of jejunal loops, but it is the most uncomfortable CT protocol. When performing CT-WE, an adequate retrograde distension of the terminal ileum was provided in a particularly high percentage of patients. CTe-WE provides a simultaneous optimal distension of both small and large bowel.     

Gated blood-pool emission tomography: A new technique for the investigation of cardiac structure and function

ECG-gated single-photon emission-computed tomography of the intracardiac blood pool is a new technique that has not previously been widely applied. It involves the acqusition of ECG-gated images of the intracardiac blood pools labelled with sodium pertechnetate Tc 99m in 32 projections around the left-anterior hemithorax using a rotating gamma camera. From these images, tomographic sections are reconstructed orthogonal to the long axis of the left ventricle. The heart is therefore imaged three dimensionally, and more extensive information is obtained than in planar radionuclide ventriculography where imaging is usually restricted to only a single projection. Both structure and function can be studied, and the left-ventricular volume and ejection fraction, and wall motion are obtained. Of 50 patients studied, 7 cases are illustrated in order to show normal findings, examples of wall motion that were not shown by planar-contrast and radionuclide ventriculography, examples of the localisation of ventricular hypertrophy, and a comparison between blood-pool and ²⁰¹TI myocardial tomography.This work was supported by the Sir Jules Thorn Charitable Trust     

PET-CT在乳腺癌诊断中的应用价值

乳腺癌是当今大多数国家妇女最常见的恶性肿瘤.在过去的数十年中,正电子发射体层显像（PET）的应用极大地提高了乳腺肿瘤的临床诊治率.然而由于PET对肿瘤病灶缺乏准确的解剖定位而使18F-氟代脱氧葡萄糖（18F-FDG）PET临床应用的准确性受到限制.PET-CT的完美结合使对肿瘤的解剖定位和诊断的敏感性及特异性得到了明显的提高.本文着重介绍PET-CT在乳腺癌治疗后再分期、疗效观察、术前分期和放疗计划拟定中的应用价值.     

PET-CT在乳腺癌诊断中的应用价值

乳腺癌是当今大多数国家妇女最常见的恶性肿瘤。在过去的数十年中,正电子发射体层显像(PET)的应用极大地提高了乳腺肿瘤的临床诊治率。然而由于PET对肿瘤病灶缺乏准确的解剖定位而使18F-氟代脱氧葡萄糖(18F-FDG) PET临床应用的准确性受到限制。PET-CT的完美结合使对肿瘤的解剖定位和诊断的敏感性及特异性得到了明显的提高。本文着重介绍PET-CT在乳腺癌治疗后再分期、疗效观察、术前分期和放疗计划拟定中的应用价值。     

Spectral photon-counting CT in cardiovascular imaging

Photon-counting computed tomography (PCCT) is an emerging technology promising to substantially improve cardiovascular imaging. Recent engineering and manufacturing advances by several vendors are expected to imminently launch this new technology into clinical reality. Photon-counting detectors (PCDs) have multiple potential advantages over conventional energy integrating detectors (EIDs) such as the absence of electronic noise, multi-energy capability, and increased spatial resolution. These developments will have different timescales for implementation and will affect different clinical scopes. We describe the technical aspects of PCCT, explain the current developments, and finally discuss potential advantages of PCCT in cardiovascular imaging.     

PET/CT——功能与解剖结构的同机图像融合

PET/CT为近几年出现的一种新技术,将PET与CT安装在同一机架上,一次扫描可获得PET与CT的融合图像,对定位诊断肿瘤、指导肿瘤放疗计划、选择活检部位及监测疗效等具有重要价值,同时,CT提供了一种PET衰减校正的方法。本文简要介绍PET/CT的结构设计与性能、优势及目前尚存在的技术问题。     

Performance of the new generation of whole-body PET/CT scanners: Discovery STE and Discovery VCT

Purpose The new GE Discovery STE and Discovery VCT respectively combine 16-slice and 64-slice CT with PET. The PET scanner has a new BGO detector block of 8×6 matrix (6.3×4.7×30 mm³). The aim of this study was to test the performance of the new scanner. Methods The PET performance evaluation was done using NEMA methodology. Owing to improved front-end electronics, the system was tested with different energy window and coincidence timing settings. Results Transaxial resolution FWHM for 2D(3D) mode at 1 cm offset from the centre of the field of view (R1) was 4.87 mm (5.12 mm) and at 10 cm off centre (R10) radially 5.70 mm (5.89 mm) and tangentially 5.84 mm (5.47 mm). The axial resolutions were 4.4 mm (5.18 mm) (R1) and 5.99 mm (5.86 mm) (R10). The sensitivities were 2.3 cps/kBq (8.8 cps/kBq) (R0, centre of field of view) and 2.3 cps/kBq (8.9 cps/kBq) (R10). The system scatter fraction was 21.4% in 2D at an energy of 375 keV (33.9% in 3D mode at a higher energy of 425 keV). Peak noise equivalent count rates (k=1) were 84.9 kcps at 43.9 kBq/ml (2D) and 67.6 kcps at 12.1 kBq/ml (3D). In image quality measurement the hot sphere to background contrast with 10- to 22-mm diameter spheres varied from 14% to 68%, being slightly better in 3D than in 2D mode. Cold sphere contrast was 67% in 2D and 59% in 3D mode. Conclusion GE’s new STE and VCT PET/CT systems have improved spatial resolution without loss in sensitivity. When compared with the LYSO crystal-based GE Discovery RX, the resolution and scatter fraction are comparable, the count rate capability is lower but the sensitivity is higher.     

^18F-FDG PET-CT结合HRCT诊断细支气管肺泡癌的价值

目的探讨^18F-FDG PET-CT结合HRCT诊断细支气管肺泡癌的价值。方法回顾分析经病理证实的24例细支气管肺泡癌患者的PET-CT及其HRCT图像资料。分别记录其形态学表现及放射性分布，同时测量其最大SUV值（SUVmax）。结果根据形态学表现分为3型：（1）孤立结节型（12例）：表现为密度略不均匀或并有磨玻璃样密度的单发结节，主要征象为分叶、短毛刺、支气管充气征、胸膜凹陷征、空泡征、晕征、血管集束征。SUVmax均值为3．78±1．54；（2）多发结节型（5例）：表现为两肺散在多发的结节，以中下肺叶为主，结节大小不一，小结节无放射性聚积，对于直径〉5mm的结节，SUVmax均值为3．46±1．32。（3）肺炎型（7例）：为一个或多个肺叶的实变。其内见充气支气管征或蜂窝征，放射性分布不均匀，部分病灶FDG摄取为阴性。结论^18F-FDG PET-CT结合HRCT在细支气管肺泡癌的诊断中具有重要的应用价值。诊断时要密切结合PET与HRCT图像，以最大限度地减少误诊。     

Late-arterial and portal-venous phase imaging of the liver with a multislice CT scanner in patients without circulatory disturbances: automatic bolus tracking or empirical scan delay?

The value of automatic bolus tracking in late-arterial and portal-venous phase imaging of the liver with a multislice CT scanner as compared with fixed time-delay examination in patients without circulatory disturbances is evaluated. For the evaluation of known or suspected liver disease, 98 multiphase contrast-enhanced CT examinations including double late-arterial phase imaging were randomized into either scanning with a scan delay of 30 s from the beginning of contrast material injection or scanning with automatic bolus tracking. Contrast material was injected at 0.07 ml/kg body weight/s over 30 s. Contrast enhancement in each acquisition was measured in the aorta, portal vein, liver, pancreas and hepatocellular carcinomas. The density difference between hepatocellular carcinomas and the hepatic parenchyma was calculated. The mean time to the first-pass acquisition as determined by automatic bolus tracking was 29.6 s. No statistically significant difference was observed between the two groups either in any enhancement in any acquisition or in the lesion-to-liver density difference. The use of automatic bolus tracking in late-arterial and portal-venous phase hepatic CT does not significantly improve the degree of contrast enhancement in the aorta, portal vein, liver and pancreas or lesion-to-liver conspicuity in patients without circulatory disturbances.     

Multislice computed tomography perfusion imaging for visualization of acute pulmonary embolism: animal experience

The purpose of our animal study was to evaluate a new computed tomography (CT) subtraction technique for visualization of perfusion defects within the lung parenchyma in subsegmental pulmonary embolism (PE). Seven healthy pigs were entered into a prospective trial. Acute PE was artificially induced by fresh clot material prior to the CT scans. Within a single breath-hold, whole thorax CT scans were performed with a 16-slice multidetector-row CT scanner (SOMATOM Sensation 16; Siemens, Forchheim, Germany) before and after intravenous application of 80 ml of contrast medium with a flow rate of 4 ml/s, followed by a saline chaser. The scan parameters were 120 kV and 100 mAs_eff, using a thin collimation of 16×0.75 mm and a table speed/rotation of 15–18 mm (pitch, 1.25–1.5; rotation time, 0.5 s). Axial source images were reconstructed with an effective slice thickness of 1 mm (overlap, 30%). A new automatic subtraction technique was used. After 3D segmentation of the lungs in the plain and contrast-enhanced series, threshold-based extraction of major airways and vascular structures in the contrast images was performed. This segmentation was repeated in the plain CT images segmenting the same number of vessels and airways as in the contrast images. Both scans were registered onto each other using nonrigid registration. After registration both image sets were filtered in a nonlinear fashion excluding segmented airways and vessels. After subtracting the plain CT data from the contrast data the resulting enhancement images were color-encoded and overlaid onto the contrast-enhanced CT angiography (CTA) images. This color-encoded combined display of parenchymal enhancement of the lungs was evaluated interactively on a workstation (Leonardo, Siemens) in axial, coronal and sagittal plane orientations. Axial contrast-enhanced CTA images were rated first, followed by an analysis of the combination images. Finally, CTA images were reread focusing on areas with perfusion deficits indicating PE on the color-coded enhancement display. Subtraction was feasible for all seven studies. In one animal, opacification of the pulmonary arteries was suboptimal owing to heart insufficiency. In the remaining six pigs, a total of 37 perfusion defects were clearly assessable downstream of occluded subsegmental arteries, showing lower or missing enhancement compared with normally perfused lung parenchyma. Indeterminate findings from CTA showed typical PE perfusion defects in four out of six cases on CT subtraction. Additionally, 22 peripheral triangular-shaped enhancement defects were delineated. Nine of these findings were reclassified as definitely being caused by PE on second reading of the CTA data sets. Our initial results have shown that this new subtraction technique for perfusion imaging of PE is feasible, using routine contrast delivery. Dedicated examination protocols are mandatory for adequate opacification of the pulmonary arteries and for optimization of data sets for subsequent subtraction. Perfusion imaging allows a comprehensive assessment of morphology and function, providing more accurate information on acute PE.This paper contains data on behalf of the Amersham Health Research Fellowship Grant, ECR 2003.     

Gamma camera-mounted anatomical X-ray tomography: technology, system characteristics and first images

Scintigraphic diagnosis, based on functional image interpretation, becomes more accurate and meaningful when supported by corresponding anatomical data. In order to produce anatomical images that are inherently registered with images of emission computerised tomography acquired with a gamma camera, an X-ray transmission system was mounted on the slip-ring gantry of a GEMS Millennium VG gamma camera. The X-ray imaging system is composed of an X-ray tube and a set of detectors located on opposite sides of the gantry rotor that moves around the patient along with the nuclear detectors. A cross-sectional anatomical transmission map is acquired as the system rotates around the patient in a manner similar to a third-generation computerised tomography (CT) system. Following transmission, single-photon emission tomography (SPET) or positron emission tomography (PET) coincidence detection images are acquired and the resultant emission images are thus inherently registered to the anatomical maps. Attenuation correction of the emission images is performed with the same anatomical maps to generate transmission maps. Phantom experiments of system performance and examples of first SPET and coincidence detection patient images are presented. Despite limitations of the system when compared with a state of the art CT scanner, the transmission anatomical maps allow for precise anatomical localisation and for attenuation correction of the emission images. Received 27 October 1999 and in revised form 10 February 2000     

Evaluation of computed tomography coronary angiography in patients with a high heart rate using 16-slice spiral computed tomography with 0.37-s gantry rotation time

The aim of our study is to evaluate computed tomography (CT) coronary angiography in patients with a high heart rate using 16-slice spiral CT with 0.37-s gantry rotation time. We compare the image quality of patients whose heart rates were over 70 beats per minute (bpm) with that of patients whose heart rates were 70 bpm or less. Sixty patients with various heart rates underwent retrospectively ECG-gated multislice spiral CT (MSCT) coronary angiography. Two experienced observers who were blind to the heart rates of the patients evaluated all the MSCT coronary angiographic images and calculated the assessable segments. A total of 620 out of 891 (69.6%) segments were satisfactorily visualized. On average, 10.3 coronary artery segments per patient could be evaluated. In 36 patients whose heart rates were below 70 bpm [mean 62.2 bpm±5.32 (standard deviation, SD)], the number of assessable segments was 10.72±2.02 (SD). In the other 24 patients whose heart rates were above 70 bpm [mean 78.6 bpm±8.24 (SD)], the corresponding number was 9.75±1.74 (SD). No statistically significant difference was found in these two subgroups t test, P>0.05. The new generation of 16-slice spiral CT with 0.37-s rotation time can satisfactorily evaluate the coronary arteries of patients with high heart rates (above 70 bpm, up to 102 bpm).     

Evaluation of recurrent gastric malignancy with [F-18]-FDG positron emission tomography

AIM: We retrospectively assessed the use of [(18)F] fluorodeoxyglucose positron emission tomography (FDG PET) in the evaluation of recurrent disease in patients with history of gastric malignancy. MATERIALS AND METHODS: Eighteen patients were referred for FDG PET for evaluation of recurrent gastric cancer. Prior treatments included total (n = 4) or partial gastrectomy (n = 14) followed by chemotherapy alone (n = 7) or combined chemoradiation therapy (n = 2). The interval between the most recent treatment and PET ranged from 3 months to 2 years. Correlative diagnostic data were available in 16 patients and were all obtained within 3 months of the PET study. Validation was by clinical or imaging follow-up (2-45 months) in 16 patients and histology in two patients. RESULTS: PET was concordant with computed tomography (CT) in 12 patients (5 TP, 6 TN, 1 FN). In one patient with negative imaging studies, an incidental finding of left obstructive uropathy was determined to be due to metastatic ureteral stricture. Discordant imaging findings were present in four patients (22% of total). PET-detected diffuse metastatic lesions in three of these patients with rising serum tumour markers while other imaging studies were negative. Additional chemotherapy was initiated in these three patients (17% of total) based on PET localization of disease. PET and a gastric anastomosis biopsy were negative in another patient with positive CT. The remaining two patients without correlative imaging studies died shortly after positive PET studies with presumed recurrent cancer. CONCLUSION: FDG PET may be useful in the evaluation of recurrent gastric cancer, and can localize the disease when CT is non-diagnostic. Imaging evaluation with PET may also impact on the clinical management of patients with recurrent gastric cancer.     

Role of cardiac computed tomography in patients with suspected coronary artery disease: interaction with nuclear cardiology

Coronary computed tomography (CT) angiography (CTA) and myocardial perfusion single photon emission CT (SPECT, or MPS) provide complementary information on vascular structure and myocardial perfusion. In patients with coronary artery disease (CAD), the combination of both methods is helpful for disease detection and therapeutic strategy planning. This article addresses the utility of coronary CTA with current 64-row multidetector CT instruments, MPS, and the combination of these methods in the evaluation of CAD.     

Detection of simulated vertical root fractures; which is better multi-detector computed tomography or cone beam computed tomography?

Objectives

Multi-detector computed tomography (MDCT) and cone beam computed tomography (CBCT) were compared regarding their ability to detect vertical root fractures.

Value of contrast enhanced CT scanning in the non-trauma emergency room patient

Summary To determine the value of performing contrast CT in addition to non-contrast CT in the evaluation of acute non-traumatic central nervous system disorders, we retrospectively reviewed 322 cases originating from the emergency room at our institution. The most common indication for scanning was seizure activity (34% of total), followed by headache (30%), focal neurological deficit (10%), and altered mental status (8%). 75% of the noncontrast scans were normal. The contrast-enhanced scan revealed abnormalities not evident on the non-contrast scan in only three of these cases, and the information did not alter patient management. We concluded that in the acute setting, if a non-contrast CT is normal, a contrast study is usually unnecessary. Therefore, given the additional risks of contrast infusion, the contrast study, if needed, is generally best obtained at a later date, after more careful evaluation of the patient's history and medical records. If the non-contrast CT scan is abnormal, a contrast enhanced CT scan may be beneficial, but, again, is often not needed to direct acute patient management.