Correlation of the apparent diffusion coefficient (ADC) with the standardized uptake value (SUV) in hybrid 18F-FDG PET/MRI in non-small cell lung cancer (NSCLC) lesions: initial results.

PURPOSE: To compare the apparent diffusion coefficient (ADC) in non-small cell lung cancer lesions with standardized uptake values (SUV) derived from combined 18F-fluoro-deoxy-glucose-positron emission tomography/magnetic resonance imaging (FDG-PET/MRI) and those derived from FDG-PET/CT. MATERIALS AND METHODS: In 18 consecutive patients with histologically proven NSCLC (17 men, 1 woman; mean age, 61 ± 12 years), whole-body FDG-PET/MRI was performed after whole-body FDG-PET/CT. Regions of interest (ROI) encompassing the entire primary tumor were drawn into FDG-PET/CT and FDG-PET/MR images to determine the maximum and mean standardized uptake value (SUVmax; SUVmean) and into ADC parameter maps to assess mean ADC values. Pearson's correlation coefficients were calculated to compare SUV and ADC values. RESULTS: The SUVmax of NSCLC was 12.3 ± 4.8 [mean ±SD], and the SUVmean was 7.2 ± 2.8 as assessed by FDG-PET/MRI. The SUVmax and SUVmean derived from FDG-PET/CT and FDG-PET/MRI correlated well (R = 0.93; p < 0.001 and R = 0.92; p < 0.001, respectively). The ADCmean of the pulmonary tumors was 187.9 ± 88.8 × 10-5 mm²/s [mean ± SD]. The ADCmean exhibited a significant inverse correlation with the SUVmax (R = -0.72; p < 0.001) as well as with the SUVmean assessed by FDG-PET/MRI (R = -0.71; p < 0.001). CONCLUSION: This simultaneous PET/MRI study corroborates the assumed significant inverse correlation between increased metabolic activity on FDG-PET and restricted diffusion on DWI in NSCLC.Citation Format:

Positron emission tomography (PET) attenuation correction artefacts in PET/CT and PET/MRI.

OBJECTIVE: To compare the effect of implanted medical materials on (18)F-fludeoxyglucose ((18)F-FDG) positron emission tomography (PET)/MRI using a Dixon-based segmentation method for MRI-based attenuation correction (MRAC), PET/CT and CT-based attenuation-corrected PET (PETCTAC). METHODS: 12 patients (8 males and 4 females; age 58±11 years) with implanted medical materials prospectively underwent whole-body (18)F-FDG PET/CT and PET/MRI. CT, MRI and MRAC maps as well as PETCTAC and PETMRAC images were reviewed for the presence of artefacts. Their morphology and effect on the estimation of the (18)F-FDG uptake (no effect, underestimation, overestimation compared with non-corrected images) were compared. In PETMRAC images, a volume of interest was drawn in the area of the artefact and in a reference site (contralateral body part); the mean and maximum standardised uptake values (SUVmean; SUVmax) were measured. RESULTS: Of 27 implanted materials (20 dental fillings, 3 injection ports, 3 hip prostheses and 1 sternal cerclage), 27 (100%) caused artefacts in CT, 19 (70%) in T1 weighted MRI and 17 (63%) in MRAC maps. 20 (74%) caused a visual overestimation of the (18)F-FDG uptake in PETCTAC, 2 (7%) caused an underestimation and 5 (19%) had no effect. In PETMRAC, 19 (70%) caused spherical extinctions and 8 (30%) had no effect. Mean values for SUVmean and SUVmax were significantly decreased in artefact-harbouring sites (p<0.001). CONCLUSION: Contrary to PET attenuation correction artefacts in PET/CT, which often show an overestimation of the (18)F-FDG uptake, MRAC artefacts owing to implanted medical materials in most cases cause an underestimation. ADVANCES IN KNOWLEDGE: Being aware of the morphology of artefacts owing to implanted medical materials avoids interpretation errors when reading PET/MRI.

Impact of organ-specific dose reduction on the image quality of head and neck CT angiography.

OBJECTIVES: Organ-specific dose reduction (OSDR) algorithms can reduce radiation on radiosensitive organs up to 59 %. This study evaluates the influence of a new OSDR algorithm on image quality of head and neck computed tomographic angiography (CTA) in clinical routine. METHODS: Sixty-two consecutive patients (68 ± 13 years) were randomised into two groups and imaged using 128-row multidetector CT. Group A (n = 31) underwent conventional CTA and group B (n = 31) CTA with a novel OSDR algorithm. Subjective and objective image quality were statistically compared. Subjective image quality was rated on a five-point scale. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated with region-of-interest measurements. RESULTS: The SNR of the common carotid artery and middle cerebral artery was 53.6 ± 22.7 and 43.3 ± 15.3 (group A) versus 54.1 ± 20.5 and 46.2 ± 14.6 (group B). The CNR was 40.0 ± 19.3 and 29.7 ± 12.0 (group A) compared with 40.7 ± 16.8 and 32.9 ± 10.9 (group B), respectively. Subjective image quality was excellent in both groups (mean score 4.4 ± 0.7 versus 4.4 ± 0.6). Differences between the two groups were not significant. CONCLUSIONS: The novel OSDR algorithm does not compromise image quality of head and neck CTA. Its application can be recommended for CTA in clinical routine to protect the thyroid gland and ocular lenses from unnecessary high radiation. KEY POINTS: • Organ-specific dose reduction (OSDR) can significantly reduce radiation exposure during CT • OSDR does not compromise image quality of head and neck CTA • OSDR can significantly lower the risk of radiation damage to sensitive organs • OSDR can easily be applied in routine clinical practice.

Whole-body FDG PET/CT is more accurate than conventional imaging for staging primary breast cancer patients.

PURPOSE: This retrospective study aimed (1) to compare the diagnostic accuracy of whole-body FDG PET/CT for initial breast cancer staging with the accuracy of a conventional, multimodal imaging algorithm, and (2) to assess potential alteration in patient management based on the FDG PET/CT findings. METHODS: Patients with primary breast cancer (106 women, mean age 57 ± 13 years) underwent whole-body FDG PET/CT and conventional imaging (X-ray mammography, MR mammography, chest plain radiography, bone scintigraphy and breast, axillary and liver ultrasonography). The diagnostic accuracies of FDG PET/CT and a conventional algorithm were compared. Diagnostic accuracy was assessed in terms of primary tumour detection rate, correct assessment of primary lesion focality, T stage and the detection rates for lymph node and distant metastases. Histopathology, imaging or clinical follow-up served as the standards of reference. RESULTS: FDG PET/CT was significantly more accurate for detecting axillary lymph node and distant metastases (p = 0.0125 and p < 0.005, respectively). No significant differences were detected for other parameters. Synchronous tumours or locoregional extraaxillary lymph node or distant metastases were detected in 14 patients (13%) solely by FDG PET/CT. Management of 15 patients (14%) was altered based on the FDG PET/CT findings, including 3 patients with axillary lymph node metastases, 5 patients with extraaxillary lymph node metastases, 4 patients with distant metastases and 3 patients with synchronous malignancies. CONCLUSION: Full-dose, intravenous contrast-enhanced FDG PET/CT was more accurate than conventional imaging for initial breast cancer staging due to the higher detection rate of metastases and synchronous tumours, although the study had several limitations including a retrospective design, a possible selection bias and a relevant false-positive rate for the detection of axillary lymph node metastases. FDG PET/CT resulted in a change of treatment in a substantial proportion of patients.

Radioembolization of hepatic tumors: flow redistribution after the occlusion of intrahepatic arteries.

PURPOSE: Radioembolization using 90yttrium is an emerging therapy option for unresectable liver malignancies. In order to reduce the number of yttrium injections, endovascular occlusion of a segmental hepatic artery has been proposed. The aim of this study was to assess whether sufficient vascular redistribution of the occluded liver segments through intrahepatic collaterals can be observed. MATERIALS AND METHODS: 27 patients with hepatocellular carcinoma (n = 16) or hepatic metastases (n = 11) were studied. Hepatic angiography was performed on average 16 days prior to radioembolization. The segment II/III artery (n = 9) or the segment IV artery (n = 18) was occluded using coils. Technectium-99m-labeled macroaggregated albumin (99mTc-MAA) was injected into the right and the remaining part of the left hepatic artery in order to identify any hepatic volume not included in the perfused area. Patients underwent a SPECT/CT on average 1 h after the 99mTc-MAA injection. Two radiologists evaluated the SPECT/CT scans regarding the presence of non-perfused hepatic segments. Furthermore, hepatic perfusion was assessed by digital subtraction angiography (DSA) on the day of radioembolization. RESULTS: In 16/27 patients (59%) a perfusion of the occluded liver segment was visible on the SPECT/CT scan. In 8/11 patients without flow redistribution at the time of the SPECT/CT, perfusion of the occluded segment through hepatic collaterals was observed during angiography prior to radioembolization. Hence, flow redistribution was eventually found in 24/27 patients (89%). CONCLUSION: Flow redistribution after the occlusion of intrahepatic arteries prior to radioembolization can be successfully induced in the majority of patients with anatomical variants of the hepatic arteries.

Transarterial hepatic chemoperfusion of uveal melanoma metastases: survival and response to treatment.

PURPOSE: To assess the survival of patients with hepatic uveal melanoma metastases undergoing sequential transarterial hepatic chemoperfusion. MATERIALS AND METHODS: 61 patients (mean age, 60.3 ± 13.8 y) underwent a total of 249 hepatic chemoperfusion procedures (mean: 4 chemoperfusion procedures; range, 1-7 chemoperfusion procedures; standard deviation, 2.3 chemoperfusion procedures). All patients started with melphalan. In the case of progressive disease, melphalan was replaced by a different chemoperfusion agent. 38 patients were treated with melphalan only, 23 patients were treated with a combination of melphalan and other drugs. The median overall survival time was calculated for the overall population and several sub-groups. Differences in the survival rate between the sub-groups were assessed for statistical significance. The complication rate was assessed. RESULTS: The median overall survival of the entire population was 10 months. The patients in the subgroups with a maximum number of 9 hepatic metastases as well as the patients in the subgroup without extrahepatic metastases at the beginning of therapy survived significantly longer than patients with more than 9 metastases/extrahepatic metastases (p = 0.019, p = 0.008). One patient (0.4%) died from liver failure after initial infusion of melphalan. CONCLUSION: Intraarterial sequential hepatic chemoperfusion offers a minimally invasive treatment in patients with hepatic uveal melanoma metastases with good survival times and an acceptable major complication rate.

[Modern CT and PET/CT imaging of the liver]. / Moderne CT- und PET/CT-Bildgebung der Leber.

Computed tomography (CT) is now widely available and represents an important and rapid method for the diagnostics of acute liver disease, characterization of focal liver lesions, planning of interventional therapy measures and postintervention control. In recent years CT has not become less important despite the increasing value of magnetic resonance imaging (MRI). By the use of different contrast medium phases good characterization of space-occupying lesions can be achieved. For the diagnostics of hepatocellular carcinoma (HCC) a triphasic examination protocol should always be implemented. The introduction of dual energy CT increased the sensitivity of imaging of hypervascularized and hypovascularized liver lesions and by the use of virtual native imaging it has become possible to avoid additional native imaging which reduces the x-ray exposition of patients. Positron emission tomography (PET) has an advantage for imaging in oncology because nearly the complete body of the patient can be screened and this is the main indication for PET/CT (whole-body staging). For purely hepatic problems 18F-fluorodeoxyglucose (FDG)-PET/CT using diagnostic CT data has a higher precision than CT alone but is inferior to MRI.

Diagnostic accuracy of fused positron emission tomography/magnetic resonance mammography: initial results.

OBJECTIVES: The aim of this study was to evaluate the diagnostic accuracy of fused fluoro-deoxy-D-glucose positron emission tomography/magnetic resonance mammography (FDG-PET/MRM) in breast cancer patients and to compare FDG-PET/MRM with MRM. METHODS: 27 breast cancer patients (mean age 58.9±9.9 years) underwent MRM and prone FDG-PET. Images were fused software-based to FDG-PET/MRM images. Histopathology served as the reference standard to define the following parameters for both MRM and FDG-PET/MRM: sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy for the detection of breast cancer lesions. Furthermore, the number of patients with correctly determined lesion focality was assessed. Differences between both modalities were assessed by McNemars test (p<0.05). The number of patients in whom FDG-PET/MRM would have changed the surgical approach was determined. RESULTS: 58 breast lesions were evaluated. The sensitivity, specificity, PPV, NPV and accuracy were 93%, 60%, 87%, 75% and 85% for MRM, respectively. For FDG-PET/MRM they were 88%, 73%, 90%, 69% and 92%, respectively. FDG-PET/MRM was as accurate for lesion detection (p = 1) and determination of the lesions' focality (p = 0.7722) as MRM. In only 1 patient FDG-PET/MRM would have changed the surgical treatment. CONCLUSION: FDG-PET/MRM is as accurate as MRM for the evaluation of local breast cancer. FDG-PET/MRM defines the tumours' focality as accurately as MRM and may have an impact on the surgical treatment in only a small portion of patients. Based on these results, FDG-PET/MRM cannot be recommended as an adjunct or alternative to MRM.

[Selective internal radiotherapy (SIRT) for hepatocellular carcinoma]. / Selektive interne Radiotherapie (SIRT) beim hepatozellulären Karzinom.

Microsphere-based radioembolization represents a new generation of therapeutics in interventional oncology. The intrahepatic application of radioactive microspheres via the hepatic artery allows locoregional therapy of diffuse or multifocal liver tumors, for which to date systemic therapy was the only remaining option. The current standard for this selective internal radiotherapy or radioembolization is yttrium-90 glass or resin microspheres. This review discusses the indications, the technique, and the therapeutic results of microsphere-based radioembolization.

Angiography-based C-arm CT for the assessment of extrahepatic shunting before radioembolization.

PURPOSE: To retrospectively assess the accuracy of angiography-based C-arm CT for the detection of extrahepatic shunting before SIRT. MATERIALS AND METHODS: 30 patients (mean age: 64+/-12 years) with hypervascularized hepatic tumors underwent hepatic angiography, coil embolization of gastrointestinal collaterals and 99mTc-macroaggregated albumin (MAA) SPECT/CT before SIRT. Before MAA injection via a microcatheter from the intended treatment position, an angiography and angiography-based C-arm CT (XperCT, Philips Healthcare) were acquired. Angiographies and XperCT were performed from 48 microcatheter positions followed by MAA injections and MAA-SPECT/CT. MAA-SPECT/CT served as the reference standard for determining the accuracy of hepatic arteriography and C-arm CT for the detection of extrahepatic shunting. RESULTS: MAA-SPECT/CT revealed extrahepatic shunting in 5 patients (17%). Hepatic arteriography yielded a true negative in 22 (73%), a false negative in 5 (17%), and an unclear result in 3 patients (10%). C-arm CT yielded a true positive in 3 (10%), true negative in 24 (80%), false positive in 1 (3%), and false negative in 2 patients (7%). The specificity and the NPV of hepatic arteriography for the detection of extrahepatic shunting were 88% and 81%, respectively. For C-arm CT the sensitivity, specificity, PPV, NPV, and accuracy for the detection of extrahepatic shunting were 60%, 96%, 75%, 92%, and 90%, respectively. CONCLUSION: C-arm CT offers additional information to angiography when assessing SIRT patients for extrahepatic shunting. More accurate detection of extrahepatic shunting may optimize the workflow in SIRT preparations by avoiding unnecessary repeat angiographies.

[Imaging procedures for gastrointestinal stromal tumors]. / Bildgebende Verfahren bei gastrointestinalen Stromatumoren.

Morphological and functional imaging methods are used for staging of gastrointestinal stromal tumors (GIST) and to follow-up GIST patients undergoing therapy. Computed tomography is the most frequently used morphological imaging procedure and has been recommended as the imaging method of choice according to current GIST guidelines. However, positron emission tomography using [(18)F]-2-fluoro-2-deoxy-D-glucose (FDG-PET) as the radiotracer has shown to be advantageous over morphological imaging procedures when assessing therapy response at an early time point. While tumor size reduction in morphological imaging typically requires time to develop, a decrease in FDG uptake can be detected as early as 24 h following therapy initiation. To overcome the limitations of size-based therapy response assessment on morphological imaging procedures, new density-based therapy response criteria have been developed and implemented for GIST. This review addresses both indications and accuracy of morphological and functional imaging modalities for GIST.

PET/CT for the staging and follow-up of patients with malignancies.

Positron emission tomography (PET) and computed tomography (CT) complement each other's strengths in integrated PET/CT. PET is a highly sensitive modality to depict the whole-body distribution of positron-emitting biomarkers indicating tumour metabolic activity. However, conventional PET imaging is lacking detailed anatomical information to precisely localise pathologic findings. CT imaging can readily provide the required morphological data. Thus, integrated PET/CT represents an efficient tool for whole-body staging and functional assessment within one examination. Due to developments in system technology PET/CT devices are continually gaining spatial resolution and imaging speed. Whole-body imaging from the head to the upper thighs is accomplished in less than 20 min. Spatial resolution approaches 2-4mm. Most PET/CT studies in oncology are performed with (18)F-labelled fluoro-deoxy-D-glucose (FDG). FDG is a glucose analogue that is taken up and trapped within viable cells. An increased glycolytic activity is a characteristic in many types of cancers resulting in avid accumulation of FDG. These tumours excel as "hot spots" in FDG-PET/CT imaging. FDG-PET/CT proved to be of high diagnostic value in staging and restaging of different malignant diseases, such as colorectal cancer, lung cancer, breast cancer, head and neck cancer, malignant lymphomas, and many more. The standard whole-body coverage simplifies staging and speeds up decision processes to determine appropriate therapeutic strategies. Further development and implementation of new PET-tracers in clinical routine will continually increase the number of PET/CT indications. This promotes PET/CT as the imaging modality of choice for working-up of the most common tumour entities as well as some of the rare malignancies.

Highly iodinated intravenous contrast material for PET/CT - a feasibility study.

PURPOSE: Intravenous contrast materials (CM) are of benefit in PET/CT imaging. However, CM may influence tracer quantification and may cause artifacts when using the CT data for PET attenuation correction. The aim of the study was to assess the feasibility of applying a highly concentrated CM (HCCM, 400 mg iodine/ml) in PET/CT in comparison to a lower concentrated CM (LCCM, 300 mg iodine/ml). MATERIALS AND METHODS: In 60 whole-body FDG PET/CT scans (30 scans each with HCCM and LCCM), tracer uptake (maximal standardized uptake value - SUVmax) and CT attenuation (Hounsfield Units) were quantified at 16 positions in different vessels and parenchyma. The number of potential PET artifacts was documented. The Mann-Whitney-Wilcoxon Test was performed for statistical assessment (p < 0.05). RESULTS: HCCM did not cause a significant increase in the SUVmax (p > 0.05) or the number of PET artifacts (p = 0.69) while simultaneously significantly increasing CT attenuation (p = 0.002) as compared to LCCM in 11 / 16 positions. CONCLUSION: The application of HCCM seems feasible in PET/CT and should be considered in future protocols.

Whole-body PET/CT-mammography for staging breast cancer: initial results.

The purpose of this study was to evaluate the feasibility and utility of a dedicated positron emission tomography (PET)/CT protocol in breast cancer patients. 40 patients with suspected recurrent breast cancer underwent whole-body PET/CT in the supine position (SP) followed by PET/CT of the breasts and axillae in the prone position (PP) using a special positioning aid. PP and SP images were compared in terms of the tumour-to-thoracic-wall distance, tumour-to-skin distance and tumour volume, diameter, density, maximal standardized uptake value (SUV(max)) and localization. The size of axillary areas, the number of intra-axillary lymph nodes, their transverse diameters, their SUV(max) and the number of distant metastases were compared between PP and SP images. Differences were tested for significance using the Student's t-test. All patients tolerated PP imaging well. Five locally recurrent breast cancers were detected, both in the SP and in the PP. Mean tumour-to-thoracic-wall distances (PP, 19 mm; SP, 8 mm; p = 0.003) and tumour-to-skin distances (PP, 10 mm; SP, 7 mm; p = 0.013) were significantly larger in the PP than in the SP. Potential thoracic wall or skin infiltration, as well as quadrant localization, were determined more easily in PP. The axillary area was wider in the PP when compared with SP (PP, 14.4 cm(2); SP, 10.6 cm(2); p<0.001). No other parameters were significantly different. In conclusion, a dedicated whole-body PET/CT examination, including PET/CT mammography, is feasible for clinical practice and may offer important information on the possible infiltration of a breast lesion into the adjacent thoracic wall and skin. Even though the axilla may be delineated more clearly in the PP, there seems to be no benefit with regard to N-staging.

[The effect of different chemoembolization materials on CT-based attenuation correction in PET/CT]. / Effekt verschiedener Chemoembolisationsmaterialien auf die CT-basierte Schwächungskorrektur der PET/CT.

PURPOSE: Primary and secondary hypervascularized liver tumors may be treated with transarterial chemoembolization (TACE). The purpose of this study was to experimentally quantify the effect of different chemoembolization materials on the PET activity concentration in PET/CT. MATERIALS AND METHODS: Different concentrations of lipiodol, tungsten, tantalum, and a different number of platinum coils embedded in a carrier substance were placed in a liver phantom. An insert filled with only the carrier substance served as the negative control. The liver phantom was placed in a body phantom. The liver phantom was filled with 63.3 KBq [18-F]-Fluor-2-deoxy-D-glucose (FDG)/ml water, the body phantom was filled with 19.7 KBq FDG/ml water. PET/CT was performed and PET attenuation correction was performed based on the CT data. We defined: Activity concentration over embolization material (kBq/ml) approximately measured activity concentration; activity concentration over negative control (kBq/ml) approximately real activity concentration. An overestimation of the activity concentration was quantified by the following ratio: Activity concentration overestimation = activity concentration over embolization material (kBq/ml)/activity concentration over negative control (kBq/ml). RESULTS: All chemoembolization materials led to an overestimation of the PET activity concentration when using CT information for PET attenuation correction. The extent of overestimation is dependent on the concentration and the density of the chemoembolizing agent. PET activity overestimation was 11-151% with lipiodol, 34-1827% with tungsten, 16-1205% with tantalum, and 4-29% with platinum coils. CONCLUSION: Conventional chemoembolization materials cause an overestimation of the PET activity concentration in CT-based attenuation-corrected PET/CT images. This is of importance for the clinical routine since activity concentration quantification may not be used in the presence of chemoembolizing agents for imaging follow-up. If an increased FDG uptake is detected after transarterial chemoembolization, non-attenuation-corrected PET images must be assessed in addition to the attenuation-corrected images in order to differentiate artificially increased tracer uptake from a true increase in activity concentration of the tracer. The use of non-attenuating chemoembolizing materials (e.g. drug-eluting beads) for TACE may serve as an alternative to avoid embolization-associated PET artifacts.