Multiphase CT scanning and different intravenous contrast media concentrations in combined F-18-FDG PET/CT: Effect on quantitative and clinical assessment

Influences on PET Quantification and Interpretation

Various factors have been identified that influence quantitative accuracy and image interpretation in positron emission tomography (PET). Through the continuous introduction of new PET technology—both imaging hardware and reconstruction software—into clinical care, we now find ourselves in a transition period in which traditional and new technologies coexist. The effects on the clinical value of PET imaging and its interpretation in routine clinical practice require careful reevaluation. In this review, we provide a comprehensive summary of important factors influencing quantification and interpretation with a focus on recent developments in PET technology. Finally, we discuss the relationship between quantitative accuracy and subjective image interpretation.

Qualitative and Quantitative Assessment of Abdominal and Pelvic CT Image Quality Using Iopromide With Different Concentrations of Iodine (300 and 370 mg I/mL)

OBJECTIVE

The purpose of this study was to analyze the quality of MDCT images obtained using iopromide with two different concentrations of iodine (300 and 370 mg I/mL) in daily clinical settings.

SUBJECTS AND METHODS

Patients from 38 hospitals in China undergoing abdominal or pelvic CT with iopromide were prospectively recruited. MDCT was performed using iopromide with an iodine concentration of 300 or 370 mg I/mL. CT quality image was graded as excellent, good, adequate, and poor. Objective indicators were the contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR). Outcomes were compared according to organ studied, tumor type (benign vs malignant), saline usage, and type of MDCT (16-MDCT vs 64-MDCT).

RESULTS

A total of 4506 patients (63.7% men) with a mean (± SD) age of 56.3 ± 14.1 years and mean body mass index (weight in kilograms divided by the square of height in meters) of 23.2 ± 3.3 were included. Iopromide with 300 mg I/mL was used for 3042 patients (67.5%), and 370 mg I/mL was used for 1464 patients (32.2%). A total of 1847 scans (41.0%) had excellent image quality, 2454 (54.5%) had good quality, 176 (3.9%) had adequate quality, and 29 (0.6%) had poor quality. No differences were noted between CT scans that did or did not use saline, 16-MDCT versus 64-MDCT scans, and 300 versus 370 mg I/mL iopromide. Variations in the CNR and SNR were noted between the two iodine concentrations with respect to other parameters examined.

CONCLUSION

Iopromide with both concentrations of iodine provided acceptable image quality, though according to CNR and SNR, one or the other may provide better quality in different situations.

Is there a role for PET-CT and SPECT-CT in pediatric oncology?

During the last decade, hybrid imaging has revolutionized nuclear medicine. Multimodal camera systems, integrating positron emission tomography (PET) or single photon emission computed tomography (SPECT) with computed tomography (CT) now combine the contrast provided by tumor-avid radioactive drugs with the anatomic precision of CT. While PET-CT to a great extent has replaced single-modality PET in adult oncology, the use of PET-CT in children has been controversial, since even the lowest dose CT protocols adds approximately 2 mSv to the radiation dose of about 4 mSv from the PET-study with F-18-fluorodeoxyglucose (F-18-FDG). The article describes the current techniques used, discusses radiation doses and gives an overview of current indications for PET-CT and SPECT-CT in children. Hybrid imaging with a tumor-avid radioactive drug provides extremely high contrast between tumor and background tissues, while the CT component helps to locate the lesion anatomically. Currently both PET-CT and SPECT-CT play a role in pediatric oncology; PET-CT using F-18-FDG particularly for staging and follow-up of lymphoma and brain cancer, bone and soft tissue sarcomas; SPECT-CT with I-123-metaiodobenzylguanidine (MIBG) for tumors of the sympathetic nervous system such as neuroblastoma and pheochromocytoma while the remaining neuroendocrine tumors are imaged with radioactively labeled somatostatin analogues. To reduce radiation dose, a low-dose CT in combination with ultrasound and/or magnetic resonance imaging for the assessment of anatomy is often preferred.

Comparison of 80 and 120 kVp contrast-enhanced CT for attenuation correction in PET/CT, using quantitative analysis and reporter assessment of PET image quality

AIM

To determine the effect of low tube voltage on positron-emission tomography (PET) image quality, quantitative analysis, and radiation dose in a combined PET/computed tomography (CT) study in patients with normal body mass index (BMI).

MATERIALS AND METHODS

One hundred and twenty-nine examinations performed in 46 patients (mean age 57 years), who had at least two separate studies were retrospectively evaluated; at least one with 120 kVp and one with 80 kVp. Three independent readers reviewed all PET images and graded the image quality. PET signal and noise were recorded on the liver, spleen, fat, bone marrow, and aorta. CT dose index (CTDI) and the dose-length product (DLP) were used for CT radiation dose estimation. A mixed-effects model analysis was used for comparison of estimated radiation dose and PET data.

RESULTS

There was a significant decrease of 15% in the radiation dose estimates between 80 and 120 kVp (DLP 946.2 ± 189 versus 1157.0 ± 236, respectively; p < 0.001). There was an increase of 12% in PET signal in the normal liver with 80 kVp. The average score of PET image quality obtained between 80 and 120 kVp was 4.85 ± 0.42 versus 4.90 ± 0.27, respectively (p = 0.47).

CONCLUSION

PET/80 kVp CT has no statistically significant difference in the PET image quality and quantitative analysis compared to PET/120 kVp and may be used in selected patients to reduce the radiation dose.

PET scan integration in lymphoma management

SUMMARY Despite a marked improvement in lymphoma treatment outcome, current prognostic models, relying on a pretreatment set of static clinical variables, appear unable to support a risk-adapted therapeutic strategy. On the other hand, functional imaging with 18F-fluoro-2-deoxy-D-glucose (FDG)-PET proved to be a reliable tool to dynamically assess tumor FDG uptake changes during and after treatment. In this article we aim to review the prognostic value of FDG-PET in all the stages of Hodgkin’s and non-Hodgkin’s lymphoma management, without the intent to address the diagnostic value of PET or to replace available consensus guidelines. In particular we focused on two critical issues: the cost–effectiveness of PET in the overall strategy of lymphoma diagnosis and treatment; and ongoing clinical trials adopting an interim PET-based strategy to modulate treatment intensity based on PET results. Finally, new trends in multimodality imaging, as well as in new radiopharmaceutical tracers, are briefly reviewed.