Whole-body 18F-FDG PET/CT in the presence of truncation artifacts.

We investigated the effect of CT truncation in whole-body (WB) PET/CT imaging of large patients, and we evaluated the efficacy of an extended field-of-view (eFOV) correction technique. METHODS: Two uniform phantoms simulating a "torso" and an "arms-up" setup were filled with (18)F-FDG/water. A third, nonuniform "body phantom was prepared with hot and cold lesions. All 3 phantoms were positioned in the center of the PET/CT gantry with >or=10% of their volume extending beyond the maximum CT FOV. An eFOV algorithm was used to estimate complete CT projections from nonlinear extrapolation of the truncated projections. CT-based attenuation correction (CT AC) of the phantom data was performed using CT images reconstructed from truncated and extended projections. For clinical validation, we processed truncated datasets from 10 PET/CT patients with and without eFOV correction. RESULTS: When using truncated CT images for CT AC, PET tracer distribution was suppressed outside the transverse CT FOV in phantom and patient studies. PET activity concentration in the truncated regions was only 10%-32% of the true value but increased to 84%-100% when using the extended CT images for CT AC. At the same time, the contour of phantoms and patients was recovered to the anatomically correct shape from the uncorrected emission images, and the apparent distortion of lesions near the maximum CT FOV was reduced. CONCLUSION: Truncation artifacts in WB PET/CT led to visual and quantitative distortions of the CT and attenuation-corrected PET images in the area of truncation. These artifacts can be corrected to improve the accuracy of PET/CT for diagnosis and therapy response evaluation.     

A JAFROC study of nodule detection performance in CT images of a thorax acquired during PET/CT

PurposeTwo types of CT images (modalities) are acquired in PET/CT: for attenuation correction (AC) and diagnosis. The purpose of the study was to compare nodule detection and localization performance between these two modalities.MethodsCT images, using both modalities, of an anthropomorphic chest phantom containing zero or more simulated spherical nodules of 5, 8, 10 and 12 mm diameters and contrasts −800, −630 and 100 HU were acquired. An observer performance study using nine observers interpreting 45 normal (zero nodules) images and 47 abnormal images (1–3 nodules; average 1.26) was conducted using the free-response receiver operating characteristic (FROC) paradigm. Data were analysed using an R software package implemented jackknife alternative FROC (JAFROC) analysis. Both empirical areas under the equally weighted AFROC curve (wAFROC) and under the highest rating inferred ROC (HR-ROC) curve were used as figures of merit (FOM). To control the probability of Type I error test alpha was set at 0.05.ResultsNodule detection as measured by either FOM was significantly better on the diagnostic quality images (2nd modality), irrespective of the method of analysis, [reader averaged inter-modality wAFROC FOM difference = −0.07 (−0.11,−0.04); reader averaged inter-modality HR-ROC FOM difference = −0.05 (−0.09, −0.01)].ConclusionNodule detection was statistically worse on images acquired for AC; suggesting that images acquired for AC should not be used to evaluate pulmonary pathology.     

Compressive sensing-based interior tomography: preliminary clinical application

Compressive sensing (CS)-based interior tomography is a state-of-the-art method for accurate image reconstruction from only locally truncated projections. Here, we report our preliminary interior tomography results reconstructed from raw projections of a patient acquired on a GE Discovery CT750 HD scanner. This is the first clinical application of the CS-based interior reconstruction techniques, and the results show an excellent match with those reconstructed from global projections.     

多模型自适应统计迭代重建算法对鼻窦CT图像质量和辐射剂量影响的实验研究

目的探讨鼻窦CT扫描中,前置和后置自适应统计迭代重建算法(ASiR-V)对图像质量和辐射剂量的影响,并寻找最佳的迭代组合。方法以1具离体头颅标本为研究对象,采用临床鼻窦CT常规扫描条件[噪声指数(NI)=8],以及前置ASiR-V的不同等级(0~100%,间隔为10%)进行螺旋扫描,所得原始数据使用后置ASiR-V的不同等级(0~100%,间隔为10%)进行骨算法和标准算法重建,共获得242个鼻窦薄层图像序列。选择特定的感兴趣区(ROI)测量CT值,并计算图像对比噪声比(CNR)和品质因子(FOM)。记录容积CT剂量指数(CTDIvol)和智能毫安(Smart mA)值。采用线性回归分析对ASiR-V各等级与对应的CTDIvol、Smart mA、CNR、FOM进行比较分析。采用配对t检验对相同后置不同前置ASiR-V骨算法和标准算法图像的CNR进行分析比较。主观评价采用双盲法由3名高年资放射诊断医师以4分法(4分为最佳)进行图像质量评分。结果随着前置ASiR-V等级(0~100%)的增加,Smart mA、CTDIvol均减低,呈线性负相关(r分别为-0.981、-0.976,P均<0.001);Smart mA降幅为72.05%,CTDIvol降幅为71.22%。前置ASiR-V相同,随后置ASiR-V等级增加,骨算法和标准算法图像对应的CNR呈上升趋势,呈正相关(骨算法图像:R2分别为0.976、0.992、0.982、0.982、0.975、0.975、0.979、0.996、0.952、0.978、0.965;标准算法图像:R2分别为0.944、0.990、0.988、0.993、0.996、0.987、0.984、0.996、0.996、0.990、0.965);后置ASiR-V相同,随前置ASiR-V等级增加,骨算法和标准算法图像对应的FOM呈波动变化(骨算法图像:R2分别为0.335、0.341、0.344、0.364、0.385、0.405、0.418、0.429、0.455、0.474、0.516;标准算法图像:R2分别为0.223、0.278、0.327、0.285、0.309、0.329、0.325、0.346、0.360、0.390、0.380)。以上各种前置和后置迭代等级组合所得图像主观评价均可满足诊断要求(评分≥3)。结论当NI=8时,骨算法最佳前置和后置迭代等级组合为80%和100%;标准算法最佳迭代等级组合为100%和100%。鼻窦CT扫描中,选择恰当的前置和后置迭代等级组合,能够在图像质量满足诊断要求的前提下,有效降低辐射剂量。     

Reconstruction from truncated projections using mixed extrapolations of exponential and quadratic functions

In computer tomography (CT), truncated projections are produced due to scanning large objects with a detector that is limited in width. Applying filtered back-projection(FBP) method directly to truncated projections, the reconstructed image will contain truncation artifacts - bright rings on the boundary of region of interest (ROI). Extrapolation algorithms can be used to reduce the truncation artifacts; however extrapolations are usually double the length of the projection data; resulting in an increased calculation time. This paper introduces mixed extrapolation, which is a combination of exponential and quadratic extrapolation. It is proven that doubling the length of the projection data for the mixed extrapolation can be avoided. The projections were extrapolated according to the boundary values and their derivatives. The algorithm achieves equivalence to the extrapolation approach with negligible increased calculation time. Supplementary functions are introduced in order to simplify the calculations. These functions can be calculated prior to extrapolation process, hence the calculation time is significantly reduced. The calculation times are compared between fast extrapolation introduced in this paper and normal extrapolation with doubling the length of projection data.     

双能量CT Moidal非线性图像融合技术对CT图像质量的影响

目的 比较双能量CT线性融合与Moidal非线性融合图像处理技术的差别,评价二者对CT图像质量的影响.方法 将5支试管装有不同浓度的碘对比剂溶液(16.3、26.4、48.7、74.6和112.3 HU),嵌入新鲜猪肝制成模型.扫描后由双能量扫描模式自动生成线性融合图像,Syngo工作站双能量优化对比软件重组获得Moidal非线性融合图像.按120 kV、线性融合、Moidal非线性融合分3组,分别测量并计算各组对比信噪比,采用one-wayANOVA法比较组间优良指数值差别.选取临床20例腹部双源CT扫描患者图像,分别测量并计算肝脏、肾皮质、脾脏、胰腺以及腹主动脉的信噪比,采用独立样本t检验比较线性融合与Moidal非线性融合组差别.2名观察者盲法评价2组图像各器官醒目度.结果 实验CT值为16.3、26.4、48.7、74.6和112.3 HU时,Moidal非线性融合组图像的优良指数值分别为20.65±8.18、11.40±4.25、1.60±0.82、2.40±1.13、45.49±17.86.在74.6、112.3 HU时,Moidal非线性融合组与线性融合组(分别为0.30±0.06、14.43±4.59)、120 kV组(分别为0.22±0.05、15.31±5.16)比较差异均有统计学意义,Moidal非线性融合组优良指数更高(P＜0.05).患者实质脏器比较中,Moidal非线性融合组肾实质、腹主动脉信噪比分别为19.2±5.1和36.5±13.9,线性融合组分别为12.4±3.8和22.6±7.0,差异有统计学意义(P＜0.05).2名观察者对Moidal非线性融合组各器官醒目度评分高于线性融合法(Kappa=0.64),两者一致性较好.结论 Moidal非线性融合法在提高图像信噪比、增加主观醒目度等方面明显优于线性融合法.

Abstract：

Objective To compare the difference between linear blending and non-linear blending function for dual-energy CT, and to evaluate the effect on CT image quality. Methods The model was made of a piece of fresh pork liver inserted with 5 syringes containing various concentrations of iodine solutions ( 16.3,26.4,48.7,74.6 and 112.3 HU). Linear blending images were automatically reformatted after the model was scanned in the dual-energy mode. Non-linear blending images were reformatted using the software of optimal contrast in Syngo workstation. Images were divided into 3 groups, including linear blending group, non-linear blending group and 120 kV group. Contrast noise ratio (CNR) were measured and calculated respectively in the 3 groups and the different figure of merit (FOM) values between the groups were compared using one-way ANOVA. Twenty patients scanned in the dual-energy mode were randomly selected and the SNR of their liver, renal cortex, spleen, pancreas and abdominal aorta were measured. The independent sample t test was used to compare the difference of signal to noise ratio (SNR) between linear blending group and non linear blending group. Two readers' agreement score and single-blind method were used to investigate the conspicuity difference between linear blending group and non linear blending group.Results With models of different CT values, the FOM values in non-linear blending group were 20. 65 ±8.18,11.40±4.25, 1.60±0.82,2.40±1.13, 45.49±17. 86. In 74. 6 HU and 112. 3 HU models, the differences of the FOM values observed among the three groups were statistically significant ( P＜0.05),which were 0.30±0. 06 and 14. 43 ±4. 59 for linear blending group, and 0. 22 ±0. 05 and 15.31±5.16 for 120 kV group. And non-linear blending group had a better FOM value. The SNR of renal cortex and abdominal aorta were 19.2±5.1 and 36. 5 ± 13.9 for non-linear blending group, while they were 12.4 ±3.8 and 22.6±7.0 for linear blending group. There were statistically significant differences between the two groups. The conspicuity scores of different organs in non linear blending group were far higher than those in the linear bending group. The Kappa value was 0. 64, showing good consistency. Conclusion Compared to the linear blending method, the non-linear blending method was a better option, especially in improving SNR and conspicuity.     

低辐射剂量肝脏CT增强扫描：80kVp结合迭代重建技术的初步研究

目的：探讨80 kVp管电压结合迭代重建技术（SAFIRE）在正常体重人群肝脏CT增强扫描中应用的可行性。方法：前瞻性地对身体质量指数（BMI）18～24 kg／m2、临床怀疑肝脏疾病的46例患者采用低辐射剂量（80 kVp、420 mAs）进行CT增强扫描,对比剂注射采用个性化方案。以滤波反投影法（FBP）和5种强度SAFIRE（1～5）方法分别进行图像重建。图像质量的客观评估指标：图像噪声、对比噪声比（CNR）、品质指数（FOM）。图像质量的主观评估：对图像噪声、血管显示、伪影及图像整体质量进行主观评分,并对动脉晚期的期相进行评估。结果：图像质量客观评估结果：SAFIRE-5图像的噪声最小,CNR及 FOM 值最高,与其余5组图像间差异均有统计学意义（P＜0．05）。图像质量主观评估结果：SAFIRE-5图像的噪声、血管显示情况及硬化伪影的评估结果均优于其它5组,但“蜡样”伪影的评分明显低于其它各组,使其图像整体评分受到影响;SAFIRE-3图像的整体评分最高,与其它各组间差异有统计学意义;95．6％（44／46）的动脉晚期图像质量合格。结论：正常体型人群行肝脏CT增强扫描时,使用80kVp结合迭代重建技术及个性化对比剂注射方案,能得到较好的图像质量;此种条件下,建议使用SAFIRE-3进行图像重建。     

CT管电压对鼻窦图像质量和辐射剂量的影响研究

目的探讨CT管电压在鼻窦扫描中对图像质量和辐射剂量的影响。方法利用离体头颅标本,在逐层扫描方式下,分别选择5种不同的管电压(70、80、100、120、140 kV),对鼻窦区域进行扫描。噪声指数(NI)厂家默认为9,自动管电流调制,Smart mA设置为对应管电压下的最大范围。探测器宽度为120 mm。进行骨算法和软组织算法重建,层厚均为0.625 mm。按照临床实践的基线重组横断面、冠状面和矢状面图像,层厚2 mm。在横断面的中心层面上,选择相应的兴趣区测量CT值均值和标准差,计算对比度噪声比(CNR)。同时记录CT容积剂量指数(CTDIvol)和剂量长度乘积(DLP),并计算图像品质因子(FOM)。两名放射诊断医师和1名主管技师采用双盲法对实验所得图像进行主观评价,5分制标准计分。结果实验所得影像质量均满足诊断要求。在骨算法重建下,管电压为100和80 kV的CNR分别为66.98、64.75,高于管电压为70、120、140 kV的CNR值(51.61、61.56、57.76)。CTDIvol最大值为34.11 mGy(140 kV),最小值为17.45 mGy(70 kV)。管电压100 kV时的FOM值为152.26。在软组织算法重建下,管电压为80 kV的CNR为195.62,显著高于管电压为70、100、120、140 kV组(139.46、154.49、148.06、155.58)。管电压80 kV时的FOM值为1273.56,显著高于管电压为70、100、120、140 kV组(1114.56、809.98、735.63、709.62)。结论CT头颅标本鼻窦逐层扫描中,临床怀疑骨质病变时,优先选择骨算法100 kV;临床怀疑软组织病变时,优先选择软组织算法80 kV时,所得的图像质量最佳且受检者辐射剂量较低。     

Digital tomosynthesis aided by low-resolution exact computed tomography

Tomosynthesis reconstructs 3-dimensional images of an object from a significantly fewer number of projections as compared with that required by computed tomography (CT). A major problem with tomosynthesis is image artifacts associated with the data incompleteness. In this article, we propose a hybrid tomosynthesis approach to achieve higher image quality as compared with competing methods. In this approach, a low-resolution CT scan is followed by a high-resolution tomosynthesis scan. Then, both scans are combined to reconstruct images. To evaluate the image quality of the proposed method, we design a new breast phantom for numerical simulation and physical experiments. The results show that images obtained by our approach are clearly better than those obtained without such a CT scan.     

A hybrid approach to reducing computed tomography metal artifacts in intracavitary brachytherapy

PURPOSE: To develop a hybrid approach to reduce computed tomography (CT) metal artifacts caused by the Fletcher-Suit applicator. METHODS AND MATERIALS: Using the acquired raw projection data, the hybrid algorithm determines the separate contributions from the metal and non-metal objects. Next, reconstructions of metal and non-metal images are separately obtained from their estimated projections. A final image is formed by appropriately combining the individual images. Phantom and patient data are used to evaluate the performance of this method. RESULTS: CT images reconstructed by use of the standard filtered-backprojection (FBP) algorithm contain significant artifacts even for small metal objects. However, images reconstructed using the hybrid algorithm contain virtually no artifacts. For metal objects with complex structures, the hybrid algorithm can also yield images containing fewer severe streak artifacts than those reconstructed using the FBP algorithm alone. CONCLUSIONS: These studies demonstrate that the hybrid approach can effectively reduce CT metal artifacts caused by the Fletcher-Suit applicator.     

Software correction of scatter coincidence in positron CT

This paper describes a software correction of scatter coincidence in positron CT which is based on an estimation of scatter projections from true projections by an integral transform. Kernels for the integral transform are projected distributions of scatter coincidences for a line source at different positions in a water phantom and are calculated by Klein-Nishina's formula. True projections of any composite object can be determined from measured projections by iterative applications of the integral transform. The correction method was tested in computer simulations and phantom experiments with Positologica. The results showed that effects of scatter coincidence are not negligible in the quantitation of images, but the correction reduces them significantly.     

Projection extension for region of interest imaging in cone-beam CT

RATIONALE AND OBJECTIVES: For 3D X-ray imaging during interventions, changes of the imaged object are often restricted to a small part of the field of view, suggesting region of interest (ROI) imaging by irradiating this area only. In this article, we present a novel method for extension of truncated projections in order to avoid truncation artifacts in C-arm based 3D ROI imaging. MATERIALS AND METHODS: The method makes use of prior knowledge by combining forward projections of a previously acquired, nontruncated 3D reference image with the truncated ROI projections. Rigid registration between the two datasets is achieved by using a technique based on local cross-correlation. To account for a gray value mismatch between the two data sets due to, e.g., differing beam quality and different contributions of scattered radiation, a linear gray level transformation is applied to the forward-projected reference data. RESULTS: The performance of different gray value transformation schemes is systematically assessed by means of numerical simulations. For various simulated scenarios, the best performing transformation has been identified, providing practical guidelines for selecting a scheme depending on the origin of the gray-level mismatch. Experiments prove the high performance of the developed method. CONCLUSION: The presented technique enables almost artifact-free 3D ROI imaging during interventions. This actually allows for repeated scans at low dose and enables intraprocedural imaging of large objects even with a small detector. However, applicability of the method is limited to scenarios where direct access to a reference image, e.g., a prior CT scan, is available.     

Image Quality and Lesion Detectability of Lower-Dose Abdominopelvic CT Obtained Using Deep Learning Image Reconstruction

ObjectiveTo evaluate the image quality and lesion detectability of lower-dose CT (LDCT) of the abdomen and pelvis obtained using a deep learning image reconstruction (DLIR) algorithm compared with those of standard-dose CT (SDCT) images.Materials and MethodsThis retrospective study included 123 patients (mean age ± standard deviation, 63 ± 11 years; male:female, 70:53) who underwent contrast-enhanced abdominopelvic LDCT between May and August 2020 and had prior SDCT obtained using the same CT scanner within a year. LDCT images were reconstructed with hybrid iterative reconstruction (h-IR) and DLIR at medium and high strengths (DLIR-M and DLIR-H), while SDCT images were reconstructed with h-IR. For quantitative image quality analysis, image noise, signal-to-noise ratio, and contrast-to-noise ratio were measured in the liver, muscle, and aorta. Among the three different LDCT reconstruction algorithms, the one showing the smallest difference in quantitative parameters from those of SDCT images was selected for qualitative image quality analysis and lesion detectability evaluation. For qualitative analysis, overall image quality, image noise, image sharpness, image texture, and lesion conspicuity were graded using a 5-point scale by two radiologists. Observer performance in focal liver lesion detection was evaluated by comparing the jackknife free-response receiver operating characteristic figures-of-merit (FOM).ResultsLDCT (35.1% dose reduction compared with SDCT) images obtained using DLIR-M showed similar quantitative measures to those of SDCT with h-IR images. All qualitative parameters of LDCT with DLIR-M images but image texture were similar to or significantly better than those of SDCT with h-IR images. The lesion detectability on LDCT with DLIR-M images was not significantly different from that of SDCT with h-IR images (reader-averaged FOM, 0.887 vs. 0.874, respectively; p = 0.581).ConclusionOverall image quality and detectability of focal liver lesions is preserved in contrast-enhanced abdominopelvic LDCT obtained with DLIR-M relative to those in SDCT with h-IR.     

Preliminary report on virtual monochromatic spectral imaging with fast kVp switching dual energy head CT: comparable image quality to that of 120-kVp CT without increasing the radiation dose

Purpose

This study aimed to evaluate whether the image quality of virtual monochromatic spectral imaging with fast kVp switching dual-energy CT (DECT) can be comparable to that of 120-kVp single-energy CT (SECT) without increasing the radiation dose.

Materials and methods

We retrospectively identified 15 postoperative patients who had undergone both DECT and 120-kVp SECT within a short period of time for follow-up after brain surgery. Simulated 65 keV monochromatic images were reconstructed from DECT data. Subjective image noise, gray–white matter contrast, and overall image quality were rated using a four-point scale. Quantitative measurement of noise, contrast-to-noise ratio (CNR), and posterior fossa beam-hardening artifact were also performed. The figure of merit (FOM), calculated as CNR²/CTDI_vol, was used to quantify image quality improvement per exposure risk.

Results

The mean CTDI_vol was 70.2 ± 0.3 mGy for DECT, which was 11 % lower than SECT (78.9 ± 2.1 mGy). All images were graded above clinically acceptable. Quantitative and qualitative measures for simulated 65-keV images were comparable with SECT images, except for increase in subjective noise. FOM was significantly greater for simulated 65-keV images (P = .03).

Conclusion

Our results indicate that virtual monochromatic imaging possibly provides comparable image quality to that afforded by 120-kVp SECT without increasing the dose in routine head CT.     

Androgen deprivation therapy influences the uptake of 11C-choline in patients with recurrent prostate cancer: the preliminary results of a sequential PET/CT study

Purpose

The influence of androgen deprivation therapy (ADT) on ¹¹C-choline uptake in patients with prostate cancer (PC) has not yet been clarified. The aim of our study was to investigate this issue by means of sequential ¹¹C-choline positron emission tomography (PET)/CT in patients with recurrent PC.

Methods

We retrospectively studied 14 recurrent PC patients (mean age 67?years, range 55?C82) during follow-up after radical prostatectomy (RP) with rising serum prostate-specific antigen (PSA) levels. All patients had undergone at least two consecutive ¹¹C-choline PET/CT scans: the first ¹¹C-choline PET/CT before commencing ADT and the second ¹¹C-choline PET/CT after 6?months of ADT administration.

Results

The mean serum PSA level before ADT was 17.0?±?44.1?ng/ml. After 6?months of ADT administration the PSA value significantly decreased in comparison to baseline (PSA?=?2.4?±?3.1?ng/ml, p?11C-choline PET/CT for metastatic spread, while after 6?months of ADT administration in 9 of 14 patients ¹¹C-choline PET/CT became negative.

Conclusion

These preliminary results suggest that ADT significantly reduces ¹¹C-choline uptake in androgen-sensitive PC patients.     

Image-guided radiotherapy using a mobile kilovoltage x-ray device.

A mobile isocentric C-arm kilovoltage imager has been evaluated as a potential tool for image-guided radiotherapy. The C-arm is equipped with an amorphous silicon flat panel for high-quality image acquisition. Additionally, the device is capable of cone beam computed tomography (CT) and volumetric reconstruction. This is achieved through the application of a modified Feldkamp algorithm with acquisition over a 180 degrees scan arc. The number of projections can be varied from 100 to 1000, resulting in a reconstructed volume 20 cm in diameter by 15-cm long. While acquisition time depends upon number of projections, acceptable quality images can be obtained in less than 60 seconds. Image resolution and contrast of cone-beam phantom images have been compared with images from a conventional CT scanner. The system has a spatial resolution of > or = 10 lp/cm and resolution is approximately equal in all 3 dimensions. Conversely, subject contrast is poorer than conventional CT, compromised by the increased scatter and underlying noise inherent in cone beam reconstruction, as well as the absence of filtering prior to reconstruction. The mobility of the C-arm makes it necessary to determine the C-arm position relative to the linear accelerator isocenter. Two solutions have been investigated: (1) the use of fiducial markers, embedded in the linac couch, that can subsequently be registered in the image sets; and (2), a navigation approach for infrared tracking of the C-arm relative to the linac isocenter. Observed accuracy in phantom positioning ranged from 1.0 to 1.5 mm using the navigation approach and 1.5 to 2.5 mm using the fiducial-based approach. As part of this work, the impact of respiratory motion on cone-beam image quality was evaluated, and a scheme for retrospective gating was devised. Results demonstrated that kilovoltage cone beam CT provides spatial integrity and resolution comparable to conventional CT. Cone-beam CT studies of patients undergoing radiotherapy have demonstrated acceptable soft tissue contrast, allowing assessment of daily changes in target anatomy. Of the 2 approaches developed to register images to the linac isocenter, the navigation method demonstrated superior accuracy for daily patient positioning relative to the fiducial-based method. Finally, significant image degradation due to respiratory motion was observed. It was demonstrated that this could be improved by correlating the acquisition of individual 2D projections with respiration for retrospective reconstruction of phase-based volumetric datasets.     

Virtual reality for simulation of radiographic projections: validation of projection geometry

OBJECTIVE: To develop a software for virtual reality (VR) simulation of X-ray images based on perspective projections through a patient model derived from data from a CT examination and to evaluate the accuracy in the projection geometry obtained by the software. METHODS: A VR software was developed on a personal computer, with models of a patient, an X-ray machine and a detector. The model of the patient was derived from data from a CT examination of a dry skull. Simulated radiographic images of the patient model could be rendered as perspective projections based on the relative positions between the models. The projection geometry of the software was validated by developing an artificial CT data set containing high attenuation points as objects to be imaged. The accuracy in projection geometry was evaluated in a systematic way. The distances between two dots, representing the projected test points in the simulated radiographic images, were measured. They were compared with theoretical calculations of the corresponding distances using traditional mathematical tools. RESULTS: The difference between the simulated and calculated projected distances never exceeded 0.5 mm. The error in simulated projected distances was in most cases within 1%. No systematic errors were revealed. CONCLUSION: The software, developed for personal computers, can produce simulated X-ray images with high geometric accuracy based on perspective projections through a CT data set. The software can be used for simulation of radiographic examinations.     

Impact of long-term androgen deprivation therapy on PSMA ligand PET/CT in patients with castration-sensitive prostate cancer

Purpose

Since the introduction of PSMA PET/CT with ⁶⁸Ga-PSMA-11, this modality for imaging prostate cancer (PC) has spread worldwide. Preclinical studies have demonstrated that short-term androgen deprivation therapy (ADT) can significantly increase PSMA expression on PC cells. Additionally, retrospective clinical data in large patient cohorts suggest a positive association between ongoing ADT and a pathological PSMA PET/CT scan. The present evaluation was conducted to further analyse the influence of long-term ADT on PSMA PET/CT findings.

Methods

A retrospective analysis was performed of all 1,704 patients who underwent a ⁶⁸Ga-PSMA-11 PET/CT scan at our institution from 2011 to 2017 to detect PC. Of 306 patients scanned at least twice, 10 had started and continued ADT with a continuous clinical response between the two PSMA PET/CT scans. These ten patients were included in the current analysis which compared the tracer uptake intensity and volume of PC lesions on PSMA PET/CT before and during ongoing ADT.

Results

Overall, 31 PC lesions were visible in all ten patients before initiation of ADT. However, during ongoing ADT (duration 42–369 days, median 230 days), only 14 lesions were visible in eight of the ten patients. The average tracer uptake values decreased in 71% and increased in 12.9% of the PC lesions. Of all lesions, 33.3% were still visible in six patients with a complete PSA response (≤0.1 ng/ml).

Conclusion

Continuous long-term ADT significantly reduces the visibility of castration-sensitive PC on PSMA PET/CT. If the objective is visualization of the maximum possible extent of disease, we recommend referring patients for PSMA PET/CT before starting ADT.

     

Reduction of computed tomography metal artifacts due to the Fletcher-Suit applicator in gynecology patients receiving intracavitary brachytherapy

PURPOSE: To evaluate a method of reducing computed tomography (CT) metal artifacts due to the Fletcher-Suit applicator. METHODS AND MATERIALS: We apply a projection-interpolation algorithm to CT images containing artifacts from the brachytherapy applicator. Regions of projection data containing the applicator are interpolated, removing the metal from the projections. A new image is then reconstructed, and a pixel-by-pixel correction factor applied to the original image to reduce the severity of metal artifacts. This technique is applied to phantom and patient image data. RESULTS: Qualitative and quantitative comparisons of images produced before and after projection-interpolation show a significant reduction in metal artifacts. In patient images containing the tandem alone, this method almost completely eliminated the artifact. In slices containing both tandem and colpostats, the algorithm reduced artifacts but did not completely eliminate them. CONCLUSIONS: The projection-interpolation method can be used to reduce the severity of metal artifacts caused by the Fletcher-Suit applicator.     

The effect of androgen deprivation therapy on 68 Ga-PSMA tracer uptake in non-metastatic prostate cancer patients

To evaluate the effect of neoadjuvant androgen deprivation treatment (ADT) on prostate-specific membrane antigen (PSMA) tracer uptake demonstrated in 68Ga-PSMA-positron emission tomography (PET/CT) in non-metastatic hormone-naïve prostate cancer (PC) patients. The clinical data of 108 PC patients who received neoadjuvant ADT were retrospectively analyzed. All patients had a baseline 68Ga-PSMA-PET/CT scan, and a second scan was delivered median of 2.9 months after the initiation of ADT. The maximum standardized uptake value (SUVmax) of primary tumor (SUVp) and metastatic lymph nodes (SUVln) as well as PSA response were assessed between pre- and post-ADT 68Ga-PSMA-PET/CT scans. There were significant decreases in posttreatment serum PSA, SUVp, and SUVln. A decrease in SUVp was seen in 91 patients (84%) with a median value of 66% (range, 5–100%), while 17 patients (16%) had no change in or an increase in PSMA tracer uptake with a median value of 24% (range, 0–198%). Patients with Gleason score (GS) of 7 had significantly higher metabolic response rates compared to other patients. The disease progression was significantly higher only in patients with GS > 7 disease compared to GS 7 disease. The PSA response to ADT was the lowest in patients with ISUP high-grade tumors. A total of 16 patients (15%) had progressive disease, and in 9 patients (8%), radiotherapy decisions were modified according to posttreatment 68Ga-PSMA-PET/CT scans. The current study includes the largest number of patients analyzed to date and demonstrates that ADT causes a significant decrease in serum PSA values and SUVp and SUVln. The authors demonstrate that 68Ga-PSMA-PET/CT may be used as a quantitative imaging modality after neoadjuvant ADT in hormone-naïve non-metastatic PC patients.