图像域迭代重建算法对腹部CT平扫图像质量和辐射剂量的影响

目的:探讨图像域迭代重建算法对腹部CT平扫图像质量及辐射剂量的影响。 方法:以辽阳市中心医院2017年1月~2018年4月行腹部CT平扫的150例患者为研究对象,依据就诊先后顺序随机将其分为观察组与对照组,各75例。均行自动毫安控制技术扫描,管电压均为130 kV。观察组预设图像质量参考毫安秒150 mAs,行图像域迭代重建算法重建;对照组预设图像质量参考毫安秒250 mAs,行滤波反投影重组。通过CT值、图像噪声SD、图像信噪比、对比噪声比评价两组图像客观质量,并行图像质量主观评价,记录两组CT剂量容积指数。 结果:观察组肝脏、脾脏的图像噪声SD均显著低于对照组,图像信噪比均显著高于对照组,差异有统计学意义（P<0.05）;CT值、对比噪声比、主观整体质量评分两组比较差异均无统计学意义（P>0.05）;观察组CT剂量容积指数为（10.02±2.85） mGy,显著低于对照组的（15.68±4.36） mGy,差异有统计学意义（P<0.05）。 结论:图像域迭代重建算法不仅能保证腹部CT平扫图像质量,而且能有效减少辐射剂量。     

Dual time point imaging of FDG PET/CT in a tuberculous spondylodiscitis

Dual Time Point Imaging (DTPI) technique is a specialised protocol adopted in (18)F-Fluorodeoxyglucose (FDG) Positron Emission Tomography (PET) imaging. This technique is claimed to be useful in differentiating malignant and infective lesions. The authors adopted this technique in a patient diagnosed with tuberculous spondylodiscitis and psoas abscess which demonstrated higher Maximum Standardized Uptake Value (SUVmax) during initial scans as compared with those obtained on delayed scans. The SUVmax changes between the two time points are believed to be a valuable finding for chronic granulomatous infective lesions such as tuberculosis.     

Respiratory-gated CT as a tool for the simulation of breathing artifacts in PET and PET/CT

Respiratory motion in PET and PET/CT blurs the images and can cause attenuation-related errors in quantitative parameters such as standard uptake values. In rare instances, this problem even causes localization errors and the disappearance of tumors that should be detectable. Attenuation errors are severe near the diaphragm and can be enhanced when the attenuation correction is based on a CT series acquired during a breath-hold. To quantify the errors and identify the parameters associated with them, the authors performed a simulated PET scan based on respiratory-gated CT studies of five lung cancer patients. Diaphragmatic motion ranged from 8 to 25 mm in the five patients. The CT series were converted to 511-keV attenuation maps which were forward-projected and exponentiated to form sinograms of PET attenuation factors at each phase of respiration. The CT images were also segmented to form a PET object, moving with the same motion as the CT series. In the moving PET object, spherical 20 mm mobile tumors were created in the vicinity of the dome of the liver and immobile 20 mm tumors in the midchest region. The moving PET objects were forward-projected and attenuated, then reconstructed in several ways: phase-matched PET and CT, gated PET with ungated CT, ungated PET with gated CT, and conventional PET. Spatial resolution and statistical noise were not modeled. In each case, tumor uptake recovery factor was defined by comparing the maximum reconstructed pixel value with the known correct value. Mobile 10 and 30 mm tumors were also simulated in the case of a patient with 11 mm of breathing motion. Phase-matched gated PET and CT gave essentially perfect PET reconstructions in the simulation. Gated PET with ungated CT gave tumors of the correct shape, but recovery was too large by an amount that depended on the extent of the motion, as much as 90% for mobile tumors and 60% for immobile tumors. Gated CT with ungated PET resulted in blurred tumors and caused recovery errors between -50% and +75%. Recovery in clinical scans would be 0%-20% lower than stated because spatial resolution was not included in the simulation. Mobile tumors near the dome of the liver were subject to the largest errors in either case. Conventional PET for 20 mm tumors was quantitative in cases of motion less than 15 mm because of canceling errors in blurring and attenuation, but the recovery factors were too low by as much as 30% in cases of motion greater than 15 mm. The 10 mm tumors were blurred by motion to a greater extent, causing a greater SUV underestimation than in the case of 20 mm tumors, and the 30 mm tumors were blurred less. Quantitative PET imaging near the diaphragm requires proper matching of attenuation information to the emission information. The problem of missed tumors near the diaphragm can be reduced by acquiring attenuation-correction information near end expiration. A simple PET/CT protocol requiring no gating equipment also addresses this problem.     

PET/CT image registration: preliminary tests for its application to clinical dosimetry in radiotherapy

The quality of dosimetry in radiotherapy treatment requires the accurate delimitation of the gross tumor volume. This can be achieved by complementing the anatomical detail provided by CT images through fusion with other imaging modalities that provide additional metabolic and physiological information. Therefore, use of multiple imaging modalities for radiotherapy treatment planning requires an accurate image registration method. This work describes tests carried out on a Discovery LS positron emission/computed tomography (PET/CT) system by General Electric Medical Systems (GEMS), for its later use to obtain images to delimit the target in radiotherapy treatment. Several phantoms have been used to verify image correlation, in combination with fiducial markers, which were used as a system of external landmarks. We analyzed the geometrical accuracy of two different fusion methods with the images obtained with these phantoms. We first studied the fusion method used by the PET/CT system by GEMS (hardware fusion) on the basis that there is satisfactory coincidence between the reconstruction centers in CT and PET systems; and secondly the fiducial fusion, a registration method, by means of least-squares fitting algorithm of a landmark points system. The study concluded with the verification of the centroid position of some phantom components in both imaging modalities. Centroids were estimated through a calculation similar to center-of-mass, weighted by the value of the CT number and the uptake intensity in PET. The mean deviations found for the hardware fusion method were: deltax/ +/-sigma = 3.3 mm +/- 1.0 mm and /deltax/ +/-sigma = 3.6 mm +/- 1.0 mm. These values were substantially improved upon applying fiducial fusion based on external landmark points: /deltax/ +/-sigma = 0.7 mm +/- 0.8 mm and /deltax/ +/-sigma = 0.3 mm 1.7 mm. We also noted that differences found for each of the fusion methods were similar for both the axial and helical CT image acquisition protocols.     

Minimizing artifacts resulting from respiratory and cardiac motion by optimization of the transmission scan in cardiac PET/CT

The introduction of positron emission/computed tomography (PET/CT) systems coupled with multidetector CT arrays has greatly increased the amount of clinical information in myocardial perfusion studies. The CT acquisition serves the dual role of providing high spatial anatomical detail and attenuation correction for PET. However, the differences between the interaction of respiratory and cardiac cycles in the CT and PET acquisitions presents a challenge when using the CT to determine PET attenuation correction. Three CT attenuation correction protocols were tested for their ability to produce accurate emission images: gated, a step mode acquisition covering the diastolic heart phase; normal, a high-pitch helical CT; and slow, a low-pitch, low-temporal-resolution helical CT. The amount of cardiac tissue in the emission image that overlaid lung tissue in the transmission image was used as the measure of mismatch between acquisitions. Phantom studies simulating misalignment of the heart between the transmission and emission sequences were used to correlate the amount of mismatch with the artificial defect changes in the emission image. Consecutive patients were studied prospectively with either paired gated (diastolic phase, 120 kVp, 280 mA, 2.6 s) and slow CT (0.562:1 pitch, 120 kVp, Auto-mA, 16 s) or paired normal (0.938:1 pitch, 120 kVp, Auto-mA, 4.8 s) and slow CT protocols, prior to a Rb-82 perfusion study. To determine the amount of mismatch, the transmission and emission images were converted to binary representations of attenuating tissue and cardiac tissue and overlaid using their native registration. The number of cardiac tissue pixels from the emission image present in the CT lung field yielded the magnitude of misalignment represented in terms of volume, of where a small volume indicates better registration. Acquiring a slow CT improved registration between the transmission and emission acquisitions compared to the gated and normal CT protocols. The volume of PET cardiac tissue in the CT lung field was significantly lower (p < 0.03) for the slow CT protocol in both the rest and stress emission studies. Phantom studies showed that an overlaying volume greater than 2.6 mL would produce significant artificial defects as determined by a quantitative software package that employs a normal database. The percentage of patient studies with overlaying volume greater than 2.6 mL was reduced from 71% with the normal CT protocol to 28% with the slow CT protocol. The remaining 28% exhibited artifacts consistent with heart drift and patient motion that could not be corrected by adjusting the CT acquisition protocol. The low pitch of the slow CT protocol provided the best match to the emission study and is recommended for attenuation correction in cardiac PET/CT studies. Further reduction in artifacts arising from cardiac drift is required and warrants an image registration solution.     

Single and dual energy attenuation correction in PET/CT in the presence of iodine based contrast agents

In present positron emission tomography (PET)/computed tomography (CT) scanners, PET attenuation correction is performed by relying on the information given by a single CT scan. The scaling of the linear attenuation coefficients from CT x-ray energy to PET 511 keV gamma energy is prone to errors especially in the presence of CT contrast agents. Attenuation correction based upon two CT scans at different energies but performed at the same time and patient position should reduce such errors and therefore improve the accuracy of the reconstructed PET images at the cost of introduced additional noise. Such CT scans could be provided by future PET/CT scanners that have either dual source CT or energy sensitive CT. Three different dual energy scaling methods for attenuation correction are introduced and assessed by measurements with a modified NEMA 1994 phantom with different CT contrast agent concentrations. The scaling is achieved by differentiating between (1) Compton and photoelectric effect, (2) atomic number and density, or (3) water-bone and water-iodine scaling schemes. The scaling method (3) is called hybrid dual energy computed tomography attenuation correction (hybrid DECTAC). All three dual energy scaling methods lead to a reduction of contrast agent artifacts with respect to single energy scaling. The hybrid DECTAC method resulted in PET images with the weakest artifacts. Both, the hybrid DECTAC and Compton/photoelectric effect scaling resulted also in images with the lowest PET background variability. Atomic number/density scaling and Compton/photoelectric effect scaling had problems to correctly scale water, hybrid DECTAC scaling and single energy scaling to correctly scale Teflon. Atomic number/density scaling and hybrid DECTAC could be generalized to reduce these problems.     

Dry small pleural dissemination of adenocarcinoma of the lung preoperatively detected by PET/CT: a report of two cases

Dry pleural dissemination in non-small cell lung cancer, defined as solid pleural metastasis of lung cancer without pleural effusion, is a condition occurring in T4 lung cancer. Positron emission tomography (PET) has been reported to be useful for the diagnosis and staging of lung cancer. It has been reported that positive findings on PET scans of indeterminate pleural abnormalities at computed tomography (CT) are sensitive to malignancy. We encountered two cases of dry small pleural dissemination of adenocarcinoma of the lung preoperatively detected by PET/CT. A 75-year-old man and a 66-year-old man underwent CT scan, which demonstrated solitary tumor in the lung, an enlarged mediastinal lymph node, and a small pleural nodule less than 10 mm in size, all of which were positive findings on the fluorine 18 fluorodeoxyglucose (FDG) PET portion of an integrated PET/CT. Both patients underwent thoracoscopic biopsy of the dry pleural nodule revealing dissemination of adenocarcinoma of the lung (T4). Whereas histological thoracoscopic diagnosis remains mandatory before planning treatment, our cases may suggest that PET/CT will be useful as a screening modality for dry pleural dissemination of lung cancer.     

18 F-FDG PET/CT显像联合血清肿瘤标志物检测在肺单发结节诊断中的价值

目的 探讨18F-FDG PET/CT显像和血清肿瘤标志物(CEA、NSE、CFRA21-1)检测联合在肺单发结节诊断中的价值.方法 91例经病理确诊的肺单发结节患者进行18F-FDG PET/CT显像,同时取静脉血4mL分离取血清在低温冰箱保存,用放免法集中测量血肿瘤标志物CEA、NSE、CFRA21-1.结果 18 F-FDG PET/CT检查对肺单发结节恶性肿瘤检出的灵敏度为84.8%(56/66),对肺单发结节诊断的准确率为86.8%(79/91);18 F-FDG PET/CT显像联合血肿瘤标志物(CEA+NSE+CFRA21-1)检测对肺单发结节恶性肿瘤检出的灵敏度为93.9%(62/66),对肺单发结节诊断的准确率为95.6%(87/91),和18F-FDG PET/CT检查相比,灵敏度和准确率差异具有统计学意义(P均﹤0.05).结论 18 F-FDG PET/CT显像和血肿瘤标志物(CEA、NSE、CFRA21-1)检测联合能提高对肺单发结节诊断的灵敏度和准确性,有较高的临床应用价值.     

Diagnostic value of SPECT, PET and PET/CT in the diagnosis of coronary artery disease: A systematic review

Purpose:

The purpose of the study was to investigate the diagnostic value of SPECT, PET and PET/CT in the diagnosis of coronary artery disease, based on a systematic review.

Material and Methods:

A search of PubMed/Medline and Sciencedirect databases in the English-language literature published over the last 24 years was performed. Only studies with at least 10 patients comparing SPECT, PET or combined PET/CT with invasive coronary angiography in the diagnosis of coronary artery disease (50% stenosis) were included for analysis. Sensitivities and specificities estimates pooled across studies were analysed using a Chi-square test.

Results:

Twenty-five studies met the selection criteria and were included for the analysis. Ten studies were performed with SPECT alone; while another six studies were performed with PET alone. Five studies were carried out with both PET and SPECT modalities, and the remaining four studies were investigated with integrated PET-CT. The mean value of sensitivity, specificity and accuracy of these imaging modalities for the diagnosis of coronary artery disease was 82% (95%CI: 76 to 88), 76% (95%CI: 70 to 82) and 83% (95%CI: 77 to 89) for SPECT; 91% (95%CI: 85 to 97), 89% (95%CI: 83 to 95) and 89% (95%CI: 83 to 95) for PET; and 85% (95%CI: 79 to 90), 83% (95%CI: 77 to 89) and 88% (95%CI: 82 to 94) for PET/CT, respectively. The diagnostic accuracy of these imaging modalities was dependent on the radiotracers used in these studies, with ammonia resulting in the highest diagnostic value.

Conclusion:

Our review shows that PET has high diagnostic value for diagnosing coronary artery disease, and this indicates that it is a valuable technique for both detection and prediction of coronary artery disease.     

Impact of target-to-background ratio, target size, emission scan duration, and activity on physical figures of merit for a 3D LSO-based whole body PET/CT scanner

The aim of our work is to describe the way in which physical figures of merit such as contrast-to-noise ratio (CNR) behave when varying acquisition parameters such as emission scan duration (ESD) or activity at the start of acquisition (A(acq)) that in clinical practice can be selected by the user, or object properties such as target dimensions or target-to-background (T/B) ratio, which depend uniquely on the intrinsic characteristics of the object being imaged. Figures of merit, used to characterize image quality and quantitative accuracy for a 3D-LSO based PET/CT scanner, were studied as a function of ESD and A(acq) for different target sizes and T/B ratios using a multivariate approach in a wide range of conditions approaching the ones that can be encountered in clinical practice. An annular ring of water bags of 3 cm thickness was fitted over an IEC phantom in order to obtain counting rates similar to those found in average patients. The average scatter fraction (SF) of the modified IEC phantom was similar to the mean SF measured on patients with a similar scanner. A supplemental set of micro-hollow spheres was positioned inside the phantom. The NEMA NU 2-2001 scatter phantom was positioned at the end of the IEC phantom to approximate the clinical situation of having activity that extends beyond the scanner. The phantoms were filled with a solution of water and 18F (12 kBq/mL) and the spheres with various T/B ratios of 22.5, 10.3, and 3.6. Sequential imaging was performed to acquire PET images with varying background activity concentrations of about 12, 9, 6.4, 5.3, and 3.1 kBq/mL, positioned on the linear portion of the phantom's NECR curve, well below peak NECR of 61.2 kcps that is reached at 31.8 kBq/mL. The ESD was set to 1, 2, 3, and 4 min/bed. With T/B ratios of 3.6, 10.3, and 22.5, the 13.0, 8.1, and 6.5 mm spheres were detectable for the whole ranges of background activity concentration and ESD, respectively. The ESD resulted as the most significant predictor of CNR variance, followed by T/B ratio and the cross sectional area of the given sphere. Only last comes A(acq) with a weight more than halved with respect to ESD. Thus, raising ESD seems to be much more effective than raising A(acq) in order to obtain higher CNR, which is the physical figure of merit closely related with target detectability, at least in the simple task of the signal known exactly background known exactly model.     

Role of 18F-FDG PET/CT in the Carcinoma of the Uterus: A Review of Literature

In the present review we reported the value of 18F-fluorodeoxyglucose (FDG) PET/CT in face of uterine cancer, in terms of sensitivity, specificity and accuracy. Moreover, we made a comparison with the other imaging techniques currently used to evacuate these tumors including contrast-enhanced CT, contrast enhanced-MRI and transvaginal ultrasonography. FDG PET/CT has been reported to be of particular value in detecting occult metastatic lesions, in prediction of response to treatment and as a pro-gnostic factor.     

Metastatic squamous cell carcinoma of the gingiva appearing as a solitary branchial cyst carcinoma: diagnostic role of PET/CT

We herein present a case of a left cervical cystic mass, for which the initial pathological diagnosis was branchial cleft cyst carcinoma (following complete mass excision). Thorough postoperative examinations, including with FDG positron emission tomography/computed tomography (PET/CT), revealed a primary tumor in the retromolar region of the left mandible. A 52-year-old female presented with a 2-month history of a painless, progressively enlarged left-sided neck mass. Fine-needle aspiration biopsy suggested a branchial cleft cyst. Physical examination revealed a 3 × 3-cm smooth, tender mass in the upper-left neck and anterior border of the sternocleidomastoid muscle. Examination using nasendoscopy and a strobolaryngoscope revealed no abnormalities of the nasal cavity, nasopharynx, oropharynx, hypopharynx or larynx. MRI of the neck revealed a solitary, round, cystic mass under the left parotid gland. The mass was excised completely. Pathologic results indicated a branchial cleft cyst carcinoma. According to the diagnostic criteria for a branchial cleft cystic carcinoma, PET/CT was performed to detect the occult primary site. PET/CT revealed high FDG uptake in the tooth root of the left mandible. Frozen sections of the mass were indicative of moderate, differentiated squamous cell carcinoma. The carcinoma in the retromolar region of the left mandible was locally excised under general anesthesia. A partial left maxillectomy, partial mandibulectomy, and left radical neck dissection were performed. The patient received postoperative concurrent chemoradiotherapy, and was disease-free at the 8-month follow-up. True branchial cleft cyst carcinoma is rare: once diagnosed, it should be distinguished from metastatic cystic cervical lymph and occult primary carcinoma. FDG PET/CT is useful in the identification of occult primary tumor.     

18F-FDG PET/CT与CT诊断胃癌淋巴结转移直接比较的系统评价

目的 采用Meta分析和直接比较方法系统评价18F-FDG PET/CT与CT对胃癌淋巴结转移的诊断价值.方法 使用计算机系统检索中国期刊全文数据库、中文科技期刊数据库、万方数据库、PubMed、Embase、The Cochrane Library,从建库至2016年11月,搜索直接比较18F-FDG PET/CT与CT诊断胃癌淋巴结转移的诊断性比较试验.用Meta-Disc1.4软件进行分析,计算两种影像学诊断方法的合并灵敏度(sensitivity,SEN)、合并特异性(specificity,SPE)、合并阳性似然比(positive likelihood ratio,+LR)、合并阴性似然比(negative likelihood ratio,-LR),诊断优势比(diagnostic OR,DOR),并绘制SROC (summary receiver operating characteristic)曲线,计算曲线下面积(area under curve,AUG).结果 最终共纳入9篇文章,Meta分析结果显示,18F-FDG PET/CT对胃癌淋巴结转移诊断的合并SEN为0.51(95％ CI =0.47～0.55),合并SPE为0.92(95％ CI =0.89 ～0.94),合并+LR为5.77(95％ CI =4.38 ～7.59),合并-LR为0.54(95％ CI =0.45 ～0.64),DOR为12.71(95％ CI =8.97～ 18.01),AUC为0.8101.CT诊断的合并SEN为0.71(95％ CI=0.67～ 0.74),合并SPE为0.82(95％ CI =0.78 ～0.84),合并+LR为3.52(95％ CI=2.52 ～4.93),合并-LR为0.37(95％CI=0.32～0.44),DOR为10.73(95％ CI =7.35 ～ 15.66),AUC为0.8176.结论 18F-FDG PET/CT显像诊断胃癌淋巴结转移的灵敏度比CT低,但其特异性较好,有更高的诊断价值,可作为胃癌淋巴结转移的临床诊断方法之一.     

Assessment of PET/CT in multifocal myeloid sarcomas with loss of TET2: a case report and literature review

Myeloid sarcoma is a rare solid tumor consisting of leukemic myeloblasts and/or myeloid precursors occurring outside the blood or bone marrow. The unique site with myeloid sarcoma has been reported, the multiple sites of myeloid sarcoma have rarely been cited in the medical literature. Here we report that the unusual clinical presentation and management of myeloid sarcoma in multiple sites with PET-CT, highlighting the utility of PET-CT was useful in detecting and monitoring myeloid sarcoma. We also found that loss of TET2 and gain of 5 hmC in the case of myeloid sarcoma, indicating the mechanism for myeloid sarcoma is totally different with other hematopoietic malignancies.     

Evidence for a gene influencing the TG/HDL-C ratio on chromosome 7q32.3-qter: a genome-wide scan in the Framingham study

Some studies show that plasma triglyceride (TG) levels are a significant independent risk factor for cardiovascular disease (CVD). TG levels are inversely correlated with high density lipoprotein cholesterol (HDL-C) levels, and their metabolism may be closely interrelated. Therefore, the TG/HDL-C ratio may be a relevant CVD risk factor. Our analysis of families in the Framingham Heart Study gave a genetic heritability estimate for log(TG) of 0.40 and for log(TG/HDL-C) of 0.49, demonstrating an important genetic component for both. A 10 cM genome-wide scan for log(TG) level and log(TG/HDL-C) was carried out for the largest 332 extended families of the Framingham Heart Study (1702 genotyped individuals). The highest multipoint variance component LOD scores obtained for both log(TG) and log(TG/HDL-C) were on chromosome 7 (at 155 cM), where the results for the two phenotypes were 1.8 and 2.5, respectively. The 7q32.3-qter region contains several candidate genes. Four other regions with multipoint LOD scores greater than one were identified on chromosome 3 [LOD score for log(TG/HDL-C) = 1.8 at 140 cM], chromosome 11 [LOD score for log(TG/HDL-C) = 1.1 at 125 cM], chromosome 16 [LOD score for log(TG) = 1.5 at 70 cM, LOD score for log(TG/HDL-C) = 1.1 at 75 cM] and chromosome 20 [LOD score for log(TG/HDL-C) = 1.7 at 35 cM, LOD score for log(TG) = 1.3 at 40 cM]. These results identify loci worthy of further study.