FDG PET or PET/CT in patients with pancreatic cancer: when does it add to diagnostic CT or MRI?

ObjectiveAssess the impact of FDG-PET or PET/CT (PI) on pancreatic cancer management when added to CT or MRI (CDI).Materials and MethodsForty-nine patients underwent 79 PI exams. Discordant findings on PI and CDI were assessed for clinical impact.ResultsFifteen of 79 PI-CDI pairs were discordant. Ten of 79 PI favorably and 5 of 79 unfavorably altered management. PI favorably altered management more often when ordered for therapy monitoring compared to staging [risk ratio 13.00 (95% CI 1.77–95.30)] or restaging [risk ratio 18.5 (95% CI 2.50–137.22)].ConclusionPI favorably alters management more often when used for therapy monitoring compared to staging or restaging.     

Side-by-side reading of PET and CT scans in oncology: which patients might profit from integrated PET/CT?

Purpose Most early publications on integrated positron emission tomography/computed tomography (PET/CT) devices have reported the new scanner generation to be superior to conventional PET. However, few of these studies have analysed the situation where, in addition to PET, a current CT scan is available for side-by-side viewing. This fact is important, because combined PET/CT or a software-based fusion of the two modalities may improve diagnosis only in cases where side-by-side reading of PET and CT data does not lead to a definitive diagnosis. The aim of this study was to analyse which patients will profit from integrated PET/CT in terms of lesion characterization.Methods A total of 328 consecutively admitted patients referred for PET in whom a current CT scan was available were included in the study. The localization of all pathological PET lesions, as well as possible infiltration of adjacent anatomical structures, was assessed.Results Of 467 pathological lesions, 94.0% were correctly assessed with respect to localization and infiltration by either conventional PET alone (51.6%) or combined reading of PET and the already existing CT scans (42.4%). Hence, in only 6.0% of all lesions, affecting 6.7% of all patients, could evaluation have profited from integrated PET/CT.Conclusion We conclude that side-by-side viewing of PET and CT scans is essential, as in 42.4% of all cases, combined viewing was important for a correct diagnosis in our series. In up to 6.7% of patients, integrated PET/CT might have given additional information, so that in nearly 50% of patients some form of combined viewing of PET and CT data is needed for accurate lesion characterization.     

Indeterminate Findings on Oncologic PET/CT: What Difference Does PET/MRI Make?

Background

Positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) has become the standard of care for the initial staging and subsequent treatment response assessment of many different malignancies. Despite this success, PET/CT is often supplemented by MRI to improve assessment of local tumor invasion and to facilitate detection of lesions in organs with high background FDG uptake. Consequently, PET/MRI has the potential to expand the clinical value of PET examinations by increasing reader certainty and reducing the need for subsequent imaging. This study evaluates the ability of FDG-PET/MRI to clarify findings initially deemed indeterminate on clinical FDG-PET/CT studies.

Methods

A total of 190 oncology patients underwent whole-body PET/CT, immediately followed by PET/MRI utilizing the same FDG administration. Each PET/CT was interpreted by our institution's nuclear medicine service as a standard-of-care clinical examination. Review of these PET/CT reports identified 31 patients (16 %) with indeterminate findings. Two readers evaluated all 31 PET/CT studies, followed by the corresponding PET/MRI studies. A consensus was reached for each case, and changes in interpretation directly resulting from PET/MRI review were recorded. Interpretations were then correlated with follow-up imaging, pathology results, and other diagnostic studies.

Results

In 18 of 31 cases with indeterminate findings on PET/CT, PET/MRI resulted in a more definitive interpretation by facilitating the differentiation of infection/inflammation from malignancy (15/18), the accurate localization of FDG-avid lesions (2/18), and the characterization of incidental non-FDG-avid solid organ lesions (1/18). Explanations for improved reader certainty with PET/MRI included the superior soft tissue contrast of MRI and the ability to assess cellular density with diffusion-weighted imaging. The majority (12/18) of such cases had an appropriate standard of reference; in all 12 cases, the definitive PET/MRI interpretation proved correct. These 12 patients underwent six additional diagnostic studies to clarify the initial indeterminate PET/CT findings. In the remaining 13 of 31 cases with indeterminate findings on both PET/CT and PET/MRI, common reasons for uncertainty included the inability to distinguish reactive from malignant lymphadenopathy (4/13) and local recurrence from treatment effect (2/13).

Conclusions

Indeterminate PET/CT findings can result in equivocal reads and additional diagnostic studies. PET/MRI may reduce the rate of indeterminate findings by facilitating better tumor staging, FDG activity localization, and lesion characterization. In our study, PET/MRI resulted in more definitive imaging interpretations with high accuracy. PET/MRI also showed potential in reducing the number of additional diagnostic studies prompted by PET/CT findings. Our results suggest that whole-body PET/MRI provides certain diagnostic advantages over PET/CT, promotes more definitive imaging interpretations, and may improve the overall clinical utility of PET.

     

PET/CT: dose-escalated image fusion?

Clinical studies demonstrate a gain in diagnostic accuracy by employing combined PET/CT instead of separate CT and PET imaging. However, whole-body PET/CT examinations result in a comparatively high radiation burden to patients and thus require a proper justification and optimization to avoid repeated exposure or over-exposure of patients. This review article summarizes relevant data concerning radiation exposure of patients resulting from the different components of a combined PET/CT examination and presents different imaging strategies that can help to balance the diagnostic needs and the radiation protection requirements. In addition various dose reduction measures are discussed, some of which can be adopted from CT practice, while others mandate modifications to the existing hard- and software of PET/CT systems.     

Comparison of integrated whole-body PET/MR and PET/CT: Is PET/MR alternative to PET/CT in routine clinical oncology?

Purpose

To compare the diagnostic accuracy of whole-body PET/CT and integrated PET/MR in relation to the total scan time durations.

Methods

One hundred and twenty-three (123) patients (40 males and 83 females; mean age 59.6 years; range 20–83 years) with confirmed primary cancer and clinical suspicion of metastatic disease underwent whole-body 18F-FDG-PET/CT and 18F-FDG-PET/MR. Data acquisition was done after intravenous administration of 110–301 MBq radioactivity of 18F-FDG, and PET/MR data were acquired after the PET/CT data acquisition. The mean uptake times for PET/CT and PET/MR acquisition were 68.0 ± 8.0 and 98.0 ± 14 min, respectively. Total scan time was 20.0 and 25.0 min for whole-body PET/CT and PET/MR imaging.

Results

The reconstructed PET/CT and PET/MR data detected 333/355 (93.8 %) common lesions in 111/123 (90.2 %) patients. PET/CT and PET/MR alone detected 348/355 and 340/355 lesions, respectively. No significant (p = 0.08) difference was observed for the overall detection efficiency between the two techniques. On the other hand, a significant difference was observed between the two techniques for the detection of lung (p = 0.003) and cerebrospinal (p = 0.007) lesions. The 15 lesions identified by PET/CT only included 8 lung, 3 lymph nodes, 2 bone, and 1 each of peritoneal and adrenal gland lesions. On the other hand, 7 (6 brain metastatic lesions and 1 bone lesion) were identified by PET/MR only.

Conclusion

Integrated PET/MR is a feasible whole-body imaging modality and may score better than PET/CT for the detection of brain metastases. To further prove diagnostic utility, this technique requires further clinical validation.

     

肾上腺皮质癌的CT、MRI及PET/CT表现

目的探讨肾上腺皮质癌(ACC)的CT、MRI及~(18)F-FDG PET/CT影像学特征。方法回顾性分析经病理证实的21例ACC患者的影像学资料。CT增强扫描16例、MRI增强扫描8例、PET/CT扫描4例,分析其影像学表现。结果1)20例肿瘤单发(左侧13例、右侧7例),1例为双侧发病;直径为(10.9±3.0)cm;16例肿瘤呈分叶状,5例呈类圆形;2)CT表现:15例(15/17)平扫密度不均,2例均匀;瘤内钙化5例。16例整体呈渐进性强化方式;瘤内见血管影13例,瘤内见星芒状无明显强化区6例;假性厚壁囊肿样表现4例,内壁见壁结节样改变;边缘见包膜结构10例,呈延迟强化;3)MRI表现:8例呈T_1WI稍低、T_2WI稍高的混杂信号,DWI高信号;瘤内可见囊变5例、出血7例、瘢痕组织6例、脂质成分2例。强化方式与CT检查基本相同,对比剂扩清延迟;边缘见包膜结构6例,瘤内瘢痕组织延迟强化2例;4)PET/CT表现:4例呈FDG不均匀摄取增高,高摄取区与增强CT强化区一致,SUVmax为(7.5±4.7),假性厚壁囊肿样表现1例。结论ACC有一定的影像学特征,CT、MRI和PET/CT检查在诊断中各有优势,联合应用有助于全面反映肿瘤的病理特征。     

Diffusion-weighted MRI of lymphoma: prognostic utility and implications for PET/MRI?

Purpose

With the recent introduction of PET/MRI, we investigated whether diffusion-weighted imaging (DWI) can complement PET for predicting local treatment response in Hodgkin lymphoma.

Methods

This retrospective study included 39 patients selected from a hospital database with a histological diagnosis of Hodgkin lymphoma undergoing whole-body MRI (supplemented by DWI) and PET/CT before and after two cycles of vincristine, etoposide, prednisolone and doxorubicin (OEPA). The pretreatment volume, MRI apparent diffusion coefficient (ADC) and PET maximum standardized uptake value (SUV_max) of the largest nodal mass were determined quantitatively for evaluation of the local response following two cycles of OEPA. Quantitative pretreatment imaging biomarkers (disease volume, ADC, SUV_max) were compared between sites with an adequate and those with an inadequate response using Fisher’s exact test and Mann Whitney statistics. Multivariate models predictive of an inadequate response based on demographic/clinical features, pretreatment disease volume and SUV_max without (model 1) and with (model 2) the addition of ADC were derived and crossvalidated. The ROC area under curve (AUC) was calculated for both models using the full dataset (training) and the crossvalidation (test) data.

Results

Sites with an adequate response had a significantly lower median pretreatment ADC (1.0?×?10^?3mm²s^?1) than those with an inadequate response (1.26?×?10^?3mm²s^?1; p?<?0.01). There were no significant differences in patient demographic/clinical parameters, pretreatment SUV_max or pretreatment nodal volume between sites with inadequate and adequate response. The ROC-AUCs for prediction of an inadequate response for the training and test data for model 1 were 0.90 and 0.53, and for model 2 were 0.84 and 0.71, respectively.

Conclusion

DWI complements PET for prediction of site-specific interim response to chemotherapy.     

Whole‐body PET/MRI for colorectal cancer staging: Is it the way forward?

Magnetic resonance imaging (MRI) is presently the modality of choice for the local staging of rectal cancer, with positron emission tomography (PET) being optional for the evaluation of colorectal cancer. Indeed, previous studies have demonstrated that liver MRI using hepatocyte‐specific contrast agents can provide high diagnostic performance in the detection of colorectal cancer liver metastases. Recently, however, whole‐body PET/MRI, which can provide information regarding both anatomy and metabolism, has been introduced to clinical imaging, and studies are under way to assess whether it can improve diagnostic performance for oncologic diseases as well as provide additional information regarding the disease phenotype and biology compared to conventional imaging modalities of computed tomography (CT), PET, or MRI. This review offers a brief overview of the technical considerations of the PET/MRI system, and the current status of imaging modalities in the staging of colorectal cancer. The potential of whole‐body PET/MRI to improve the performance of colorectal cancer staging and the results of several recent studies will be discussed, and workflow considerations of whole‐body PET/MRI for patients with colorectal cancer will be addressed. Level of Evidence: 5 J. Magn. Reson. Imaging 2017;45:21–35.     

Ultrasound: Can it replace CT in the evaluation of pneumonia in pediatric age group?

Aim of the study

To evaluate the ultrasound efficiency in the assessment of pneumonia in pediatric age group compared to CT as a trial for radiation exposure reduction.