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.

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 McNemaŕs 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.

[Imaging procedures for gastrointestinal stromal tumors]

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.

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.

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.