Positron emission tomography/computed tomography: the current technology and applications

Enhanced Diagnostic Precision: Assessing Tumor Differentiation in Head and Neck Squamous Cell Carcinoma Using Multi-Slice Spiral CT Texture Analysis

This study explores the efficacy of texture analysis by using preoperative multi-slice spiral computed tomography (MSCT) to non-invasively determine the grade of cellular differentiation in head and neck squamous cell carcinoma (HNSCC). In a retrospective study, MSCT scans of patients with HNSCC were analyzed and classified based on its histological grade as moderately differentiated, well-differentiated, or poorly differentiated. The location of the tumor was categorized as either in the bone or in soft tissues. Segmentation of the lesion areas was conducted, followed by texture analysis. Eleven GLCM parameters across five different distances were calculated. Median values and correlations of texture parameters were examined in relation to tumor differentiation grade by using Spearman's correlation coefficient and Kruskal-Wallis and Dunn tests. Forty-six patients were included, predominantly female (87%), with a mean age of 66.7 years. Texture analysis revealed significant parameter correlations with histopathological grades of tumor differentiation. The study identified no significant age correlation with tumor differentiation, which underscores the potential of texture analysis as an age-independent biomarker. The strong correlations between texture parameters and histopathological grades support the integration of this technique into the clinical decision-making process.

Digital PET vs Analog PET: Clinical Implications?

Positron emission tomography (PET) is a functional imaging technique introduced in 1970s. Over the years, PET was used alone but is in 2000 when the first hybrid PET/CT device was clinically introduced. Since then, PET has continuously been marked by technological developments, being the most recent one the introduction of silicon photomultipliers (SiPMs) as an alternative to standard photomultiplier tubes used in analog PET/CT systems. SiPMs, the basis for the so called digital PET/CT systems, are smaller than standard photomultiplier tubes (enabling higher spatial resolution) and provide up to 100% coverage of the crystal area, as well as high sensitivity, low noise, and fast timing resolution. SiPMs in combination with optimized acquisition and reconstruction parameters improve the localization of the annihilation events, provide high definition PET images, and offer higher sensitivity and higher diagnostic performance. This article summarizes the evidence about the superior performance of the state of the art digital PET and highlights its potential clinical implications. Digital PET opens new perspectives in the quantification and characterization of small lesions, which are mostly undetectable using analog PET systems, potentially changing patient management and improving outcomes in oncological and non-oncological diseases. Moreover, digital PET offers the possibility to reduce radiation dose and scan times which may facilitate the implementation of PET to address unmet clinical needs.

Oncologic Imaging of the Lymphatic System: Current Perspective with Multi-Modality Imaging and New Horizon

The lymphatic system is an anatomically complex vascular network that is responsible for interstitial fluid homeostasis, transport of large interstitial particles and cells, immunity, and lipid absorption in the gastrointestinal tract. This network of specially adapted vessels and lymphoid tissue provides a major pathway for metastatic spread. Many malignancies produce vascular endothelial factors that induce tumoral and peritumoral lymphangiogenesis, increasing the likelihood for lymphatic spread. Radiologic evaluation for disease staging is the cornerstone of oncologic patient treatment and management. Multiple imaging modalities are available to access both local and distant metastasis. In this manuscript, we review the anatomy, physiology, and imaging of the lymphatic system.

Diagnostic accuracy of 18F-FDG-PET in abdominal sepsis in rats

Purpose

The objective of this study was to investigate the accuracy of 18F-FDG-PET in the diagnosis of multibacterial abdominal sepsis by cecum ligation and puncture (CLP) in rats.

Methods

Adult Wistar rats ( Rattus norvegicus ), weighing 227±35g, were allocated into a sepsis group by CLP (n=10) and sham group (n=10). 18F-FDG-PET using microPET was performed on all rats after 24 hours.

Results

All animals survived for postoperative 24h. The abdomen/liver ratio of the standardized uptake value (SUV) percentage was significantly higher in the sepsis group than in the sham (p=0.004). The ROC curve showed an accuracy of 18F-FDG-PET to detect abdominal sepsis of 88.9% (p=0.001), sensitivity of 90% and specificity of 88.9%. When a cut-off point of 79% of the ratio between the SUV on the abdominal region and liver was established, the sensitivity was 90%, specificity of 88.9%; positive and negative predictive values of 90.0% and 88.9%, respectively.

Conclusions

The diagnostic accuracy of 18F-FDG-PET in rats with abdominal sepsis was significantly high. It was also demonstrated the predictive ability of the abdomen/liver SUV ratio to diagnose abdominal sepsis. These findings may have implications for the clinical setting, locating septic foci with PETscan.

Synthesis and pre-clinical evaluation of a new class of high-affinity 18F-labeled PSMA ligands for detection of prostate cancer by PET imaging

Purpose

Current clinical imaging of PSMA-positive prostate cancer by positron emission tomography (PET) mainly features ⁶⁸Ga-labeled tracers, notably [⁶⁸Ga]Ga-PSMA-HBED-CC. The longer half-life of fluorine-18 offers significant advantages over Ga-68, clinically and logistically. We aimed to develop high-affinity PSMA inhibitors labeled with fluorine-18 as alternative tracers for prostate cancer.

Methods

Six triazolylphenyl ureas and their alkyne precursors were synthesized from the Glu-urea-Lys PSMA binding moiety. PSMA affinity was determined in a competitive binding assay using LNCaP cells. The [¹⁸F]triazoles were isolated following a Cu(I)-catalyzed click reaction between the alkynes and [¹⁸F]fluoroethylazide. The ¹⁸F-labeled compounds were evaluated in nude mice bearing LNCaP tumors and compared to [⁶⁸Ga]Ga-PSMA-HBED-CC and [¹⁸F]DCFPyL. Biodistribution studies of the two tracers with the highest imaged-derived tumor uptake and highest PSMA affinity were undertaken at 1 h, 2 h and 4 h post-injection (p.i.), and co-administration of PMPA was used to determine whether uptake was PSMA-specific.

Results

F-18-labeled triazolylphenyl ureas were prepared with a decay-corrected RCY of 20–40 %, >98 % radiochemical and chemical purity, and specific activity of up to 391 GBq/μmol. PSMA binding (IC₅₀) ranged from 3–36 nM. The position of the triazole influenced tumor uptake (3 > 4 > 2), and direct conjugation of the triazole with the phenylurea moiety was preferred to insertion of a spacer group. Image-derived tumor uptake ranged from 6–14 %ID/g at 2 h p.i., the time of maximum tumor uptake; uptake of [⁶⁸Ga]Ga-PSMA-HBED-CC and [¹⁸F]DCFPyL was 5–6 %ID/g at 1–3 h p.i., the time of maximum tumor uptake. Biodistribution studies of the two most promising compounds gave maximum tumor uptakes of 10.9 ± 1.0 % and 14.3 ± 2.5 %ID/g, respectively, as compared to 6.27 ± 1.44 %ID/g for [⁶⁸Ga]Ga-PSMA-HBED-CC.

Conclusions

Six [¹⁸F]triazolylphenyl ureas were prepared in good radiochemical yield. Compounds showed PSMA-specific uptake in LNCaP tumors as high as 14 % ID/g, more than a 2-fold increase over [⁶⁸Ga]Ga-PSMA-HBED-CC. The facile and high-yielding radiosynthesis of these ¹⁸F-labeled triazoles as well as their promising in vitro and in vivo characteristics make them worthy of clinical development for PET imaging of prostate cancer.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-016-3556-5) contains supplementary material, which is available to authorized users.

Imaging quality of (44)Sc in comparison with five other PET radionuclides using Derenzo phantoms and preclinical PET

PET is the favored nuclear imaging technique because of the high sensitivity and resolution it provides, as well as the possibility for quantification of accumulated radioactivity. (44)Sc (T1/2=3.97h, Eβ(+)=632keV) was recently proposed as a potentially interesting radionuclide for PET. The aim of this study was to investigate the image quality, which can be obtained with (44)Sc, and compare it with five other, frequently employed PET nuclides using Derenzo phantoms and a small-animal PET scanner. The radionuclides were produced at the medical cyclotron at CRS, ETH Zurich ((11)C, (18)F), at the Injector II research cyclotron at CRS, PSI ((64)Cu, (89)Zr, (44)Sc), as well as via a generator system ((68)Ga). Derenzo phantoms, containing solutions of each of these radionuclides, were scanned using a GE Healthcare eXplore VISTA small-animal PET scanner. The image resolution was determined for each nuclide by analysis of the intensity signal using the reconstructed PET data of a hole diameter of 1.3mm. The image quality of (44)Sc was compared to five frequently-used PET radionuclides. In agreement with the positron range, an increasing relative resolution was determined in the sequence of (68)Ga<(44)Sc<(89)Zr<(11)C<(64)Cu<(18)F. The performance of (44)Sc was in agreement with the theoretical expectations based on the energy of the emitted positrons.

Digital Microfluidics: A New Paradigm for Radiochemistry

The emerging technology of digital microfluidics is opening up the possibility of performing radiochemistry at the microliter scale to produce tracers for positron emission tomography (PET) labeled with fluorine-18 or other isotopes. Working at this volume scale not only reduces reagent costs but also improves specific activity (SA) by reducing contamination by the stable isotope. This technology could provide a practical means to routinely prepare high-SA tracers for applications such as neuroimaging and could make it possible to routinely achieve high SA using synthesis strategies such as isotopic exchange. Reagent droplets are controlled electronically, providing high reliability, a compact control system, and flexibility for diverse syntheses with a single-chip design. The compact size may enable the development of a self-shielded synthesizer that does not require a hot cell. This article reviews the progress of this technology and its application to the synthesis of PET tracers.

Intravenous contrast-enhanced CT can be used for CT-based attenuation correction in clinical (111)In-octreotide SPECT/CT

BACKGROUND

CT-based attenuation correction (CT-AC) using contrast-enhancement CT impacts (111)In-SPECT image quality and quantification. In this study we assessed and evaluated the effect.

METHODS

A phantom (5.15 L) was filled with an aqueous solution of In-111. Three SPECT/CT scans were performed: (A) no IV contrast, (B) with 100-mL IV contrast, and (C) with 200-mL IV contrast added. Scan protocol included a localization CT, a low-dose CT (LD), and a full-dose CT (FD). Phantom, LD and FD scan series were performed at 90, 120, and 140 kVp. Phantom data were evaluated looking at mean counts in a central volume. Ten patients referred for (111)In-octreotide scintigraphy were scanned according to our clinical (111)In-SPECT/CT protocol including a topogram, a LD (140 kVp), and a FD (120 kVp). The FD/contrast-enhanced CT was acquired in both arterial (FDAP) and venous phase (FDVP) following a mono-phasic IV injection of 125-mL Optiray (4.5 mL/s). For patient data, we report image quality, Krenning scores, and mean/max values for liver and tumor regions.

RESULTS

Phantoms: in uncorrected emission data, mean counts (average ± SD) decreased with increasing IV concentration: (A) 119 ± 9, (B) 113 ± 8, and (C) 110 ± 9. For all attenuation correction (AC) scans, the mean values increased with increasing iodine concentration.

PATIENTS

there were no visible artifacts in single photon emission computed tomography (SPECT) following CT-AC with contrast-enhanced CT. The average score of image quality was 4.1 ± 0.3, 3.8 ± 0.4, and 4.2 ± 0.4 for LD, arterial phase, and venous phase, respectively. A total of 16 lesions were detected. The Krenning scores of 13/16 lesions were identical across all scan series. The max pixel values for the 16 lesions showed generally lower values for LD than for contrast-enhanced CT.

CONCLUSIONS

In (111)In-SPECT/CT imaging of phantoms and patients, the use of IV CT contrast did neither degrade the SPECT image quality nor affect the clinical Krenning score. Reconstructed counts in healthy liver tissues were unaffected, and there was a generally lower count value in lesions following CT-AC based on the LD non-enhanced images. Overall, for clinical interpretation, no separate low-dose CT is required for CT-AC in (111)In-SPECT/CT.

A novel role of exogenous carbon monoxide on protecting cardiac function and improving survival against sepsis via mitochondrial energetic metabolism pathway

Septic cardiac dysfunction is the main cause of death in septic patients. Here we investigate whether exogenous carbon monoxide can protect cardiac function and improve survival against sepsis by interfering with mitochondrial energetic metabolism. Male C57BL/6 mice were subjected to cecal ligation and puncture to induce sepsis. Exogenous carbon monoxide delivered from Tricarbonyldichlororuthenium (II) dimer (carbon monoxide releasing molecule II, 8mg/kg) was used intravenously as intervention. We found that carbon monoxide significantly improved cardiac function (LVEF 80.26 ± 2.37% vs. 71.21 ± 1.37%, P < 0.001; LVFS 43.52 ± 1.92% vs. 34.93 ± 1.28%, P < 0.001) and increased survival rate of septic mice (63% vs. 25%, P < 0.01). This phenomenon might be owing to the beneficial effect of carbon monoxide on abolishing the elevation of cardiac enzyme activity, cytokines levels and apoptosis rate, then attenuating cardiac injury in septic mice. Meanwhile, carbon monoxide significantly reversed the loss of mitochondrial number, effectively inhibited cardiac mitochondrial damage in septic mice by modulating glucose uptake, adenosine triphosphate and lactate content. Furthermore upregulation of peroxisome proliferator-activated receptor-γ coactivator-1α, nuclear respiratory factor 1 and mitochondrial transcription factor A genes in cardiac tissue were revealed in septic mice treated with carbon monoxide. Taken together, the results indicate that exogenous carbon monoxide effectively modulated mitochondrial energetic metabolisms by interfering with expression of peroxisome proliferator-activated receptor-γ coactivator-1α, nuclear respiratory factor 1 and mitochondrial transcription factor A genes, consequently exerted an important improvement in sepsis-induced cardiac dysfunction.

Imaging biomarkers or biomarker imaging?

Since biomarker imaging is traditionally understood as imaging of molecular probes, we highly recommend to avoid any confusion with the previously defined term "imaging biomarkers" and, therefore, only use "molecular probe imaging (MPI)" in that context. Molecular probes (MPs) comprise all kinds of molecules administered to an organism which inherently carry a signalling moiety. This review highlights the basic concepts and differences of molecular probe imaging using specific biomarkers. In particular, PET radiopharmaceuticals are discussed in more detail. Specific radiochemical and radiopharmacological aspects as well as some legal issues are presented.

Distinguishing imaging features between spinal hyperplastic hematopoietic bone marrow and bone metastasis

BACKGROUND AND PURPOSE

Systematic investigations of the distinguishing imaging features between spinal hyperplastic hematopoietic bone marrow and bone metastasis have not been reported, to our knowledge. The purpose of this study was to determine the distinguishing imaging features of the 2 entities.

MATERIALS AND METHODS

We retrospectively reviewed the radiologic images of 8 consecutive male patients (age range, 52-78 years; mean, 64 years) with suspected spinal metastasis on MR imaging and FDG-PET, which was later confirmed as hyperplastic hematopoietic bone marrow. MR imaging, FDG-PET, CT, and bone scintigraphy images were qualitatively and/or quantitatively evaluated. Imaging findings in 24 patients with spinal metastasis were compared, and differences were statistically analyzed.

RESULTS

All 8 vertebral hyperplastic hematopoietic bone marrow lesions were hypointense on T1- and T2-weighted images; lesions contiguous with the adjacent vertebra were significantly more often seen in hyperplastic hematopoietic bone marrow than in metastasis (P = .035). T2 signal intensity of the lesion was significantly different between the 2 entities (P = .033). FDG-PET showed slightly higher uptake in all hyperplastic hematopoietic bone marrow lesions; their maximum standard uptake value was significantly lower than that of metastatic lesions (P = .037). CT attenuation of hyperplastic hematopoietic bone marrow was equal to or slightly higher than that of adjacent normal-appearing vertebra; the CT appearances of hyperplastic hematopoietic bone marrow and metastasis were significantly different (P < .01). Bone scintigraphy showed normal uptake for all vertebrae with hyperplastic hematopoietic bone marrow; the uptake was significantly different from that of metastasis (P < .01).

CONCLUSIONS

If a lesion was isointense to hyperintense to normal-appearing marrow on MR imaging or had a maximum standard uptake value of >3.6, the lesion was considered metastatic. A normal appearance on CT or bone scintigraphy excluded metastasis.

Regulatory effect and mechanisms of carbon monoxide-releasing molecule II on hepatic energy metabolism in septic mice

AIM: To investigate the possible mechanisms of exogenous carbon monoxide-releasing molecule II (CORM-2) intervention on hepatic energy metabolism in experimental sepsis.

METHODS: Forty-eight C57BL/6 mice were randomly divided into four groups (n = 12): sham group; cecal ligation and puncture (CLP) group; CLP + CORM-2 group and CLP + iCORM-2 (inactive CORM-2) group. Survival rates were determined after 72 h. Twenty-four similarly treated mice (n = 6 in each group) were assayed for post-operative continuous blood glucose in the first 36 h. Thirty-six similarly treated mice (n = 9 in each group) underwent micro-positron emission tomography (PET) scanning after tail vein injection of ¹⁸F-fluorodeoxyglucose (FDG) 24 h after operation. Plasma and liver specimens were collected for assay of liver pathology, alanine transaminase (ALT) and aspartate transaminase (AST) activities. Hepatic glucokinase activity, lactic acid levels and mitochondrial swelling were also determined.

RESULTS: Improved survival was observed in CORM-2 treated mice. Both the CLP and CLP + CORM-2 groups had sustained low blood glucose levels within the first post-operative 36 h. ¹⁸F-FDG micro-PET images showed abnormally high levels of hepatic glucose metabolism (standardized uptake value) in the CLP group (2.76 ± 0.39 vs 0.84 ± 0.14, P < 0.01), which declined to normal levels after CORM-2 intervention (1.29 ± 0.32 vs 2.76 ± 0.39, P < 0.05). glucokinase activity was markedly increased in the CLP group (6.38 ± 0.56 U/g vs 4.60 ± 0.21 U/g, P < 0.01), but was normal after CORM-2 intervention (4.74 ± 0.14 U/g vs 6.38 ± 0.56 U/g, P < 0.05). CORM-2 suppressed plasma lactic acid levels (4.02 ± 0.02 mmol/L vs 7.72 ± 2.37 mmol/L, P < 0.05) and protected hepatic mitochondria in CLP mice. CORM-2 intervention also reduced elevated plasma AST (199.67 ± 11.08 U/L vs 379.67 ± 16.34 U/L, P < 0.05) and ALT (63.67 ± 12.23 U/L vs 112.67 ± 9.74 U/L, P < 0.05) activities in CLP mice.

CONCLUSION: The release of CO molecules by CORM-2 protects mitochondria and maintains a stable level of hepatic glucose metabolism. Thus, CORM-2 improves liver function and survival in septic mice.

Comparison of whole-body PET/CT and PET/MRI in breast cancer patients: lesion detection and quantitation of 18F-deoxyglucose uptake in lesions and in normal organ tissues

PURPOSE

To compare the performance of PET/MRI imaging using MR attenuation correction (MRAC) (DIXON-based 4-segment -map) in breast cancer patients with that of PET/CT using CT-based attenuation correction and to compare the quantification accuracy in lesions and in normal organ tissues.

METHODS

A total of 36 patients underwent a whole-body PET/CT scan 1h after injection and an average of 62 min later a second scan using a hybrid PET/MRI system. PET/MRI and PET/CT were compared visually by rating anatomic allocation and image contrast. Regional tracer uptake in lesions was quantified using volumes of interest, and maximal and mean standardized uptake values (SUVmax and SUVmean, respectively) were calculated. Metabolic tumor volume (MTV) of each lesion was computed on PET/MRI and PET/CT. Tracer uptake in normal organ tissue was assessed as SUVmax and SUVmean in liver, spleen, left ventricular myocardium, lung, and muscle.

RESULTS

Overall 74 FDG positive lesions were visualized by both PET/CT and PET/MRI. No significant differences in anatomic allocation scores were found between PET/CT and PERT/MRI, while contrast score of lesions on PET/MRI was significantly higher. Both SUVmax and SUVmean of lesions were significantly higher on PET/MRI than on PET/CT, with strong correlations between PET/MRI and PET/CT data (ρ=0.71-0.88). MTVs of all lesions were 4% lower on PET/MRI than on PET/CT, but no statistically significant difference was observed, and an excellent correlation between measurements of MTV with PET/MRI and PET/CT was found (ρ=0.95-0.97; p<0.0001). Both SUVmax and SUVmean were significantly lower by PET/MRI than by PET/CT for lung, liver and muscle, no significant difference was observed for spleen, while either SUVmax and SUVmean of myocardium were significantly higher by PET/MRI. High correlations were found between PET/MRI and PET/CT for both SUVmax and SUVmean of the left ventricular myocardium (ρ=0.91; p<0.0001), while moderate correlations were found for the other normal organ tissues (ρ=0.36-0.61; p<0.05).

CONCLUSIONS

PET/MRI showed equivalent performance in terms of qualitative lesion detection to PET/CT. Despite significant differences in tracer uptake quantification, due to either methodological and biological factors, PET/MRI and PET/CT measurements in lesions and normal organ tissues correlated well. This study demonstrates that integrated whole-body PET/MRI is feasible in a clinical setting with high quality and in a short examination time.

Folate-based radiotracers for PET imaging--update and perspectives

The folate receptor (FR) is expressed in many tumor types, among those ovarian and lung cancer. Due to the high FR affinity of folic acid, it has been used for targeting of FR-positive tumors, allowing specific delivery of attached probes to the malignant tissue. Therefore, nuclear imaging of FR-positive cancer is of clinical interest for selecting patients who could benefit from innovative therapy concepts based on FR-targeting. Positron emission computed tomography (PET) has become an established technique in clinical routine because it provides an increased spatial resolution and higher sensitivity compared to single photon emission computed tomography (SPECT). Therefore, it is of critical importance to develop folate radiotracers suitable for PET imaging. This review article updates on the design, preparation and pre-clinical investigation of folate derivatives for radiolabeling with radioisotopes for PET. Among those the most relevant radionuclides so far are fluorine-18 (t_1/2: 110 min, E_avβ⁺: 250 keV) and gallium-68 (t_1/2: 68 min, E_av β⁺: 830 keV). Recent results obtained with new PET isotopes such as terbium-152 (t_1/2: 17.5 h, Eβ⁺: 470 keV) or scandium-44 (t_1/2: 3.97 h, E_av β⁺: 632 keV) are also presented and discussed. Current endeavors for clinical implementation of PET agents open new perspectives for identification of FR-positive malignancies in patients.

Evaluation of the endothelial function in hypertensive patients with 13N-ammonia PET

BACKGROUND

Essential hypertension is one of the main risk factors for the development of coronary artery disease (CAD). Hypertension causes endothelial dysfunction which is considered an early sign for the development of CAD. Positron emission tomography is a non-invasive imaging technique that measures myocardial blood flow (MBF), allowing us to identify patients with endothelial dysfunction.

METHODS AND RESULTS

19 patients without comorbidities recently diagnosed hypertensive, as well as 21 healthy volunteers were studied. A three-phase (rest, cold pressor test, and adenosine-induced hyperemia) (13)N-ammonia PET was performed, and MBF was measured. Endothelial-Dependent Vasodilation Index, ΔMBF, and coronary flow reserve (CFR) were calculated for each patient. Hypertensive patients had a significantly higher systolic and diastolic blood pressures compared with the control group (134.6 ± 11.7/86.4 ± 10.6 mm Hg and 106.0 ± 11.8/71.4 ± 6.6 mm Hg, respectively, P < .001). The ENDEVI (1.28 ± 0.26 vs 1.79 ± 0.30, P < .001), the ΔMBF (0.81 ± 0.50 vs 0.25 ± 0.21, P < .001) and the CFR (2.18 ± 0.88 vs 3.17 ± 0.68, P = .001) were significantly lower in the hypertensive patients compared to the control group, 84% of the former group had endothelial dysfunction i.e., ENDEVI < 1.5 and 58% had vasomotor abnormalities, i.e., CFR < 2.5.

CONCLUSIONS

In this study, we showed that recently diagnosed hypertensive patients have coronary endothelial dysfunction and vasomotor disturbances which are early signs for the development of CAD.

That liver lesion on MDCT in the oncology patient: is it important?

Multidetector-row computed tomography (MDCT) has become the primary imaging test for the staging and follow-up of most malignancies that originate outside of the central nervous system. Technical advances in this imaging technique have led to significant improvement in the detection of metastatic disease to the liver. An unintended by-product of this improving diagnostic acumen is the discovery of incidental hepatic lesions in oncology patients that in the past remained undetected. These ubiquitous, incidentally identified hepatic lesions have created a management dilemma for both clinicians and radiologists: are these lesions benign or do they represent metastases? Naturally, the answer to this question has profound prognostic and therapeutic implications. In this review, guidelines concerning the diagnosis and management of some of the more common hepatic incidental lesions detected in patients with extrahepatic malignancies are presented.

Prognostic Significance of Volume-based Metabolic Parameters by (18)F-FDG PET/CT in Gallbladder Carcinoma

PURPOSE

We investigated the prognostic values of volume-based metabolic parameters by (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET)/computed tomography (CT) in gallbladder carcinoma patients and compared them with other prognostic parameters.

MATERIALS AND METHODS

We enrolled 44 patients, who were initially diagnosed with gallbladder carcinoma and undergoing (18)F-FDG PET/CT. Various metabolic volume-based PET parameters of primary tumors, including maximum and average standardized uptake values (SUVmax, SUVavg), metabolic tumor volume (MTV), and total lesion glycolysis (TLG), were measured in gallbladder carcinoma patients using mediastinal blood pool activity as a threshold SUV for determining the tumor boundaries. Overall survival analysis was performed using the Kaplan-Meier method with PET parameters and other clinical variables. For determining independent prognostic factors, Cox proportional hazards regression analysis was performed.

RESULTS

Of the 44 enrolled patients, cancer- or treatment-related death occurred in 30 (68.2 %). The mean clinical follow-up period was 22.2 ± 10.4 m (range, 0.6-35.9 m). Univariate analysis demonstrated that clinical or pathologic TNM stage (P < 0.001), treatment modality (P < 0.001), MTV (cutoff = 135 cm(3), P = 0.001), and TLG (cutoff = 7,090, P < 0.05) were significant prognostic factors. In multivariate analysis, both clinical or pathologic TNM stage [hazard ratio (HR) = 2.019 (I vs II), 21.287 (I vs III), and 24.354 (I vs IV); P = 0.001) and TLG (HR = 2.930; P < 0.05) were independent prognostic factors for predicting overall survival.

CONCLUSIONS

In gallbladder cancer, TLG of the primary tumor, a volume-based metabolic parameter, is a significant independent prognostic factor for overall survival in conjunction with the clinical or pathological TNM stage.

Intense FDG Uptake around the Inguinal Surgical Mesh 5 Years after Operation: Case Report and Review of the Literature

We present the case of a 40-year-old man who underwent a FDG PET/CT study for restaging of renal cell carcinoma treated with left nephrectomy, for suspected metastasis in lung and retroperitoneal lymph nodes. The patient had a history of left inguinal hernia repair with implantation of mesh prosthesis 5 years ago. PET/CT image revealed linear intense FDG uptake in left inguinal region most likely corresponding to a persistent foreign body reaction. In this article, a case with an intense FDG uptake around mesh prosthesis after many years was reported, and a summary of the literature about surgical mesh and foreign body reaction causing FDG uptake was reviewed.

CONFLICT OF INTEREST

None declared.

Meta-analysis: comparison of F-18 fluorodeoxyglucose-positron emission tomography and bone scintigraphy in the detection of bone metastasis in patients with lung cancer

RATIONALE AND OBJECTIVES

The aim of this review was to evaluate the diagnostic properties of (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) or PET/computed tomography (CT) and bone scintigraphy in the detection of osseous metastases in patients with lung cancer.

MATERIALS AND METHODS

MEDLINE was searched for relevant original articles published between January 1995 and August 2010. Inclusion criteria were as follows: FDG-PET or PET/CT and bone scintigraphy was carried out to detect bone metastases in patients with lung cancer, sufficient data were presented to construct a 2 × 2 contingency table, and histopathologic analysis and/or close clinical and imaging follow-up and/or radiographic confirmation by multiple imaging modalities was used as the reference standard. Two reviewers independently extracted data related to research design, sample size, imaging techniques, technical characteristics, reference standards, methods of imaging interpretation, and totals of true-positives, false-positives, true-negatives, and false-negatives. Stata was used to obtain per patient and per lesion pooled estimates of sensitivity, specificity, and positive and negative likelihood ratios, and areas under summary receiver-operating characteristic curves (AUCs) were calculated.

RESULTS

The pooled patient-based sensitivity of FDG-PET or PET/CT was 0.93 (95% confidence interval [CI], 0.88-0.96), specificity was 0.95 (95% CI, 0.91-0.98), and the AUC was 0.94. The pooled sensitivity of bone scans was 0.87 (95% CI, 0.79-0.93), specificity was 0.82 (95% CI, 0.62-0.92), and the AUC was 0.91. The pooled lesion-based sensitivity of FDG-PET or PET/CT was 0.93 (95% CI, 0.84-0.97), specificity was 0.91 (95% CI, 0.80-0.96), and the AUC was 0.97. The pooled sensitivity of bone scans was 0.92 (95% CI, 0.87-0.95), specificity was 0.57 (95% CI, 0.09-0.95), and the AUC was 0.92.

CONCLUSIONS

Although FDG-PET or PET/CT has higher sensitivity and specificity than bone scintigraphy, further research with a less biased design is needed to determine the most efficacious imaging modality for the detection of metastatic lung cancer.

New frontiers in neuroimaging applications to inborn errors of metabolism

Most inborn errors of metabolism (IEMs) are associated with potential for injury to the developing central nervous system resulting in chronic encephalopathy, though the etiopathophysiology of neurological injury have not been fully established in many disorders. Shared mechanisms can be envisioned such as oxidative injury due to over-activation of N-Methyl-d-Aspartate (NMDA) receptors with subsequent glutamatergic damage, but other causes such as energy depletion or inflammation are possible. Neuroimaging has emerged as a powerful clinical and research tool for studying the brain in a noninvasive manner. Several platforms exist to study neural networks underlying cognitive processes, white matter/myelin microstructure, and cerebral metabolism in vivo. The scope and limitations of these methods will be discussed in the context of valuable information they provide in the study and management of selected inborn errors of metabolism. This review is not meant to be an exhaustive coverage of diagnostic findings on MRI in multiple IEMs, but rather to illustrate how neuroimaging modalities beyond T1 and T2 images, can add depth to an understanding of the underlying brain changes evoked by the selected IEMs. Emphasis will be placed on techniques that are available in the clinical setting. Though technically complex, many of these modalities have moved - or soon will - to the clinical arena.

Positron emission tomography in patients with suspected pacing system infections may play a critical role in difficult cases

BACKGROUND

A pacemaker recipient may be hospitalized recurrently with an infection of unknown origin despite detailed investigations.

OBJECTIVE

The purpose of this study was to investigate whether (18)F-fluorodeoxyglucose positron emission tomography/computerized tomography (FDG-PET/CT) scanning has a role in identifying pacing material infection in these difficult cases.

METHODS

Ten patients who presented with fever of unknown origin despite detailed investigations including transesophageal echocardiography underwent FDG-PET/CT scanning. Identification of increased FDG uptake along a pacing lead prompted the removal of the entire pacing system, whereas in the absence of increased FDG uptake the pacing material was left in place. Forty control pacemaker recipients underwent FDG-PET/CT scanning as part of investigation of malignancy.

RESULTS

Among the 40 patients in the control group, FDG-PET/CT scanning was normal in 37 (92.5%) patients. Among the 10 patients who presented with suspected pacing system infections, FDG-PET/CT scanning showed increased FDG uptake along a lead in six patients; as a result of this finding, these patients subsequently underwent complete removal of the implanted material. Cultures of the leads were positive in all six patients, confirming involvement of the leads in the infectious process. In the other four patients, the pacing system was left in place without objective signs of active lead endocarditis during follow-up.

CONCLUSION

This study demonstrates the potential value of FDG-PET/CT scanning in the diagnosis of pacing lead endocarditis in difficult cases. Increased FDG uptake along a lead in this clinical context appears to be a reliable sign of active infection.

Molecular imaging in radiotherapy planning for head and neck tumors

Molecular imaging uses noninvasive techniques to visualize various biologic pathways and physiologic characteristics of tumors and normal tissues. In relation to radiation therapy, PET with the tracer (18)F-FDG offers a unique opportunity to refine the target volume delineation in patients with squamous cell carcinoma of the head and neck, in turn affecting dose distribution and, it is hoped, patient outcome. Even more so, in the framework of adaptive treatment and theragnostics, whereby dose distribution is adapted in space and time over the typical course of radiotherapy, molecular imaging with PET offers an elegant research avenue to further improve the therapeutic ratio. Such implementation could be of particular interest with tracers other than (18)F-FDG, such as tracers of hypoxia and proliferation.

Preclinical Studies with Small Animal PET

Because no effective cures are available for cutaneous malignant melanoma, early diagnosis and accurate staging are of the utmost importance in increasing patient survival. Fluorodeoxyglucose positron emission tomography (PET)/computed tomography is a functional imaging technique that has contributed to ameliorating surveillance of patients with melanoma. New PET probes are under evaluation, and many have been tried in in vivo imaging protocols based on the use of small animal PET and animal models of cutaneous melanoma. Those compounds are targeted to a-melanocyte-stimulating hormone receptor and to the intracellular biosynthesis of melanin, and all of them showed promising results.

Molecular imaging: current status and emerging strategies

In vivo molecular imaging has a great potential to impact medicine by detecting diseases in early stages (screening), identifying extent of disease, selecting disease- and patient-specific treatment (personalized medicine), applying a directed or targeted therapy, and measuring molecular-specific effects of treatment. Current clinical molecular imaging approaches primarily use positron-emission tomography (PET) or single photon-emission computed tomography (SPECT)-based techniques. In ongoing preclinical research, novel molecular targets of different diseases are identified and, sophisticated and multifunctional contrast agents for imaging these molecular targets are developed along with new technologies and instrumentation for multi-modality molecular imaging. Contrast-enhanced molecular ultrasound (US) with molecularly-targeted contrast microbubbles is explored as a clinically translatable molecular imaging strategy for screening, diagnosing, and monitoring diseases at the molecular level. Optical imaging with fluorescent molecular probes and US imaging with molecularly-targeted microbubbles are attractive strategies as they provide real-time imaging, are relatively inexpensive, produce images with high spatial resolution, and do not involve exposure to ionizing irradiation. Raman spectroscopy/microscopy has emerged as a molecular optical imaging strategy for ultrasensitive detection of multiple biomolecules/biochemicals with both in vivo and ex vivo versatility. Photoacoustic imaging is a hybrid of optical and US techniques involving optically-excitable molecularly-targeted contrast agents and quantitative detection of resulting oscillatory contrast agent movement with US. Current preclinical findings and advances in instrumentation, such as endoscopes and microcatheters, suggest that these molecular imaging methods have numerous potential clinical applications and will be translated into clinical use in the near future.

High-contrast PET of melanoma using (18)F-MEL050, a selective probe for melanin with predominantly renal clearance

The aim of this study was to evaluate the novel probe (18)F-6-fluoro-N-[2-(diethylamino)ethyl] pyridine-3-carboxamide ((18)F-MEL050) for the imaging of primary and metastatic melanoma.

METHODS

PET using (18)F-MEL050 was performed in murine models of melanoma. The specificity of (18)F-MEL050 was studied by comparing its accumulation in pigmented B16-F0 allograft tumors with that of human amelanotic A375 xenografts using PET and high-resolution autoradiography. (18)F-MEL050 PET results were compared with (18)F-FDG PET, the current standard in melanoma molecular imaging. To test the ability of (18)F-MEL050 to assess the metastatic spread of melanoma, a murine model of lung metastasis was imaged by PET/CT, and results correlated with physical assessment of tumor burden in the lungs.

RESULTS

In pigmented B16-F0 grafts, (18)F-MEL050 PET yielded a tumor-to-background ratio of approximately 20:1 at 1 h and greater than 50:1 at 2 and 3 h. In the B16-F0 melanoma allograft model, tumor-to-background ratio was more than 9-fold higher for (18)F-MEL050 than for (18)F-FDG (50.9 +/- 6.9 vs. 5.8 +/- 0.5). No uptake was observed in the amelanotic melanoma xenografts. Intense uptake of (18)F-MEL050 was evident in metastatic lesions in the lungs of B16-BL6 tumor-bearing mice on PET at 2 h after tracer injection, with high concordance between (18)F-MEL050 accumulation on PET/CT and tumor burden determined at necroscopy.

CONCLUSION

(18)F-MEL050 has a rapid tumor uptake and high retention with specificity for melanin, suggesting great potential for noninvasive clinical evaluation of suspected metastatic melanoma.

The role of PET-CT in patients with incidental gallbladder cancer

INTRODUCTION

After a cholecystectomy, incidental gallbladder cancer (IGC) requires accurate imaging studies to determine the actual extent of the disease to properly tailor subsequent treatment. The aim of this study was to evaluate the utility of (18)F-fluorodeoxyglucose positron emission tomography-computed tomography ((18)FDG PET-CT) to provide optimal pre-treatment staging in patients with IGC.

MATERIAL AND METHODS

Between January 2006 and August 2008, all patients with IGC and at least muscular layer invasion were studied with (18)FDG PET-CT. The examination was considered positive when the standardized uptake values (SUV) were >/=2.5. In all instances patients were offered to undergo definitive exploration and possible radical resection.

RESULTS

The series included 32 patients, 26 women and 6 men, with a median age of 57 years (range 30-81 years). The examination was performed at a median time of 6 weeks after cholecystectomy (range 2-52 weeks). (18)FDG PET-CT was negative in 13 patients and positive in 19 patients: 9 with localized potentially resectable disease (PRD) and in 10 with disseminated disease. Of the 13 patients with negative PET-CT, 9 refused surgery and 4 underwent formal exploration: 3 patients were resected with no disease identified in the final pathology report (FPR) and 1 was not resected as a result of peritoneal carcinomatosis. Of the 9 with PRD, 4 patients refused reoperation and 5 underwent exploration: 3 were resected with residual disease noted in the FPR and 2 did not undergo resection because of dissemination. Two patients with disseminated disease were reoperated and in both instances disseminated disease was confirmed. The median survival for the entire group was 20.3 months (range 1.6-32.9 months). The median survival for those patients with negative PET-CT was 13.5 months (range 5.6-32.9 months), 6.2 months (range 1.6-18.7 months) for localized potentially resectable disease and 4.9 months (range 2-14.1 months) for disseminated disease (P < 0.003).

CONCLUSIONS

For patients presenting with stage T1b or greater IGC, the use of (18)FDG PET-CT will help reduce the number of patients undergoing non-therapeutic re-exploration and may help to determine the likely prognosis. (18)FDG PET-CT might be a useful tool for the selection of patients for potentially curative treatment.