Increasing Uptake Time in FDG-PET: Standardized Uptake Values in Normal Tissues at 1 versus 3 h

Potential Clinical Impact of LAFOV PET/CT: A Systematic Evaluation of Image Quality and Lesion Detection

We performed a systematic evaluation of the diagnostic performance of LAFOV PET/CT with increasing acquisition time. The first 100 oncologic adult patients referred for 3 MBq/kg 2-[18F]fluoro-2-deoxy-D-glucose PET/CT on the Siemens Biograph Vision Quadra were included. A standard imaging protocol of 10 min was used and scans were reconstructed at 30 s, 60 s, 90 s, 180 s, 300 s, and 600 s. Paired comparisons of quantitative image noise, qualitative image quality, lesion detection, and lesion classification were performed. Image noise (n = 50, 34 women) was acceptable according to the current standard of care (coefficient-of-varianceref < 0.15) after 90 s and improved significantly with increasing acquisition time (PB < 0.001). The same was seen in observer rankings (PB < 0.001). Lesion detection (n = 100, 74 women) improved significantly from 30 s to 90 s (PB < 0.001), 90 s to 180 s (PB = 0.001), and 90 s to 300 s (PB = 0.002), while lesion classification improved from 90 s to 180 s (PB < 0.001), 180 s to 300 s (PB = 0.021), and 90 s to 300 s (PB < 0.001). We observed improved image quality, lesion detection, and lesion classification with increasing acquisition time while maintaining a total scan time of less than 5 min, which demonstrates a potential clinical benefit. Based on these results we recommend a standard imaging acquisition protocol for LAFOV PET/CT of minimum 180 s to maximum 300 s after injection of 3 MBq/kg 2-[18F]fluoro-2-deoxy-D-glucose.

Prognostic value of TLR from FDG PET/CT in patients with margin-negative stage IB and IIA non-small cell lung cancer

OBJECTIVES

To evaluate the prognostic value of TLR from PET/CT in patients with resection margin-negative stage IB and IIA non-small cell lung cancer (NSCLC) and compare high-risk factors necessitating adjuvant treatment (AT).

METHODS

Consecutive FDG PET/CT scans performed for the initial staging of NSCLC stage IB and IIA were retrospectively reviewed. The maximum standardized uptake value (SUVmax) of the primary tumor and mean SUV of the liver were acquired. The tumor-to-liver SUV ratio (TLR) was also calculated. Charts were reviewed for basic patient characteristics and high-risk factors for considering AT (poor differentiation, visceral pleura invasion, vascular invasion, tumors > 4 cm, and wedge resection). Statistical analysis was performed using Cox regression analysis and the Kaplan-Meier method.

RESULTS

Of the 112 patients included, 15 (13.4%) died, with a median overall survival (OS) of 43.8 months. Twenty-two patients (19.6%) exhibited recurrence, with median disease-free survival (DFS) of 36.0 months. In univariable analysis, pathology, poor differentiation, and TLR were associated with shorter DFS and OS. In multivariable analysis, TLR (hazard ratio [HR] = 1.263, p = 0.008) and differentiation (HR = 3.087, p = 0.012) were associated with shorter DFS. Also, TLR (HR = 1.422, p < 0.001) was associated with shorter OS.

CONCLUSION

TLR from FDG PET/CT was an independent prognostic factor for recurrence and survival. PET parameters constitute risk factors for consideration in the decision-making for AT in margin-negative stage IB and IIA NSCLC.

CLINICAL RELEVANCE STATEMENT

In this study, TLR from FDG PET/CT was an independent prognostic factor in stage IB-IIA non-small cell cancer patients. Although additional validation studies are warranted, TLR has the potential to be used to determine the need for adjuvant therapy.

KEY POINTS

• High TLR is an independent poor prognostic factor in stage IB-IIA NSCLC. • Adjuvant treatment should be considered in patients with high TLR following complete tumor resection.

Variations induced by body weight and background lesion normalization in standardized uptake value estimated by F18-FDG PET/CT

AIM

This work aims to study the impact of different SUV variants in terms of mean and maximum measures as well as various normalization methods with respect to body weight, body mass index, body surface area, and lean body mass in patients with lymphoma.

METHODS

Sixty-nine patients (34 male-35 female) were retrospectively selected. All patients had undergone F18-FDG PET/CT using the standard imaging protocol. In the first part of this study, SUVmean and SUVmax of patients' lesions and three background sites including liver, aorta, and muscle were determined. Then, the normalization of lesion SUV to body weight and body background sites was performed. The ratio of lesion SUVmax to body background sites (muscle, aorta, and liver) SUVmax was determined in addition to the ratio of lesion SUVmean to body background sites SUVmean. The second part of the study included the calculations of the body mass index (BMI), body surface area (BSA), and lean body mass (LBM). The normalization of lesion, liver, aorta, and muscle SUV to BMI, BSA, and LBM was calculated and compared to each other.

RESULTS

After performing the appropriate statistical calculations, the results showed that there is a significant difference in SUV measurements between the three background sites. Lesions normalized to the liver were significantly lower than those normalized to aorta and muscle and the results also showed a higher magnitude of lesions normalized to muscle in comparison to the aorta. The SUVmax and SUVmean normalized to different body weight indices showed the lowest variation with BSA and BMI while being increasingly higher with lean body mass using the two methods James and Janmahasatian, respectively, and then highest with body weight.

CONCLUSION

The SUVmax and SUVmean showed lower variance in comparison to other background regions. Less variation was also remarkable in SUVmean normalized to BSA and Janma lean mass and also when SUVmax is normalized to James lean body mass. The SUVmax normalized to lean (i.e., James) as well as SUVmean normalized to lean (i.e., Janma) and BSA showed a significant independence with body weight.

Intrapatient variability of 18F-FDG uptake in normal tissues

Objectives

To investigate the effect of serum glucose level and other confounding factors on the variability of maximum standardized uptake value (SUVmax) in normal tissues within the same patient on two separate occasions and to suggest an ideal reference tissue.

Materials and Methods

We retrospectively reviewed 334 18F-FDG PET/CT scans of 167 cancer patients including 38 diabetics. All patients had two studies, on average 152 ± 68 days apart. Ten matched volumes of interest were drawn on the brain, right tonsil, blood pool, heart, lung, liver, spleen, bone marrow, fat, and iliopsoas muscle opposite third lumber vertebra away from any pathological 18F-FDG uptake to calculate SUVmax.

Results

SUVmax of the lungs and heart were significantly different in the two studies (P = 0.003 and P = 0.024 respectively). Only the brain uptake showed a significant moderate negative correlation with the level of blood glucose in diabetic patients (r = −0.537, P = 0.001) in the first study, while the SUVmax of other tissues showed negligible or weak correlation with the level of blood glucose in both studies.

The liver showed significant moderate positive correlation with body mass index (BMI) in both studies (r = .416, P = <0.001 versus r = 0.453, P = <0.001, respectively), and blood pool activity showed significant moderate positive correlation with BMI in the first study only (r = 0.414, P = <0.001). The liver and blood pool activities showed significant moderate negative correlation with 18F-FDG uptake time in first study only (r = −0.405, P-value = <0.001; and r = −0.409, P-value = <0.001, respectively).

In the multivariate analysis, the liver showed a consistent effect of the injected 18F-FDG dose and uptake duration on its SUVmax on the two occasions. In comparison, spleen and muscle showed consistent effect only of the injected dose on the two occasions.

Conclusion

The liver, muscle, and splenic activities showed satisfactory test/retest stability and can be used as reference activities. The spleen and muscle appear to be more optimal reference than the liver, as it is only associated with the injected dose of 18F-FDG.

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.

Automated liver lesion detection in 68Ga DOTATATE PET/CT using a deep fully convolutional neural network

BACKGROUND

Gastroenteropancreatic neuroendocrine tumors most commonly metastasize to the liver; however, high normal background ⁶⁸Ga-DOTATATE activity and high image noise make metastatic lesions difficult to detect. The purpose of this study is to develop a rapid, automated and highly specific method to identify ⁶⁸Ga-DOTATATE PET/CT hepatic lesions using a 2D U-Net convolutional neural network.

METHODS

A retrospective study of ⁶⁸Ga-DOTATATE PET/CT patient studies (n = 125; 57 with ⁶⁸Ga-DOTATATE hepatic lesions and 68 without) was evaluated. The dataset was randomly divided into 75 studies for the training set (36 abnormal, 39 normal), 25 for the validation set (11 abnormal, 14 normal) and 25 for the testing set (11 abnormal, 14 normal). Hepatic lesions were physician annotated using a modified PERCIST threshold, and boundary definition by gradient edge detection. The 2D U-Net was trained independently five times for 100,000 iterations using a linear combination of binary cross-entropy and dice losses with a stochastic gradient descent algorithm. Performance metrics included: positive predictive value (PPV), sensitivity, F₁ score and area under the precision-recall curve (PR-AUC). Five different pixel area thresholds were used to filter noisy predictions.

RESULTS

A total of 233 lesions were annotated with each abnormal study containing a mean of 4 ± 2.75 lesions. A pixel filter of 20 produced the highest mean PPV 0.94 ± 0.01. A pixel filter of 5 produced the highest mean sensitivity 0.74 ± 0.02. The highest mean F₁ score 0.79 ± 0.01 was produced with a 20 pixel filter. The highest mean PR-AUC 0.73 ± 0.03 was produced with a 15 pixel filter.

CONCLUSION

Deep neural networks can automatically detect hepatic lesions in ⁶⁸Ga-DOTATATE PET. Ongoing improvements in data annotation methods, increasing sample sizes and training methods are anticipated to further improve detection performance.

Physiological fluorodeoxyglucose uptake of spinal cord in adults

OBJECTIVE

Physiological fluorodeoxyglucose (FDG) uptake of spinal cord needs to be correctly recognized during evaluation of whole-body PET scans, especially for oncological cases. Our aim was to analyze physiological cord FDG uptake and its relation to gender, age, body weight, environmental temperature and time to imaging.

MATERIALS AND METHODS

PET scans of 254 patients in a single year, one patient for every working day were retrospectively selected. Temperature data were obtained from meteorology recordings. Maximum standard uptake value (SUVmax) of spinal cord at cervical and lower thoracic levels were noted. Spinal canal at L5 level, cerebellum and liver were used for normalization. Correlations with age, body weight, time to imaging and environmental temperature were analyzed.

RESULTS

Cervical SUV was higher than thoracic SUV (2.5-2.3). Cervical and lower thoracic SUV's were strongly correlated, highest when corrected with L5 level vertebral canal and liver (corr coeff 0.84 and 0.75) and lowest with cerebellum (corr coeff 0.4). Cervical spinal cord FDG uptake was higher for females than males (2.6 to 2.4). Temperature and age did not change spinal cord uptake. There were weak positive correlations with body weight (corr coeff 0.16 and 0.28, cervical and thoracic). There was weak negative correlation of cervical uptake with time to imaging (corr coeff -0.17).

CONCLUSION

Spinal cord FDG uptake at cervical and lower thoracic levels are strongly correlated. Females have slightly higher cervical SUV. Age and temperature does not change spinal cord FDG uptake in adults. Cord SUV's slightly increased with body weight.

The added value of dual-time-point 18F-FDG PET/CT imaging in the diagnosis of colorectal cancer liver metastases

PURPOSE

To investigate the added value of dual-time-point ¹⁸F-FDG PET/CT imaging in the diagnosis of colorectal cancer liver metastases (CRLM).

METHODS

One hundred and eight patients with CRLM preoperatively underwent a dual-time-point ¹⁸F-FDG PET/CT scan. All hepatic lesions were diagnosed by histopathology. The diagnostic sensitivity of ¹⁸F-FDG PET/CT for CRLM was calculated on early scan and delayed scan, respectively. The McNemar test was used to test the differences of the sensitivity and the specificity between early scan and delayed scan.

RESULTS

On a per-patient basis, no significant difference in sensitivity was found between early scan and delayed scan (92.93% vs. 96.97%, P = 0.125). The per-patient specificity of early and delayed scans was 77.78%. On a per-lesion basis, overall sensitivity of delayed scan was significantly higher than that of early scan (83.49% vs. 76.61%, P < 0.001). The per-lesion specificity of early and delayed scans was 69.23%. For the lesion size of CRLM ≤ 10 mm, delayed imaging had significantly higher sensitivity than early imaging (47.17% vs. 26.42%, P < 0.001). However, for CRLM > 10 mm, there was no significant difference in sensitivity between early and delayed scans (92.73% vs. 95.15%, P = 0.125). Of the detected 182 liver metastatic lesions on delayed scan, the SUV_max on delayed scan was significantly higher than that on early scan (12.13 ± 7.13 vs. 9.16 ± 4.74, P < 0.001). The SUVmean of the normal liver on delayed scan was significantly lower than that on early scan (1.91 ± 0.29 vs. 2.33 ± 0.31, P < 0.001). The tumor to normal background ratio on delayed scan was significantly higher than that on early scan (6.59 ± 4.43 vs. 4.02 ± 2.23, P < 0.001).

CONCLUSION

The dual-time-point ¹⁸F-FDG PET/CT imaging might detect more CRLM lesions compared with single-time-point imaging, especially for small (< 10 mm) lesions.

What and how should we measure in paediatric oncology FDG-PET/CT? Comparison of commonly used SUV metrics for differentiation between paediatric tumours

Background

In clinical routine, SUV_max and SUV_peak are most often used to determine the glucose metabolism in tumours by ¹⁸F-FDG PET/CT. Both metrics can be further normalised to SUVs in reference regions resulting in a SUV ratio (SUV_ratio). The aim of the study was to directly compare several widely used SUVs/SUV_ratios with regard to differentiation between common tumours in paediatric patients; a special focus was put on characteristics of reference region SUVs.

Methods

The final study population consisted of 61 children and adolescents with diagnoses of non-Hodgkin lymphoma (NHL, n = 25), Hodgkin lymphoma (HL, n = 14), and sarcoma (n = 22). SUV metrics included SUV_max and SUV_peak as well as both parameters normalised to liver and mediastinal blood pool, respectively, yielding the SUV_ratios SUV_max/liver, SUV_{max/mediastinum}, SUV_peak/liver, and SUV_{peak/mediastinum}.

Results

The metrics SUV_max, SUV_peak, SUV_max/liver, and SUV_peak/liver all proved to be sensitive for tumour differentiation (p ≤ 0.008); in contrast, SUV_{max/mediastinum} and SUV_{peak/mediastinum} revealed to be non-sensitive approaches. Correlation analyses showed inverse associations between reference region SUVs and SUV_ratios (p < 0.05). Multiple regression analyses demonstrated significant effects of factors as bodyweight and uptake time on reference region SUVs (p < 0.01), and thus indirectly on the corresponding SUV_ratios.

Conclusions

In the paediatric population, the ability to differentiate between common tumours remarkably varies between SUV metrics. When using SUV_ratios, the choice of reference region is crucial. Factors potentially influencing reference region SUVs (and thus SUV_ratios) should be taken into account in order to avoid erroneous conclusions. When not possible, SUV_max and SUV_peak represent less complex, more robust alternatives.

Comparison between silicon photomultiplier-based and conventional PET/CT in patients with suspected lung cancer-a pilot study

Background

Lung cancer is one of the most common cancers in the world. Early detection and correct staging are fundamental for treatment and prognosis. Positron emission tomography with computed tomography (PET/CT) is recommended clinically. Silicon (Si) photomultiplier (PM)-based PET technology and new reconstruction algorithms are hoped to increase the detection of small lesions and enable earlier detection of pathologies including metastatic spread. The aim of this study was to compare the diagnostic performance of a SiPM-based PET/CT (including a new block-sequential regularization expectation maximization (BSREM) reconstruction algorithm) with a conventional PM-based PET/CT including a conventional ordered subset expectation maximization (OSEM) reconstruction algorithm. The focus was patients admitted for ¹⁸F-fluorodeoxyglucose (FDG) PET/CT for initial diagnosis and staging of suspected lung cancer. Patients were scanned on both a SiPM-based PET/CT (Discovery MI; GE Healthcare, Milwaukee, MI, USA) and a PM-based PET/CT (Discovery 690; GE Healthcare, Milwaukee, MI, USA). Standardized uptake values (SUV) and image interpretation were compared between the two systems. Image interpretations were further compared with histopathology when available.

Results

Seventeen patients referred for suspected lung cancer were included in our single injection, dual imaging study. No statically significant differences in SUV_max of suspected malignant primary tumours were found between the two PET/CT systems. SUV_max in suspected malignant intrathoracic lymph nodes was 10% higher on the SiPM-based system (p = 0.026). Good consistency (14/17 cases) between the PET/CT systems were found when comparing simplified TNM staging. The available histology results did not find any obvious differences between the systems.

Conclusion

In a clinical setting, the new SiPM-based PET/CT system with a new BSREM reconstruction algorithm provided a higher SUV_max for suspected lymph node metastases compared to the PM-based system. However, no improvement in lung cancer detection was seen.

A whole-body FDG PET/MR atlas for multiparametric voxel-based analysis

Quantitative multiparametric imaging is a potential key application for Positron Emission Tomography/Magnetic Resonance (PET/MR) hybrid imaging. To enable objective and automatic voxel-based multiparametric analysis in whole-body applications, the purpose of this study was to develop a multimodality whole-body atlas of functional 18F-fluorodeoxyglucose (FDG) PET and anatomical fat-water MR data of adults. Image registration was used to transform PET/MR images of healthy control subjects into male and female reference spaces, producing a fat-water MR, local tissue volume and FDG PET whole-body normal atlas consisting of 12 male (66.6 ± 6.3 years) and 15 female (69.5 ± 3.6 years) subjects. Manual segmentations of tissues and organs in the male and female reference spaces confirmed that the atlas contained adequate physiological and anatomical values. The atlas was applied in two anomaly detection tasks as proof of concept. The first task automatically detected anomalies in two subjects with suspected malignant disease using FDG data. The second task successfully detected abnormal liver fat infiltration in one subject using fat fraction data.

Impacts of time interval on 18F-FDG uptake for PET/CT in normal organs: A systematic review

BACKGROUND

To perform a systematic review of the effect of time interval on 2-deoxy-2-[18F] fluoro-D-glucose (18F-FDG) uptake in normal organs.

METHODS

PubMed, EMBASE, Ovid, and Cochrane databases were searched to identity all potential eligible literature. The study characteristics and relevant data were extracted and analyzed. We adopted the effect size (ES) and the coefficient of determination (R) to best measure the magnitude of the relation between time interval and 18F-FDG uptake in normal organs.

RESULTS

Seven articles and 860 participants were included. The time interval on liver and mediastinal blood pool were relatively medium (R=0.01-0.03, ES = -0.57 and -0.60) but noticeable (R = 0.06, ES = -0.68 and -0.39), respectively. The uptake of 18F-FDG on cerebellum, spleen, bone marrow, muscle, bowel, and adipose remains to be verified as the rare studies. In addition, other factors such as body mass index and blood glucose level appeared to be important which also affect 18F-FDG uptake in normal organs.

CONCLUSION

The impact of time interval on SUVs in liver and mediastinal blood pool were relatively medium but clinically noticeable. More studies need to be done to solve the relation between the SUVs of other organs and time interval.

MFN2-associated lipomatosis: Clinical spectrum and impact on adipose tissue

BACKGROUND

Multiple symmetric lipomatosis (MSL) is characterized by upper-body lipomatous masses frequently associated with metabolic and neurological signs. MFN2 pathogenic variants were recently implicated in a very rare autosomal recessive form of MSL. MFN2 encodes mitofusin-2, a mitochondrial fusion protein previously involved in Charcot-Marie-Tooth neuropathy.

OBJECTIVE

To investigate the clinical, metabolic, tissular, and molecular characteristics of MFN2-associated MSL.

METHODS

We sequenced MFN2 in 66 patients referred for altered fat distribution with one or several lipomas or lipoma-like regions and performed clinical and metabolic investigations in patients with positive genetic testing. Lipomatous tissues were studied in 3 patients.

RESULTS

Six patients from 5 families carried a homozygous p.Arg707Trp pathogenic variant, representing the largest reported series of MFN2-associated MSL. Patients presented both lipomatous masses and a lipodystrophic syndrome (lipoatrophy, low leptinemia and adiponectinemia, hypertriglyceridemia, insulin resistance and/or diabetes). Charcot-Marie-Tooth neuropathy was of highly variable clinical severity. Lipomatous tissue mainly contained hyperplastic unilocular adipocytes, with few multilocular cells. It displayed numerous mitochondrial alterations (increased number and size, structural defects). As compared to control subcutaneous fat, mRNA and protein expression of leptin and adiponectin was strikingly decreased, whereas the CITED1 and fibroblast growth factor 21 (FGF21) thermogenic markers were strongly overexpressed. Consistently, serum FGF21 was markedly increased, and ¹⁸F-FDG-PET-scan revealed increased fat metabolic activity.

CONCLUSION

MFN2-related MSL is a novel mitochondrial lipodystrophic syndrome involving both lipomatous masses and lipoatrophy. Its complex neurological and metabolic phenotype justifies careful clinical evaluation and multidisciplinary care. Low leptinemia and adiponectinemia, high serum FGF21, and increased ¹⁸F-FDG body fat uptake may be disease markers.

Comparison of PET/MRI With PET/CT in the Evaluation of Disease Status in Lymphoma

PURPOSE

The primary aim was to compare the diagnostic performance of PET/MRI (performed with basic anatomical MRI sequences) in detecting sites of disease in adult patients with lymphoma compared with the current standard of care, PET/CT. Secondary aims were to assess the additional value of diffusion-weighted imaging to PET/MRI in disease detection and to evaluate the relationship between the standardized uptake value on PET/MR and the apparent diffusion coefficient on diffusion-weighted imaging.

METHODS

Sixty-eight studies in 66 consecutive patients with histologically proven Hodgkin or non-Hodgkin lymphoma were prospectively evaluated. Each patient had whole body PET/CT, followed by whole body PET/MR. Two experienced readers independently evaluated the PET/MRI studies, and two other experienced readers independently evaluated PET/CT. Site of lymphoma involvement and SUVmax at all nodal sites more avid than background liver were recorded. Readers provided stage (in baseline cases) and disease status (remission vs active disease). The apparent diffusion coefficient mean value corresponding to the most avid PET site of disease was recorded.

RESULTS

Ninety-five nodal and 8 extranodal sites were identified on both PET/CT and PET/MRI. In addition, 3 nodal and 1 extranodal sites were identified on PET/MRI. For positive lesion detection, reader agreement in PET/MR was perfect between the 2 readers and almost perfect between PET/CT and PET/MR (k > 0.978). Intermodality agreement between PET/CT and PET/MRI was also near perfect to perfect for staging/disease status k = (0.979-1.000). SUVmax from PET/CT and PET/MRI correlated significantly (Spearman rho correlation coefficient, 0.842; P < 0.001). Diffusion-weighted imaging did not alter lesion detection or staging in any case. A negative correlation was demonstrated between ADC mean and SUVmax (Spearman rho correlation coefficient r, -0.642; P < 0.001).

CONCLUSIONS

PET/MRI is a reliable alternative to PET/CT in the evaluation of patients with lymphoma. Diffusion-weighted imaging did not alter diagnostic accuracy. With comparable accuracy in detection of disease sites and added benefit of radiation dose reduction, PET/MRI has a potential to become part of routine lymphoma imaging.

Software-based PET-MR image coregistration: combined PET-MRI for the rest of us!

BACKGROUND

With the introduction of hybrid positron emission tomography/magnetic resonance imaging (PET/MRI), a new imaging option to acquire multimodality images with complementary anatomical and functional information has become available. Compared with hybrid PET/computed tomography (CT), hybrid PET/MRI is capable of providing superior anatomical detail while removing the radiation exposure associated with CT. The early adoption of hybrid PET/MRI, however, has been limited.

OBJECTIVE

To provide a viable alternative to the hybrid PET/MRI hardware by validating a software-based solution for PET-MR image coregistration.

MATERIALS AND METHODS

A fully automated, graphics processing unit-accelerated 3-D deformable image registration technique was used to align PET (acquired as PET/CT) and MR image pairs of 17 patients (age range: 10 months-21 years, mean: 10 years) who underwent PET/CT and body MRI (chest, abdomen or pelvis), which were performed within a 28-day (mean: 10.5 days) interval. MRI data for most of these cases included single-station post-contrast axial T1-weighted images. Following registration, maximum standardized uptake value (SUVmax) values observed in coregistered PET (cPET) and the original PET were compared for 82 volumes of interest. In addition, we calculated the target registration error as a measure of the quality of image coregistration, and evaluated the algorithm's performance in the context of interexpert variability.

RESULTS

The coregistration execution time averaged 97±45 s. The overall relative SUVmax difference was 7% between cPET-MRI and PET/CT. The average target registration error was 10.7±6.6 mm, which compared favorably with the typical voxel size (diagonal distance) of 8.0 mm (typical resolution: 0.66 mm × 0.66 mm × 8 mm) for MRI and 6.1 mm (typical resolution: 3.65 mm × 3.65 mm × 3.27 mm) for PET. The variability in landmark identification did not show statistically significant differences between the algorithm and a typical expert.

CONCLUSION

We have presented a software-based solution that achieves the many benefits of hybrid PET/MRI scanners without actually needing one. The method proved to be accurate and potentially clinically useful.

Ratio of Mediastinal Lymph Node SUV to Primary Tumor SUV in 18F-FDG PET/CT for Nodal Staging in Non-Small-Cell Lung Cancer

PURPOSE

Following determination of the maximum standardized uptake values (SUVmax) of the mediastinal lymph nodes (SUV-LN) and of the primary tumor (SUV-T) on ¹⁸F-FDG PET/CT in patients with non-small-cell lung cancer (NSCLC), the aim of the study was to determine the value of the SUV-LN/SUV-T ratio in lymph node staging in comparison with that of SUV-LN.

METHODS

We retrospectively reviewed a total of 289 mediastinal lymph node stations from 98 patients with NSCLC who were examined preoperatively for staging and subsequently underwent pathologic studies of the mediastinal lymph nodes. We determined SUV-LN and SUV-R for each lymph node station on ¹⁸F-FDG PET/CT and then classified each station into one of three groups based on SUV-T (low, medium and high SUV-T groups). Diagnostic performance was assessed based on receiver operating characteristic (ROC) curve analysis, and the optimal cut-off values that would best discriminate metastatic from benign lymph nodes were determined for each method.

RESULTS

The average of SUV-R of malignant lymph nodes was significantly higher than that of benign lymph nodes (0.79 ± 0.45 vs. 0.36 ± 0.23, P < 0.0001). In the ROC curve analysis, the area under the curve (AUC) of SUV-R was significantly higher than that of SUV-LN in the low SUV-T group (0.885 vs. 0.810, P = 0.019). There were no significant differences between the AUCs of SUV-LN and of SUV-R in the medium and high SUV-T groups. The optimal cut-off value for SUV-R in the low SUV-T group was 0.71 (sensitivity 87.5 %, specificity 85.9 %).

CONCLUSIONS

The SUV-R performed well in distinguishing between metastatic and benign lymph nodes. In particular, SUV-R was found to have a better diagnostic performance than SUV-LN in the low SUV-T group.

Consistency of metabolic tumor volume of non-small-cell lung cancer primary tumor measured using 18F-FDG PET/CT at two different tracer uptake times

OBJECTIVES

The objective of this study was to test the hypothesis that the metabolic tumor volume (MTV) of primary non-small-cell lung cancer is not sensitive to differences in F-fluorodeoxyglucose (F-FDG) uptake time, and to compare this consistency of MTV measurements with that of standardized uptake value (SUV) and total lesion glycolysis (TLG).

METHODS

Under Institutional Review Board approval, 134 consecutive patients with histologically proven non-small-cell lung cancer underwent F-FDG PET/computed tomography scanning at about 1 h (early) and 2 h (delayed) after intravenous injection of F-FDG. MTV, SUV, and TLG of the primary tumor were all measured. Student's t-test and Wilcoxon's signed-rank test for paired data were used to compare MTV, SUV, and TLG between the two scans. The intraclass correlation coefficient (ICC) was used to assess agreement in PET parameters between the two scans and between the measurements made by two observers.

RESULTS

MTV was not significantly different (P=0.17) between the two scans. However, SUVmax, SUVmean, SUVpeak, and TLG increased significantly from the early to the delayed scans (P<0.0001 for all). The median percentage change between the two scans in MTV (1.65%) was smaller than in SUVmax (11.76%), SUVmean(10.57%), SUVpeak(13.51%), and TLG (14.34%); the ICC of MTV (0.996) was greater than that of SUVmax (0.933), SUVmean (0.952), SUVpeak (0.928), and TLG (0.982). Interobserver agreement between the two radiologists was excellent for MTV, SUV, and TLG on both scans (ICC: 0.934-0.999).

CONCLUSION

MTV is not sensitive to common clinical variations in F-FDG uptake time, its consistency is greater than that of SUVmax, SUVmean, SUVpeak, and TLG, and it has excellent interobserver agreement.

Evaluation of diagnostic performance of whole-body simultaneous PET/MRI in pediatric lymphoma

BACKGROUND

Whole-body (18)F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is the standard of care for lymphoma. Simultaneous PET/MRI (magnetic resonance imaging) is a promising new modality that combines the metabolic information of PET with superior soft-tissue resolution and functional imaging capabilities of MRI while decreasing radiation dose. There is limited information on the clinical performance of PET/MRI in the pediatric setting.

OBJECTIVE

This study evaluated the feasibility, dosimetry, and qualitative and quantitative diagnostic performance of simultaneous whole-body FDG-PET/MRI in children with lymphoma compared to PET/CT.

MATERIALS AND METHODS

Children with lymphoma undergoing standard of care FDG-PET/CT were prospectively recruited for PET/MRI performed immediately after the PET/CT. Images were evaluated for quality, lesion detection and anatomical localization of FDG uptake. Maximum and mean standardized uptake values (SUVmax/mean) of normal organs and SUVmax of the most FDG-avid lesions were measured for PET/MRI and PET/CT. Estimation of radiation exposure was calculated using specific age-related factors.

RESULTS

Nine PET/MRI scans were performed in eight patients (mean age: 15.3 years). The mean time interval between PET/CT and PET/MRI was 51 ± 10 min. Both the PET/CT and PET/MRI exams had good image quality and alignment with complete (9/9) concordance in response assessment. The SUVs from PET/MRI and PET/CT were highly correlated for normal organs (SUVmean r(2): 0.88, P<0.0001) and very highly for FDG-avid lesions (SUVmax r(2): 0.94, P=0.0002). PET/MRI demonstrated an average percent radiation exposure reduction of 39% ± 13% compared with PET/CT.

CONCLUSION

Simultaneous whole-body PET/MRI is clinically feasible in pediatric lymphoma. PET/MRI performance is comparable to PET/CT for lesion detection and SUV measurements. Replacement of PET/CT with PET/MRI can significantly decrease radiation dose from diagnostic imaging in children.

(18)F Sodium Fluoride PET/CT in Patients with Prostate Cancer: Quantification of Normal Tissues, Benign Degenerative Lesions, and Malignant Lesions

Understanding the range and variability of normal, benign degenerative, and malignant ¹⁸F sodium fluoride (¹⁸F NaF) positron emission tomography/computed tomography (PET/CT) uptake is important in influencing clinical interpretation. Further, it is essential for the development of realistic semiautomated quantification techniques and simulation models. The purpose of this study is to determine the range of these values in a clinically relevant patient population with prostate cancer. ¹⁸F NaF PET/CT scans were analyzed in patients with prostate cancer (n = 47) referred for evaluation of bone metastases. Mean and maximum standardized uptake values [SUVs (SUV_mean and SUV_max)] were made in normal background regions (n = 470) including soft tissues (liver, aorta, bladder, adipose, brain, and paraspinal muscle) and osseous structures (T12 vertebral body, femoral diaphyseal cortex, femoral head medullary space, and ribs). Degenerative joint disease (DJD; n = 281) and bone metastases (n = 159) were identified and quantified by an experienced reader using all scan information including coregistered CT. For normal bone regions, the highest ¹⁸F NaF PET SUV_mean occurred in T12 (6.8 ± 1.4) and it also showed the lowest coefficient of variation (cv = 21%). For normal soft tissues, paraspinal muscles showed very low SUV_mean (0.70 ± 0.11) and also showed the lowest variability (cv = 16%). Average SUV_mean in metastatic lesions is higher than uptake in benign degenerative lesions but values showed a wide variance and overlapping values (16.3 ± 13 vs 11.1 ± 3.8; P < 0.00001). The normal ¹⁸F NaF PET uptake values for prostate cancer patients in normal background, benign degenerative disease, and osseous metastases are comparable to those reported for a general population with a wide variety of diagnoses. These normal ranges, specifically for prostate cancer patients, will aid in clinical interpretation and also help to establish the basis of normal limits in a semiautomated data analysis algorithm.

Impacts of biological and procedural factors on semiquantification uptake value of liver in fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography imaging

BACKGROUND

Increased metabolic activity of fluorodeoxyglucose (FDG) in tissue is not only resulting of pathological uptake, but due to physiological uptake as well. This study aimed to determine the impacts of biological and procedural factors on FDG uptake of liver in whole body positron emission tomography/computed tomography (PET/CT) imaging.

METHODS

Whole body fluorine-18 ((18)F) FDG PET/CT scans of 51 oncology patients have been reviewed. Maximum standardized uptake value (SUVmax) of lesion-free liver was quantified in each patient. Pearson correlation was performed to determine the association between the factors of age, body mass index (BMI), blood glucose level, FDG dose and incubation period and liver SUVmax. Multivariate regression analysis was established to determine the significant factors that best predicted the liver SUVmax. Then the subjects were dichotomised into four BMI groups. Analysis of variance (ANOVA) was established for mean difference of SUVmax of liver between those BMI groups.

RESULTS

BMI and incubation period were significantly associated with liver SUVmax. These factors were accounted for 29.6% of the liver SUVmax variance. Statistically significant differences were observed in the mean SUVmax of liver among those BMI groups (P<0.05).

CONCLUSIONS

BMI and incubation period are significant factors affecting physiological FDG uptake of liver. It would be recommended to employ different cut-off value for physiological liver SUVmax as a reference standard for different BMI of patients in PET/CT interpretation and use a standard protocol for incubation period of patient to reduce variation in physiological FDG uptake of liver in PET/CT study.

Liver metabolic activity changes over time with neoadjuvant therapy in locally advanced rectal cancer

OBJECTIVE

The aim of this study was to evaluate, using PET/computed tomography (CT), changes in liver metabolic activity in patients with locally advanced rectal cancer (LARC) after neoadjuvant chemoradiotherapy (CRT).

PATIENTS AND METHODS

A total of 29 biopsy-proven LARC patients between 2009 and 2012 were studied. Liver standardized uptake values (SUVs) and SUVs adjusted for lean body mass (SULs) were obtained from PET/CT images obtained at 1 h (early) and 2 h (late) after (18)F-fluorodeoxyglucose ((18)F-FDG) administration both before and after neoadjuvant CRT. Age, sex, BMI, lean body mass, blood glucose level, and (18)F-FDG dose, which can influence liver SUVs and SULs, were also analyzed.

RESULTS

Fourteen (48%) men and 15 (52%) women with a mean age of 62±11 years (range 34-80 years) were included in the study. The mean SUVs and SULs were significantly decreased in the late scans. Sex was significantly correlated with the mean liver SUV in early and late scans. The mean SUV differed significantly between male and female patients in early and late images (P<0.05). In a multivariate stepwise regression analysis, only liver SUVs (maximum and mean) were significantly associated with BMI before and after therapy. SUVs were significantly higher in the high (≥25) BMI group after but not before therapy. Mean SUL was not influenced by BMI.

CONCLUSION

Liver (18)F-FDG uptake is consistent before and after neoadjuvant CRT therapy in patients with LARC. When assessing response to therapy and using liver metabolic activity to indicate background activity, BMI should be considered as it can influence liver metabolic activity.

Ratio of Lymph Node to Primary Tumor SUV on PET/CT Accurately Predicts Nodal Malignancy in Non-Small-Cell Lung Cancer

Thoracic lymph nodes with marginally elevated maximum standardized uptake value (SUVmax) on PET/CT a diagnostic challenge in staging non-small-cell lung cancer. We evaluated the ratio of lymph node to primary tumor SUVmax (SUVN/T) in predicting nodal malignancy among 132 sampled nodes from 85 patients both a primary tumor SUVmax > 2.5 and LN SUVmax 2.0 to 6.0. SUVN/T was more accurate than SUVmax for this subset of patients.

INTRODUCTION/BACKGROUND

Among non-small-cell lung cancers with appreciable functional activity, positron emission tomography/computed tomography (PET/CT) is the most accurate imaging modality for clinical staging. However, lymph nodes (LN) with marginally elevated standardized uptake value (SUV) present a diagnostic challenge. In this retrospective study, we hypothesized that normalizing the LN SUV by using the ratio of the LN to primary tumor SUVmax (SUVN/T) may be a better predictor of nodal malignancy than using SUVmax alone for nodes with low to intermediate SUV.

PATIENTS AND METHODS

We identified 172 patients with newly diagnosed non-small-cell lung cancer who underwent pathologic LN staging and PET/CT within 31 days before biopsy. Receiver operating characteristic curves with area under the curve (AUC) calculations were used to evaluate SUVmax and SUVN/T for their ability to predict nodal malignancy for both the entire cohort of 504 LNs and a subset of 132 LNs from 85 patients who had both primary tumor SUVmax > 2.5 and LN SUVmax 2.0 to 6.0.

RESULTS

In patients with primary tumor SUVmax > 2.5 and LN SUVmax 2.0 to 6.0, SUVN/T was significantly more accurate in predicting nodal malignancy (AUC, 0.846; 95% confidence interval, 0.775-0.917) than SUVmax (AUC, 0.653; 95% confidence interval, 0.548-0.759). The optimal cutoff value of SUVN/T to predict nodal malignancy was 0.28 (90% sensitivity, 68% specificity). Sensitivity was > 95% for SUVN/T < 0.21, whereas specificity was > 95% for SUVN/T > 0.50.

CONCLUSION

The ratio of LN SUV to primary tumor SUV on PET/CT is more accurate than SUVmax when assessing nodes of low to intermediate SUV.

Liver standardized uptake value corrected for lean body mass at FDG PET/CT: effect of FDG uptake time

OBJECTIVE

The objective of this study is to establish the magnitude change and interreader reliability of the liver standardized uptake value corrected for lean body mass (SULmean) in dual-time-point imaging at 1 and 2 hours and 1 and 4 hours.

PATIENTS AND METHODS

Early and delayed FDG PET/CT scans were included for 28 patients (13 men and 15 women) who had normal liver by CT or ultrasound. The average uptake time between the early and delayed scans were 55 minutes (range, 44-69 minutes) for pancreatic adenocarcinoma patients (n = 19) and 184 minutes (range, 140-197 minutes) for neurofibromatosis patients (n = 9). A 30-mm-diameter spherical volume of interest was placed within the right lobe of the liver above, below, and at the level of the main portal vein by 2 independent readers. Correlation coefficients, analysis of variance, intraclass correlation coefficient, and Bland-Altman analysis were performed.

RESULTS

The mean liver SULmean was between 1.39 and 1.42 and between 1.28 and 1.3 in early and delayed images, respectively (P = 0.001). There is time-dependent reduction in the mean liver SULmean at 2-hour (7%-8%) and 4-hour uptake time (15%-21%) compared with 1-hour uptake time. The correlation coefficient between delayed uptake time and liver SULmean reduction is 0.39 to 0.41 at the upper aspect of the liver. The intraclass correlation coefficient for 2 readers varied between 0.997 and 0.998 and between 0.995 and 0.999 in early and delayed images, respectively (P = 0.001).

CONCLUSIONS

There is time-dependent reduction of mean liver SULmean, about 7% to 8% within the clinically relevant FDG uptake time, in the same patient with excellent interreader agreement in early and delayed images within the right lobe of the liver. Therefore, liver SULmean could represent a useful reference parameter in quantitative analysis of dual-phase FDG PET/CT in malignancy or atypical infection/inflammatory disease. Furthermore, it may be suitable as a normalization factor in currently available formulae quantifying therapy response on PET imaging.

18F-FDG PET/CT oncologic imaging at extended injection-to-scan acquisition time intervals derived from a single-institution 18F-FDG-directed surgery experience: feasibility and quantification of 18F-FDG accumulation within 18F-FDG-avid lesions and background tissues

Background

¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) is a well-established imaging modality for a wide variety of solid malignancies. Currently, only limited data exists regarding the utility of PET/CT imaging at very extended injection-to-scan acquisition times. The current retrospective data analysis assessed the feasibility and quantification of diagnostic ¹⁸F-FDG PET/CT oncologic imaging at extended injection-to-scan acquisition time intervals.

Methods

¹⁸F-FDG-avid lesions (not surgically manipulated or altered during ¹⁸F-FDG-directed surgery, and visualized both on preoperative and postoperative ¹⁸F-FDG PET/CT imaging) and corresponding background tissues were assessed for ¹⁸F-FDG accumulation on same-day preoperative and postoperative ¹⁸F-FDG PET/CT imaging. Multiple patient variables and ¹⁸F-FDG-avid lesion variables were examined.

Results

For the 32 ¹⁸F-FDG-avid lesions making up the final ¹⁸F-FDG-avid lesion data set (from among 7 patients), the mean injection-to-scan times of the preoperative and postoperative ¹⁸F-FDG PET/CT scans were 73 (±3, 70-78) and 530 (±79, 413-739) minutes, respectively (P < 0.001). The preoperative and postoperative mean ¹⁸F-FDG-avid lesion SUV_max values were 7.7 (±4.0, 3.6-19.5) and 11.3 (±6.0, 4.1-29.2), respectively (P < 0.001). The preoperative and postoperative mean background SUV_max values were 2.3 (±0.6, 1.0-3.2) and 2.1 (±0.6, 1.0-3.3), respectively (P = 0.017). The preoperative and postoperative mean lesion-to-background SUV_max ratios were 3.7 (±2.3, 1.5-9.8) and 5.8 (±3.6, 1.6-16.2), respectively, (P < 0.001).

Conclusions

¹⁸F-FDG PET/CT oncologic imaging can be successfully performed at extended injection-to-scan acquisition time intervals of up to approximately 5 half-lives for ¹⁸F-FDG while maintaining good/adequate diagnostic image quality. The resultant increase in the ¹⁸F-FDG-avid lesion SUV_max values, decreased background SUV_max values, and increased lesion-to-background SUV_max ratios seen from preoperative to postoperative ¹⁸F-FDG PET/CT imaging have great potential for allowing for the integrated, real-time use of ¹⁸F-FDG PET/CT imaging in conjunction with ¹⁸F-FDG-directed interventional radiology biopsy and ablation procedures and ¹⁸F-FDG-directed surgical procedures, as well as have far-reaching impact on potentially re-shaping future thinking regarding the “most optimal” injection-to-scan acquisition time interval for all routine diagnostic ¹⁸F-FDG PET/CT oncologic imaging.

Comparison of standardized uptake values in normal structures between PET/CT and PET/MRI in an oncology patient population

PURPOSE

The purpose of this study was to compare and correlate standardized uptake values (SUV) derived from magnetic resonance attenuation correction (MRAC) with those derived from computed tomography attenuation correction (CTAC) in an oncology patient population.

PROCEDURES

The HIPAA-compliant study was approved by the Internal Review Board and all subjects gave written informed consent prior to inclusion in the study. Forty patients (mean age 61 ± 15.1; 20 male) referred for clinically indicated 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) positron emission tomography/computed tomography (PET/CT) scans also underwent a PET/magnetic resonance imaging (MRI) examination. MRAC was performed using an automatic three-segment model. Regions of interest were drawn over eight normal structures in order to obtain SUVmax and SUVmean values. Spearman rank correlation coefficients (r) were calculated and two-tailed paired t tests were performed to compare the SUVmax and SUVmean values obtained from CTAC with those from MRAC.

RESULTS

The mean time after FDG injection was 66 ± 7 min for PET/CT and 117 ± 15 min for PET/MRI examination. MRAC SUV values were significantly lower than the CTAC SUV values in mediastinal blood pool (p < 0.001 for both SUVmax and SUVmean) and liver (p = 0.01 for SUVmean). The MRAC SUV values were significantly higher in bone marrow (p < 0.001 for both SUVmax and SUVmean), psoas major muscle (p < 0.001 for SUVmax), and left ventricular myocardium (p < 0.001 for SUVmax and p = 0.01 for SUVmean). For the other normal structures, no significant difference was observed. When comparing SUV values generated from CTAC versus MRAC, high correlations between CTAC and MRAC were observed in myocardium (r = 0.96/0.97 for SUVmax/mean), liver (r = 0.68 for SUVmax), bone marrow (r = 0.80/0.83 for SUVmax/mean), lung tissue (r = 0.70 for SUVmax), and mediastinal blood pool (r = 0.0.68/.069 for SUVmax/mean). Moderate correlations were found in lung tissue (r = 0.67 for SUV mean), liver (r = 0.66 for SUVmean), fat (r = 0.48/0.53 for SUVmax/mean), psoas major muscle (r = 0.54/0.58 for SUVmax/mean), and iliacus muscle (r = 0.41 for SUVmax). Low correlation was found in iliacus muscle (r = 0.32 for SUVmean).

CONCLUSIONS

Using the automatic three-segment model, our study showed high correlation for measurement of SUV values obtained from MRAC compared to those from CTAC, as the reference standard. Differences observed between MRAC and CTAC derived SUV values may be attributed to the time-delay between the PET/CT and PET/MRI scans or biologic clearance of radiotracer. Further studies are required to assess SUV measurements when performing different MR attenuation correction techniques.

Factors affecting intrapatient liver and mediastinal blood pool ¹⁸F-FDG standardized uptake value changes during ABVD chemotherapy in Hodgkin's lymphoma

PURPOSE

The aim of our study was to assess the intrapatient variability of 2-deoxy-2-((18)F)-fluoro-D-glucose ((18)F-FDG) uptake in the liver and in the mediastinum among patients with Hodgkin's lymphoma (HL) treated with doxorubicin (Adriamycin), bleomycin, vinblastine and dacarbazine (ABVD) chemotherapy (CHT).

METHODS

The study included 68 patients (30 men, 38 women; mean age 32 ± 11 years) with biopsy-proven HL. According to Ann Arbor criteria, 6 were stage I, 34 were stage II, 12 were stage 3 and 16 were stage 4. All of them underwent a baseline (PET0) and an interim (PET2) (18)F-FDG whole-body positron emission tomography (PET)/CT. All patients were treated after PET0 with two ABVD cycles for 2 months that ended 15 ± 5 days prior to the PET2 examination. All patients were further evaluated 15 ± 6 days after four additional ABVD cycles (PET6). None of the patients presented a serum glucose level higher than 107 mg/dl. The mean and maximum standardized uptake values (SUV) of the liver and mediastinum were calculated using the same standard protocol for PET0, PET2 and PET6, respectively. Data were examined by means of the Wilcoxon matched pairs test and linear regression analysis.

RESULTS

The main results of our study were an increased liver SUVmean in PET2 (1.76 ± 0.35) as compared with that of PET0 (1.57 ± 0.31; p < 0.0001) and PET6 (1.69 ± 0.28; p = 0.0407). The same results were obtained when considering liver SUVmax in PET2 (3.13 ± 0.67) as compared with that of PET0 (2.82 ± 0.64; p < 0.0001) and PET6 (2.96 ± 0.52; p = 0.0105). No significant differences were obtained when comparing mediastinum SUVmean and SUVmax in PET0, PET2 and PET6 (p > 0.05). Another finding is a relationship in PET0 between liver SUVmean and SUVmax with the stage, which was lower in those patients with advanced disease (r (2) = 0.1456 and p = 0.0013 for SUVmean and r (2) = 0.1277 and p = 0.0028 for SUVmax).

CONCLUSION

The results of our study suggest that liver (18)F-FDG uptake is variable in patients with HL during the CHT treatment and the disease course and should be considered carefully when used to define the response to therapy in the interim PET in HL.

Aortic 18F-FDG PET/CT uptake pattern at 60 min (early) and 180 min (delayed) acquisition in a control population: a visual and semiquantitative comparative analysis

18F-Fluoro-2-deoxy-D-glucose (F-FDG) PET/CT acquisition is generally performed 60 min after injection. The normal biodistribution pattern of F-FDG includes activity in the aortic territory due to blood pool activity, which could interfere in the diagnosis of aortic diseases by overlapping the wall uptake. The aim of the study was to evaluate the change over time of F-FDG uptake by the aortic wall and the activity in the lumen in a control population and to establish normal reference values. This prospective study included 15 control patients (mean age: 58.2 years). PET/CT was acquired 60 min (early scan) and 180 min (delayed scan) after an F-FDG injection at a dose of 7 MBq/kg. A visual and semiquantitative analysis of the F-FDG aortic wall uptake was carried out, and lumen activity and the aortic wall to lumen ratio [target-to-background ratio (TBR)] were determined. In the visual analysis all patients showed F-FDG activity at the aortic territory at 60 and 180 min. The pattern of uptake at 60 min was diffuse in all 15 patients (100%), without delineation of the aortic wall uptake; however, at 180 min the uptake pattern of the aortic wall changed to lineal in 14 patients (93.3%). The aortic wall maximum standardized uptake value decreased from 2.07±0.34 to 1.7±0.46 during the delayed acquisition (P=0.0279) and the lumen maximum standardized uptake value decreased highly significantly (1.99±0.35 vs. 1.36±0.32, P=0.0001). Therefore, TBR also increased highly significantly from 1.04±0.06 to 1.25±0.16 (P<0.0001). The high decrease in blood pool activity from 60 to 180 min provides a better delineation of the aortic wall uptake, which corresponds to the normal pattern at that time. The TBR increased significantly at 180 min, and 1.25±0.16 is suggested as the threshold for diagnostic purposes, especially for the diagnosis of vasculitis.

When should we recommend use of dual time-point and delayed time-point imaging techniques in FDG PET?

FDG PET and PET/CT are now widely used in oncological imaging for tumor characterization, staging, restaging, and response evaluation. However, numerous benign etiologies may cause increased FDG uptake indistinguishable from that of malignancy. Multiple studies have shown that dual time-point imaging (DTPI) of FDG PET may be helpful in differentiating malignancy from benign processes. However, exceptions exist, and some studies have demonstrated significant overlap of FDG uptake patterns between benign and malignant lesions on delayed time-point images. In this review, we summarize our experience and opinions on the value of DTPI and delayed time-point imaging in oncology, with a review of the relevant literature. We believe that the major value of DTPI and delayed time-point imaging is the increased sensitivity due to continued clearance of background activity and continued FDG accumulation in malignant lesions, if the same diagnostic criteria (as in the initial standard single time-point imaging) are used. The specificity of DTPI and delayed time-point imaging depends on multiple factors, including the prevalence of malignancies, the patient population, and the cut-off values (either SUV or retention index) used to define a malignancy. Thus, DTPI and delayed time-point imaging would be more useful if performed for evaluation of lesions in regions with significant background activity clearance over time (such as the liver, the spleen, the mediastinum), and if used in the evaluation of the extent of tumor involvement rather than in the characterization of the nature of any specific lesion. Acute infectious and non-infectious inflammatory lesions remain as the major culprit for diminished diagnostic performance of these approaches (especially in tuberculosis-endemic regions). Tumor heterogeneity may also contribute to inconsistent performance of DTPI. The authors believe that selective use of DTPI and delayed time-point imaging will improve diagnostic accuracy and interpretation confidence in FDG PET imaging.

A multicenter prospective evaluation of the clinical utility of F-18 FDG-PET/CT in patients with AJCC stage IIIB or IIIC extremity melanoma

OBJECTIVE/BACKGROUND

There is a high risk of relapse in stage IIIB/IIIC melanoma. The utility of 2-[fluorine-18]-fluoro-2-deoxy-D-glucose positron emission tomography integrated with computed tomography (FDG-PET/CT) in these patients to evaluate response to treatment or for surveillance after treatment is currently not well defined.

METHODS

Prospective data from 2 centers identified 97 patients with stage IIIB/IIIC extremity melanoma undergoing isolated limb infusion (ILI) who had whole body FDG-PET/CT scans before and every 3 months after treatment. Clinical response was determined at 3 months by Response Evaluation Criteria In Solid Tumors.

RESULTS

Complete response (CR) after ILI occurred in 33% (32/97) of patients. FDG-PET/CT accurately identified 59% of patients who were CRs (19/32), whereas 41% (13/32) had residual metabolic activity in the extremity that was histologically negative for melanoma. The 3-year disease-free rate was 62.2% (95% CI: 40.1%-96.4%) for those patients who were CRs by both clinical/pathologic examination and FDG-PET/CT (n = 19) compared to only 29.4% (95% CI: 9.9%-87.2%) of those CRs who still had residual FDG-PET/CT activity (n = 13). FDG-PET/CT was utilized for surveillance of disease recurrence outside the regional field of treatment. Fifty-two percent (51/97) of patients developed disease outside the extremity at a median time of 212 days from pre-ILI FDG-PET/CT. In 47% (29/62) of these cases, the recurrence was resected.

CONCLUSIONS

Although FDG-PET/CT does not appear to accurately identify patients who appear to be CRs to ILI, it does appear to identify a subgroup of patients whose regional progression-free survival is markedly worse. However, FDG-PET/CT appears to be an excellent method for surveillance in stage IIIB/IIIC patients after ILI with ability to identify surgically resectable recurrent disease in these high-risk patients.

Estimating the whole bone-marrow asset in humans by a computational approach to integrated PET/CT imaging

PURPOSE

Despite their relevance in clinical medicine, the extension and activity of the bone marrow (BM) cannot be directly evaluated in vivo. We propose a new method to estimate these variables by combining structural and functional maps provided by CT and PET.

METHODS

BM extension and glucose uptake were estimated in 102 patients undergoing whole-body PET/CT because of a history of nonmetastatic melanoma. Image analysis assumed that the BM is surrounded by compact bone. An iterative optimization scheme was applied to each CT slice to identify the external border of the bone. To identify compact bone, the algorithm measured the average Hounsfield coefficient within a two-pixel ring located just inside the bone contour. All intraosseous pixels with an attenuation coefficient lower than this cut-off were flagged as 1, while the remaining pixels were set at 0. Binary masks created from all CT slices were thus applied to the PET data to determine the metabolic activity of the intraosseous volume (IBV).

RESULTS

Estimated whole-body IBV was 1,632 ± 587 cm(3) and was higher in men than in women (2,004 ± 498 cm(3) vs. 1,203 ± 354 cm(3), P < 0.001). Overall, it was strictly correlated with ideal body weight (r = 0.81, P = 0.001) but only loosely with measured body weight (r = 0.43, P = 0.01). The average FDG standardized uptake value (SUV) in the thoracic and lumbar vertebrae was 2.01 ± 0.36, Accordingly, intraosseous voxels with SUV ≥ 1.11 (mean spine SUV - 2.5 × SD) were considered as active "red" BM and those with SUV <1.11 as "yellow" BM. Estimated red BM volume was 541 ± 195 ml, with a higher prevalence in the axial than in the appendicular skeleton (87 ± 8 % vs. 10 ± 8 %, P < 0.001). Again, red BM volume was higher in men than in women (7.8 ± 2.2 vs. 6.7 ± 2.1 ml/kg body weight, P < 0.05), but in women it occupied a greater fraction of the IBV (32 ± 7 % vs. 36 ± 10 %, P < 0.05). Patient age modestly predicted red BM SUV, while it was robustly and inversely correlated with red BM volume.

CONCLUSION

Our computational analysis of PET/CT images provides a first estimation of the extension and metabolism of the BM in a population of adult patients without haematooncological disorders. This information might represent a new window to explore pathophysiology the BM and the response of BM diseases to chemotherapy.

When to image carotid plaque inflammation with FDG PET/CT

OBJECTIVE

Quantification of 18-fluorodeoxyglucose (FDG) uptake in inflamed high-risk carotid atherosclerotic plaques is challenged by the spatial resolution of positron emission tomography (PET) and luminal blood activity. Late acquisition protocols have been used to overcome these challenges to enhance the contrast between the plaque and blood-pool FDG activity. However, for prospective studies the late acquisition is inconvenient for the patient and staff, and most retrospective studies of plaque uptake use data from early acquisition protocols. The objective was to evaluate changes in the quantification methods of FDG uptake in carotid artery plaques between early and late PET scans.

METHODS

FDG uptake 1 and 3 h after tracer injection was compared in 19 carotid artery plaques. The average plaque maximum standardized uptake value (SUVmax) and a target to background ratio (TBR), using venous blood-pool activity as background, were evaluated at the two time points. These methods have been shown earlier to quantitate the degree of inflammation in late hour scans.

RESULTS

A good individual plaque FDG uptake consistency was found between the two time points for SUVmax, r²=0.86. In contrast, the ratio method did not conserve the results between the two time points: TBR r²=0.34. For both methods, absolute values changed over time. TBR values generally increased as blood pool activity decreased, whereas the individual plaque SUVmax values showed both increases and decreases over time.

CONCLUSION

Identification of carotid plaque inflammation with PET can be performed 1 h after FDG injection using SUVmax for plaque FDG uptake quantification.

Effects of blood glucose level on FDG uptake by liver: a FDG-PET/CT study

In FDG-PET for abdominal malignancy, the liver may be assumed as an internal standard for grading abnormal FDG uptake both in early images and in delayed images. However, physiological variables of FDG uptake by the liver, especially the effects of blood glucose level, have not yet been elucidated.

METHODS

FDG-PET studies of 70 patients examined at 50 to 70 min after injection (60 ± 10 min: early images) and of 68 patients examined at 80 to 100 min after injection (90 ± 10 min: delayed images) were analyzed for liver FDG uptake. Patients having lesions in the liver, spleen and pancreas; patients having bulk tumor in other areas; and patients early after chemotherapy or radiotherapy were excluded; also, patients with blood glucose level over 125 mg/dl were excluded.

RESULTS

Mean standardized uptake value (SUV) of the liver, blood glucose level and sex showed no significant differences between early images and delayed images. However, liver SUV in the delayed image showed a larger variation than that in the early image and showed significant correlation to blood glucose level. The partial correlation coefficient between liver SUV and blood glucose level in the delayed image with adjustment for sex and age was 0.73 (P < .0001). Multivariate regression coefficient (95% confidence interval) of blood glucose was 0.017 (0.013-0.021).

CONCLUSION

Blood glucose level is an important factor affecting the normal liver FDG uptake in nondiabetic patients. In the case of higher glucose level, liver FDG uptake is elevated especially in the delayed image. This may be due to the fact that the liver is the key organ responsible for glucose metabolism through gluconeogenesis and glycogen storage.

Physiology and pathophysiology of incidental findings detected on FDG-PET scintigraphy

A routine feature of positron emission tomography/computed tomography (PET/CT) imaging is whole-body acquisition that results in many unexpected findings identified outside of the primary region of abnormality. Furthermore, (18)F-fluorodeoxyglucose (FDG) is a marker of glycolysis and does not specifically accumulate in malignancy. Understanding the physiology and pathophysiology of normal FDG distribution and common incidental findings is therefore essential to the physician interpreting whole-body FDG-PET/CT studies. Whereas many incidental findings are benign and of limited clinical significance, others represent uncommon manifestations of the primary malignancy, second malignancies, or various clinically significant pathologic processes. Patients with a single malignancy are at greater risk of developing synchronous or metachronous second malignancies, possibly related to exposure to shared carcinogenic agents or presence of prooncogenic mutations. The decision of how to pursue an intervention on the basis of an incidental finding is generally left to clinical judgment.

A systematic review of the factors affecting accuracy of SUV measurements

OBJECTIVE

There is growing interest in using PET/CT for evaluating early response to therapy in cancer treatment. Although widely available and convenient to use, standardized uptake value (SUV) measurements can be influenced by a variety of biologic and technologic factors. Many of these factors can be addressed with close attention to detail and appropriate quality control. This article will review factors potentially affecting SUV measurements and provide recommendations on ways to minimize when using serial PET to assess early response to therapy.

CONCLUSION

Scanner and reconstruction parameters can significantly affect SUV measurements. When using serial SUV measurements to assess early response to therapy, imaging should be performed on the same scanner using the same image acquisition and reconstruction protocols. In addition, attention to detail is required for accurate determination of the administered radiopharmaceutical dose.

(18)F-FDG PET-CT respiratory gating in characterization of pulmonary lesions: approximation towards clinical indications

AIM

To evaluate the effect of the 18F-FDG PET-CT respiratory gating (4D) study in the correct documentation of pulmonary lesions with faint uptake in standard PET-CT.

METHODS

Forty-two pulmonary lesions with a low or no detectable uptake of FDG (SUV(max) < 2.5) in 3D PET-CT were prospectively evaluated in 28 patients (19 males and 9 females), mean age 66.5 years (41-81). 22 patients had neoplastic background. A conventional PET-CT (3D) total body scan was performed approximately 60 min after iv injection of a mean dose of 370 MBq. Furthermore, a 4D PET-CT (synchronized with respiratory movement) thorax study was acquired. SUV(max) was determined for each lesion in both studies. For the 4D studies, we selected the SUV(max) in respiratory period with the highest uptake ("best bin"). We calculated the SUV(max) percentage difference between 3D and 4D PET-CT (% difference = SUV(max) 4D - SUV(max) 3D/SUV(max) 3D x 100) and the relation of this value with the size and locations of the lesions. In 4D study, any lesion with SUV(max) > or = 2.5 was classified as malignant. We assessed the changes of lesion classification (from benign to malignant) applying the 4D technique. The final diagnosis was obtained by histological assessment or clinical and radiological follow-up longer than 12 months.

RESULTS

Forty out of 42 lesions showed an increase of SUV(max) in the 4D study with respect to 3D. The mean SUV(max) in the 3D and 4D PET-CT studies were 1.33 (+/-0.59) and 2.26 (+/-0.87), respectively. The SUV(max) percentage difference mean between both techniques was 83.3% (+/-80.81).The smaller the lesion the greater was the SUV(max) percentage difference (P < 0.05). No differences were observed depending on the location of the lesion. In 40% of cases, there was a change in the final classification of lesions from benign to malignant. In the final diagnosis, 24 lesions were malignant. 4D PET-CT diagnosed correctly the 52% of them.

CONCLUSIONS

The 4D PET-CT study permitted a better characterization of malignant lung lesions compared with the standard PET-CT, because of its higher sensitivity. 4D PET-CT is a recommendable technique in the early diagnosis of malignant lesions.