Monte Carlo simulations and radiation dosimetry measurements of 142Pr capillary tube-based radioactive implant (CTRI): a new structure for brachytherapy sources

Objective

Previously, a promising $ {\beta^- } $ -emitting praseodymium-142 glass seed was proposed for brachytherapy of prostate cancer. In accordance with the previous study, a ¹⁴²Pr capillary tube-based radioactive implant (CTRI) was suggested as a source with a new structure to enhance application of $ {\beta^- } $ -emitting radioisotopes such as ¹⁴²Pr in brachytherapy.

Methods

Praseodymium oxide powder was encapsulated in a glass capillary tube. Then, a thin and flexible fluorinated ethylene propylene Teflon^® layer sealed the capillary tube. The source was activated in the Tehran Research Reactor by the ¹⁴¹Pr(n,γ) ¹⁴²Pr reaction. Measurements of the dosimetric parameters were performed using GafChromic^® radiochromic film. In addition, the dose rate distribution of ¹⁴²Pr CTRI was calculated by modeling ¹⁴²Pr source in a water phantom using Monte Carlo N-Particle Transport (MCNP5) Code.

Results

The active source was unreactive and did not leak in water. In comparison with the earlier proposed ¹⁴²Pr seed, the suggested source showed similar desirable dosimetric characteristics. Moreover, the ¹⁴²Pr CTRI production procedure may be technically and economically more feasible. The mass of praseodymium in CTRI structure could be greater than that of the ¹⁴²Pr glass seed; therefore, the required irradiation time and the neutron flux could be reduced.

Conclusion

A ¹⁴²Pr CTRI was proposed for brachytherapy of prostate cancer. The dosimetric calculations by the experimental measurements and Monte Carlo simulation were performed to fulfill the requirements according to the American Association of Physicists in Medicine recommendations before the clinical use of new brachytherapy sources. The characteristics of the suggested source were compared with those of the previously proposed ¹⁴²Pr glass seed.     

��v��3 imaging can accurately distinguish between mature teratoma and necrosis in 18F-FDG-negative residual masses after treatment of non-seminomatous testicular cancer: a preclinical study

Purpose

We assessed whether imaging ??_v??₃ integrin could distinguish mature teratoma from necrosis in human non-seminomatous germ cell tumour (NSGCT) post-chemotherapy residual masses.

Methods

Human embryonal carcinoma xenografts (six/rat) were untreated (controls) or treated to form mature teratomas with low-dose cisplatin and all-trans retinoic acid (ATRA) over a period of 8?weeks. In another group, necrosis was induced in xenografts with high-dose cisplatin plus etoposide (two cycles).¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) small animal positron emission tomography (SA PET) imaging was performed in three rats (one control and two treated for 4 and 8?weeks with cisplatin+ATRA). Imaging of ??_v??₃ expression was performed in six rats bearing mature teratomas and two rats with necrotic lesions on a microSPECT/CT device after injection of the tracer [^99mTc]HYNIC-RGD [6-hydrazinonicotinic acid conjugated to cyclo(Arg-Gly-Asp-D-Phe-Lys)]. Correlative immunohistochemistry studies of human and mouse ??_v??₃ expression were performed.

Results

Cisplatin+ATRA induced differentiation of the xenografts. After 8?weeks, some glandular structures and mesenchymal cells were visible; in contrast, control tumours showed undifferentiated tissues. SA PET imaging showed that mature teratoma had very low avidity for ¹⁸F-FDG [mean standardised uptake value (SUV_mean)?=?0.48?±?0.05] compared to untreated embryonal carcinoma (SUV_mean?=?0.92?±?0.13) (p?=?0.005). ??_v??₃ imaging accurately distinguished mature teratoma (tumour to muscle ratio?=?4.29?±?1.57) from necrosis (tumour to muscle ratio?=?1.3?±?0.26) (p?=?0.0002). Immunohistochemistry studies showed that ??_v??₃ integrin expression was strong in the glandular structures of mature teratoma lesions and negative in host stroma.

Conclusion

Imaging ??_v??₃ integrin accurately distinguished mature teratoma from necrosis following cisplatin-based treatment in human NSGCT xenografts.     

Diet intervention reduces uptake of αvβ3 integrin-targeted PET tracer 18F-galacto-RGD in mouse atherosclerotic plaques

Background

Expression of ??_v??₃ integrin has been proposed as a marker for atherosclerotic lesion inflammation. We studied whether diet intervention reduces uptake of ??_v??₃ integrin-targeted positron emission tomography tracer ¹⁸F-galacto-RGD in mouse atherosclerotic plaques.

Methods and Results

Hypercholesterolemic LDLR^?/? ApoB^100/100 mice on high-fat diet for 4?months were randomized to further 3?months on high-fat diet (high-fat group, n?=?8) or regular mouse chow (intervention group, n?=?7). Intima-media ratio describing plaque burden was comparable between intervention and high-fat groups (2.0?±?0.5 vs 2.3?±?0.8, P?=?.5). Uptake of ¹⁸F-galacto-RGD in the aorta was lower in the intervention than high-fat group (%ID/g 0.16 vs 0.23, P?<?.01). Autoradiography showed 35% lower uptake of?¹⁸F-galacto-RGD in the atherosclerotic plaques in the intervention than high-fat group (P?=?.007). Uptake of ¹⁸F-galacto-RGD in plaques correlated with uptake of ³H-deoxyglucose and nuclear density, which was lower in the intervention than high-fat group (P?=?.01). Flow cytometry demonstrated macrophages expressing ??_v and ??₃ integrins in the aorta.

Conclusions

Uptake of ¹⁸F-galacto-RGD in mouse atherosclerotic lesions was reduced by lipid-lowering diet intervention. Expression of ??_v??₃ integrin is a potential target for evaluation of therapy response in atherosclerosis.     

Quality control within the multicentre perfusion CT study of primary colorectal cancer (PROSPeCT): results of an iodine density phantom study

Objectives

To assess the cross-centre consistency of iodine enhancement, contrast-to-noise ratio and radiation dose in a multicentre perfusion CT trial of colorectal cancer.

Materials and methods

A cylindrical water phantom containing different iodine inserts was examined on seven CT models in 13 hospitals. The relationship between CT number (Hounsfield units, HU) and iodine concentration (milligrams per millilitre) was established and contrast-to-noise ratios (CNRs) calculated. Radiation doses (CTDI_vol, DLP) were compared across all sites.

Results

There was a linear relationship between CT number and iodine density. Iodine enhancement varied by a factor of at most 1.10, and image noise by at most 1.5 across the study sites. At an iodine concentration of 1 mg ml^?1 and 100 kV, CNRs ranged from 3.6 to 4.8 in the 220-mm phantom and from 1.4 to 1.9 in the 300-mm phantom. Doses varied by a factor of at most 2.4, but remained within study dose constraints. Iterative reconstruction algorithms did not alter iodine enhancement but resulted in reduced image noise by a factor of at most 2.2, allowing a potential dose decrease of at most 80 % compared to filtered back projection (FBP).

Conclusions

Quality control of CT performance across centres indicates that CNR values remain relatively consistent across all sites, giving acceptable image quality within the agreed dose constraints.

Key Points

? Quality control is essential in a multicentre setting to enable CT quantification. ? CNRs in a body-sized phantom had the recommended value of at least 1.5. ? CTDIs and DLPs varied by factors of 1.8 and 2.4 respectively.     

MRI-based biodistribution assessment of holmium-166 poly(L-lactic acid) microspheres after radioembolisation

Objectives

To demonstrate the feasibility of MRI-based assessment of the intrahepatic Ho-PLLA-MS biodistribution after radioembolisation in order to estimate the absorbed radiation dose.

Methods

Fifteen patients were treated with holmium-166 (¹⁶⁶Ho) poly(L-lactic acid)-loaded microspheres (Ho-PLLA-MS, mean 484 mg; range 408–593 mg) in a phase I study. Multi-echo gradient-echo MR images were acquired from which R ₂ ^* maps were constructed. The amount of Ho-PLLA-MS in the liver was determined by using the relaxivity r ₂ ^* of the Ho-PLLA-MS and compared with the administered amount. Quantitative single photon emission computed tomography (SPECT) was used for comparison with MRI regarding the whole liver absorbed radiation dose.

Results

R ₂ ^* maps visualised the deposition of Ho-PLLA-MS with great detail. The mean total amount of Ho-PLLA-MS detected in the liver based on MRI was 431 mg (range 236–666 mg) or 89?±?19 % of the delivered amount (correlation coefficient r?=?0.7; P?<?0.01). A good correlation was found between the whole liver mean absorbed radiation dose as assessed by MRI and SPECT (correlation coefficient r?=?0.927; P?<?0.001).

Conclusion

MRI-based dosimetry for holmium-166 radioembolisation is feasible. Biodistribution is visualised with great detail and quantitative measurements are possible.

Key Points

? Radioembolisation is increasingly used for treating unresectable primary or metastatic liver tumours. ? MRI-based intrahepatic microsphere biodistribution assessment is feasible after holmium-166 radioembolisation. ? MRI enables quantification of holmium-166 microspheres in liver in a short imaging time. ? MRI can estimate the whole liver absorbed radiation dose following holmium-166 radioembolisation.     

Diffusion weighted imaging of the normal breast: reproducibility of apparent diffusion coefficient measurements and variation with menstrual cycle and menopausal status

Objectives

To establish the reproducibility of apparent diffusion coefficient (ADC) measurements in normal fibroglandular breast tissue and to assess variation in ADC values with phase of the menstrual cycle and menopausal status.

Methods

Thirty-one volunteers (13 premenopausal, 18 postmenopausal) underwent magnetic resonance twice (interval 11–22?days) using diffusion-weighted MRI. ADC_total and a perfusion-insensitive ADC_high (omitting b?=?0) were calculated. Reproducibility and inter-observer variability of mean ADC values were assessed. The difference in mean ADC values between the two phases of the menstrual cycle and the postmenopausal breast were evaluated.

Results

ADC_total and ADC_high showed good reproducibility (r%?=?17.6, 22.4). ADC_high showed very good inter-observer agreement (kappa?=?0.83). The intraclass correlation coefficients (ICC) were 0.93 and 0.91. Mean ADC values were significantly lower in the postmenopausal breast (ADC_total 1.46?±?0.3?×?10^-3?mm²/s, ADC_high 1.33?±?0.3?×?10^-3?mm²/s) compared with the premenopausal breast (ADC_total 1.84?±?0.26?×?10^-3?mm²/s, ADC_high 1.77?±?0.26?×?10^-3?mm²/s; both P?total P?=?0.2, ADC_high P?=?0.24) or between postmenopausal women taking or not taking oestrogen supplements (ADC_total P?=?0.6, ADC_high P?=?0.46).

Conclusions

ADC values in fibroglandular breast tissue are reproducible. Lower ADC values within the postmenopausal breast may reduce diffusion-weighted contrast and have implications for accurately detecting tumours.

Key Points

? ADC values from fibroglandular breast tissue are measured reproducibly by multiple observers. ? Mean ADC values were significantly lower in postmenopausal than premenopausal breast tissue. ? Mean ADC values did not vary significantly with menstrual cycle. ? Low postmenopausal ADC values may hinder tumour detection on DW-MRI.     

Quantification of intracranial internal carotid artery calcification on brain unenhanced CT: evaluation of its feasibility and assessment of the reliability of visual grading scales

Objectives

Previous studies have evaluated intracranial internal carotid artery calcifications (ICACs) qualitatively using different visual grading scales, which could lead to inconsistent results. The purpose of this study was to evaluate the feasibility of ICAC volume measurement and to correlate the volume with visual grading scales.

Methods

We included 49 patients (>50?years) who underwent unenhanced cranial CT. Two observers evaluated four visual grading scales and measured ICAC volumes semi-automatically, and interobserver agreements were assessed. Differences in ICAC volume between visual grades of each scale were tested. The relationship between the visual grading and volume was assessed.

Results

Interobserver agreements ranged from 0.841 to 0.901 for visual grading and 0.997 for volume measurement. Mean volumes were not significantly different between the visual grades (P?>?0.05) except when comparing grade 4 with the other grades. The grades of each visual grading correlated well with ICAC volumes (Spearman's ???=?0.849?C0.881, P?<?0.001). The relationship between the visual grades and volume was described by a quadratic model (R ², 0.31?C0.50, P?<?0.01).

Conclusions

ICAC volume measurement is feasible and reproducible, whereas visual grades poorly reflect the actual volume; therefore, volume measurement may be warranted for future research.

Key Points

? Computed tomography provides unique information about vascular calcification. ? Volume measurement of intracranial carotid artery calcification is feasible and reproducible. ? Visual grades poorly reflect the volume of intracranial carotid artery calcification. ? Quantification of intracranial carotid artery calcification is warranted for future research.     

Sensitivity and accuracy of volumetry of pulmonary nodules on low-dose 16- and 64-row multi-detector CT: an anthropomorphic phantom study

Objective

To assess the sensitivity of detection and accuracy of volumetry by manual and semi-automated quantification of artificial pulmonary nodules in an anthropomorphic thoracic phantom on low-dose CT.

Methods

Fifteen artificial spherical nodules (diameter 3, 5, 8, 10 and 12?mm; CT densities -800, -630 and +100 HU) were randomly placed inside an anthropomorphic thoracic phantom. The phantom was examined on 16- and 64-row multidetector CT with a low-dose protocol. Two independent blinded observers screened for pulmonary nodules. Nodule diameter was measured manually, and volume calculated. For solid nodules (+100 HU), diameter and volume were also evaluated by semi-automated software. Differences in observed volumes between the manual and semi-automated method were evaluated by a t-test.

Results

Sensitivity was 100?% for all nodules of >5?mm and larger, 60?C80?% for solid and 0?C20?% for non-solid 3-mm nodules. No false-positive nodules but high inter-observer reliability and inter-technique correlation were found. Volume was underestimated manually by 24.1?±?14.0?% for nodules of any density, and 26.4?±?15.5?% for solid nodules, compared with 7.6?±?8.5?% (P?<?0.01) semi-automatically.

Conclusion

In an anthropomorphic phantom study, the sensitivity of detection is 100?% for nodules of >5?mm in diameter. Semi-automated volumetry yielded more accurate nodule volumes than manual measurements.

Key Points

? Computed tomography has become the definitive investigation of the chest. ? Low-dose CT techniques have recently been introduced. ? Low-dose CT is reliable for detecting spherical pulmonary nodules of >5?mm. ? Semi-automated volumetry is more accurate than manual measurement for pulmonary nodules. ? No difference in the accuracy of volumetry was found between 16- and 64- MDCT.     

Technical performance evaluation of a human brain PET/MRI system

Objectives

Technical performance evaluation of a human brain PET/MRI system.

Methods

The magnetic field compatible positron emission tomography (PET) insert is based on avalanche photodiode (APD) arrays coupled with lutetium oxyorthosilicate (LSO) crystals and slip-fits into a slightly modified clinical 3-T MRI system. The mutual interference between the two imaging techniques was minimised by the careful design of the hardware to maintain the quality of the B ₀ and B ₁ field homogeneity.

Results

The signal-to-noise ratio (SNR) and the homogeneity of the MR images were minimally influenced by the presence of the PET. Measurements according to the Function Biomedical Informatics Research Network (FBIRN) protocol proved the combined system’s ability to perform functional MRI (fMRI). The performance of the PET insert was evaluated according to the National Electrical Manufacturers Association (NEMA) standard. The noise equivalent count rate (NEC) peaked at 30.7?×?10³?counts/s at 7.3?kBq/mL. The point source sensitivity was greater than 7?%. The spatial resolution in the centre field of view was less than 3?mm. Patient data sets clearly revealed a noticeably good PET and MR image quality.

Conclusion

PET and MRI phantom tests and first patient data exhibit the device’s potential for simultaneous multiparametric imaging.

Key Points

? Combination of PET and MRI is a new emerging imaging technology. ? Evaluated brain PET/MRI enables uncompromised imaging performance. ? PET/MRI aims to provide multiparametric imaging allowing acquisition of morphology and metabolism.     

Comparison of ASL and DCE MRI for the non-invasive measurement of renal blood flow: quantification and reproducibility

Objectives

To investigate the reproducibility of arterial spin labelling (ASL) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) and quantitatively compare these techniques for the measurement of renal blood flow (RBF).

Methods

Sixteen healthy volunteers were examined on two different occasions. ASL was performed using a multi-TI FAIR labelling scheme with a segmented 3D-GRASE imaging module. DCE MRI was performed using a 3D-FLASH pulse sequence. A Bland-Altman analysis was used to assess repeatability of each technique, and determine the degree of correspondence between the two methods.

Results

The overall mean cortical renal blood flow (RBF) of the ASL group was 263?±?41 ml min^?1 [100 ml tissue]^?1, and using DCE MRI was 287?±?70 ml min^?1 [100 ml tissue]^?1. The group coefficient of variation (CV_g) was 18 % for ASL and 28 % for DCE-MRI. Repeatability studies showed that ASL was more reproducible than DCE with CV_gs of 16 % and 25 % for ASL and DCE respectively. Bland-Altman analysis comparing the two techniques showed a good agreement.

Conclusions

The repeated measures analysis shows that the ASL technique has better reproducibility than DCE-MRI. Difference analysis shows no significant difference between the RBF values of the two techniques.

Key Points

? Reliable non-invasive monitoring of renal blood flow is currently clinically unavailable. ? Renal arterial spin labelling MRI is robust and repeatable. ? Renal dynamic contrast-enhanced MRI is robust and repeatable. ? ASL blood flow values are similar to those obtained using DCE-MRI.     

Dynamic contrast enhanced-MRI for the detection of pathological complete response to neoadjuvant chemotherapy for locally advanced rectal cancer

Objective

To determine the ability of dynamic contrast enhanced (DCE-MRI) to predict pathological complete response (pCR) after preoperative chemotherapy for rectal cancer.

Methods

In a prospective clinical trial, 23/34 enrolled patients underwent pre- and post-treatment DCE-MRI performed at 1.5T. Gadolinium 0.1?mmol/kg was injected at a rate of 2?mL/s. Using a two-compartmental model of vascular space and extravascular extracellular space, K^trans, k_ep, v_e, AUC90, and AUC180 were calculated. Surgical specimens were the gold standard. Baseline, post-treatment and changes in these quantities were compared with clinico-pathological outcomes. For quantitative variable comparison, Spearman’s Rank correlation was used. For categorical variable comparison, the Kruskal–Wallis test was used. P?≤?0.05 was considered significant.

Results

Percentage of histological tumour response ranged from 10 to 100%. Six patients showed pCR. Post chemotherapy K^trans (mean 0.5?min^?1 vs. 0.2?min^?1, P?=?0.04) differed significantly between non-pCR and pCR outcomes, respectively and also correlated with percent tumour response and pathological size. Post-treatment residual abnormal soft tissue noted in some cases of pCR prevented an MR impression of complete response based on morphology alone.

Conclusion

After neoadjuvant chemotherapy in rectal cancer, MR perfusional characteristics have been identified that can aid in the distinction between incomplete response and pCR.

Key Points

• Dynamic contrast enhanced (DCE) MRI provides perfusion characteristics of tumours.
• These objective quantitative measures may be more helpful than subjective imaging alone
• Some parameters differed markedly between completely responding and incompletely responding rectal cancers.
• Thus DCE-MRI can potentially offer treatment-altering imaging biomarkers.

     

Quantitative multivoxel proton MR spectroscopy study of brain metabolites in patients with amnestic mild cognitive impairment: a pilot study

Introduction

The purpose of this study is to investigate brain metabolic changes in patients with amnestic mild cognitive impairment (aMCI) using multivoxel proton MR spectroscopy (¹H-MVS).

Methods

Fourteen aMCI patients and fifteen healthy control subjects participated in this experiment. All MR measurements were acquired using a 1.5-T GE scanner. ¹H-MVS point resolved spectroscopy (2D PROBE-CSI PRESS) pulse sequence (TE?=?35?ms; TR?=?1,500?ms; phase?×?frequency, 18?×?18) was used for acquiring MRS data. All data were post-processed using Spectroscopy Analysis by General Electric software and linear combination of model (LCModel). The absolute concentrations of N-acetylaspartate (NAA), choline (Cho), myoinositol (MI), creatine (Cr), and the metabolite ratios of NAA/Cr, Cho/Cr, MI/Cr, and NAA/MI were measured bilaterally in the posterior cingulate gyrus (PCG), inferior precuneus (Pr), paratrigonal white matter (PWM), dorsal thalamus (DT), and lentiform nucleus (LN).

Results

Patients with aMCI displayed significantly lower NAA levels in the bilateral PCG (p?<?0.01), PWM (p?<?0.05), and left inferior Pr (p?<?0.05). The metabolite ratio of NAA/MI was decreased in the bilateral PCG (p?<?0.01) and PWM (p?<?0.05) and in the left DT (p?<?0.01). NAA/Cr was decreased in the left PCG (p?<?0.01), DT (p?<?0.05), right PWM (p?<?0.05), and LN (p?<?0.05). However, MI/Cr was elevated in the right PCG (p?<?0.01) and left PWM (p?<?0.05). Significantly increased Cho level was also evident in the left PWM (p?<?0.05).

Conclusions

Our observations of decreased NAA, NAA/Cr, and NAA/MI, in parallel with increased Cho and MI/Cr might be characteristic of aMCI patients.     

Attenuated right ventricular energetics evaluated using 11C-acetate PET in patients with pulmonary hypertension

Purpose

The right ventricle (RV) has a high capacity to adapt to pressure or volume overload before failing. However, the mechanisms of RV adaptation, in particular RV energetics, in patients with pulmonary hypertension (PH) are still not well understood. We aimed to evaluate RV energetics including RV oxidative metabolism, power and efficiency to adapt to increasing pressure overload in patients with PH using ¹¹C-acetate PET.

Methods

In this prospective study, 27 patients with WHO functional class II/III PH (mean pulmonary arterial pressure 39.8?±?13.5 mmHg) and 9 healthy individuals underwent ¹¹C-acetate PET. ¹¹C-acetate PET was used to simultaneously measure oxidative metabolism (k _mono) for the left ventricle (LV) and RV. LV and RV efficiency were also calculated.

Results

The RV ejection fraction in PH patients was lower than in controls (p?=?0.0054). There was no statistically significant difference in LV k _mono (p?=?0.09). In contrast, PH patients showed higher RV k _mono than did controls (0.050?±?0.009 min^?1 vs. 0.030?±?0.006 min^?1, p?<?0.0001). PH patients exhibited significantly increased RV power (p?<?0.001) and hence increased RV efficiency compared to controls (0.40?±?0.14 vs. 0.017?±?0.12 mmHg·mL·min/g, p?=?0.001).

Conclusion

The RV oxidative metabolic rate was increased in patients with PH. Patients with WHO functional class II/III PH also had increased RV power and efficiency. These findings may indicate a myocardial energetics adaptation response to increasing pulmonary arterial pressure.     

18F-FAMT in patients with multiple myeloma: clinical utility compared to 18F-FDG

Objective

l-[3-¹⁸F]-alpha-methyltyrosine (¹⁸F-FAMT) is an amino-acid tracer for positron emission tomography (PET), with uptake related to overexpression of L-type amino-acid transporter 1 and proliferative activity in tumour cells. This study evaluated the diagnostic performance of ¹⁸F-FAMT PET compared with 2-[¹⁸F]-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) PET in patients with multiple myeloma (MM).

Methods

Eleven patients with MM (newly diagnosed, n?=?3; relapsed after treatment, n?=?8) underwent whole-body ¹⁸F-FAMT and ¹⁸F-FDG PET within a 2-week interval. Magnetic resonance imaging (MRI) of the spine was also performed to assess patterns of bone marrow infiltration. Tracer uptake was semi-quantitatively evaluated using maximal standardized uptake value (SUV_max). Mean SUV was also determined for normal bone marrow and the aortic arch as mediastinal background SUV to calculate lesion-to-bone marrow (L/B) and lesion-to-mediastinum (L/M) ratios, respectively. Those values were statistically compared using Student??s t test.

Results

In 8 patients showing focal infiltration on MRI, 34 FDG-avid bone lesions were identified, with each showing increased FAMT uptake. Mean SUV_max and L/B ratio of FDG (3.1?±?1.2 and 3.3?±?1.9, respectively) were significantly higher than those of FAMT (2.0?±?1.0 and 2.6?±?1.1, respectively; p?<?0.05 each). In contrast, the L/M ratio of FDG showed no significant difference to that of FAMT (2.2?±?1.0 and 2.4?±?1.2, respectively; p?=?0.3).

Conclusions

Clear ¹⁸F-FAMT PET uptake was seen in most ¹⁸F-FDG-avid lesions among patients with MM, and an equivalent semi-quantitative value was obtained using L/M ratio. Our preliminary data suggest that ¹⁸F-FAMT PET provides a useful imaging modality for detecting active myelomatous lesions.     

Grading of supratentorial astrocytic tumors by using the difference of ADC value

Introduction

To investigate the application value of diffusion-weighted imaging (DWI), the difference of apparent diffusion coefficient (ADC_difference) value calculated from ADC_difference map was used, in evaluating the pathologic grade of astrocytic tumors.

Methods

33 patients with histopathologically proven supratentorial astrocytic tumors were included in this prospective study. All of them received conventional magnetic resonance imaging (MRI), DWI with diffusion factor of 0 and 50?s/mm² and of 0 and 3,000?s/mm², and perfusion-weighted imaging (PWI) examinations. Pseudo-color ADC_difference maps were obtained by means of using ADC map with low b value (0 and 50?s/mm²) minus ADC map with high b value (0 and 3,000?s/mm²).

Results

The highest ADC_difference value of grades I?CII, grade III, and grade IV was (0.91?±?0.07)?×?10^?3, (1.81?±?0.38)?×?10^?3, and (2.36?±?0.32)?×?10^?3 mm²/s, respectively, and there was statistical difference among them (p?<?0.001). The highest ADC_difference value between low-grade (grades I?CII) and high-grade (grades III?CIV) astrocytic tumors showed statistical difference as well (p?<?0.001). The highest ADC_difference value of astrocytic tumors correlated positively with the pathologic grade of tumor (r?=?0.853, p?<?0.001). Positive correlation was found between the highest ADC_difference value and maximum relative cerebral blood volume (rCBV) value (r?=?0.829, p?<?0.001) in high-grade astrocytic tumors; however, the highest ADC_difference value and maximum rCBV value had no significant correlation in low-grade astrocytic tumors (r?=?0.259, p?=?0.536).

Conclusion

Quantitative analysis of highest ADC_difference value of supratentorial astrocytic tumors may provide valuable information of tumor microcirculation and perfusion, thus allowing a promising new method for preoperatively assessing the pathologic grade of tumor.     

High throughput static and dynamic small animal imaging using clinical PET/CT: potential preclinical applications

Purpose

The objective of the study was to evaluate state-of-the-art clinical PET/CT technology in performing static and dynamic imaging of several mice simultaneously.

Methods

A mouse-sized phantom was imaged mimicking simultaneous imaging of three mice with computation of recovery coefficients (RCs) and spillover ratios (SORs). Fifteen mice harbouring abdominal or subcutaneous tumours were imaged on clinical PET/CT with point spread function (PSF) reconstruction after injection of [18F]fluorodeoxyglucose or [18F]fluorothymidine. Three of these mice were imaged alone and simultaneously at radial positions –5, 0 and 5 cm. The remaining 12 tumour-bearing mice were imaged in groups of 3 to establish the quantitative accuracy of PET data using ex vivo gamma counting as the reference. Finally, a dynamic scan was performed in three mice simultaneously after the injection of ⁶⁸Ga-ethylenediaminetetraacetic acid (EDTA).

Results

For typical lesion sizes of 7–8 mm phantom experiments indicated RCs of 0.42 and 0.76 for ordered subsets expectation maximization (OSEM) and PSF reconstruction, respectively. For PSF reconstruction, SOR_air and SOR_water were 5.3 and 7.5%, respectively. A strong correlation (r ²?=?0.97, p?<?0.0001) between quantitative data obtained in mice imaged alone and simultaneously in a group of three was found following PSF reconstruction. The correlation between ex vivo counting and PET/CT data was better with PSF reconstruction (r ²?=?0.98; slope?=?0.89, p?<?0.0001) than without (r ²?=?0.96; slope?=?0.62, p?<?0.001). Valid time-activity curves of the blood pool, kidneys and bladder could be derived from ⁶⁸Ga-EDTA dynamic acquisition.

Conclusion

New generation clinical PET/CT can be used for simultaneous imaging of multiple small animals in experiments requiring high throughput and where a dedicated small animal PET system is not available.     

Preoperative lymph node staging in patients with primary prostate cancer: comparison and correlation of quantitative imaging parameters in diffusion-weighted imaging and 11C-choline PET/CT

Purpose

To compare the diagnostic performance of DWI and 11C-choline PET/CT in the assessment of preoperative lymph node status in patients with primary prostate cancer.

Material and methods

Thirty-three patients underwent DWI and 11C-choline PET/CT prior to prostatectomy and extended pelvic lymph node dissection. Mean standardised uptake value (SUV_mean) and mean apparent diffusion coefficient (ADC) of 76 identified lymph nodes (LN) were measured and correlated with histopathology. ADC values and SUVs were compared using linear regression analysis.

Results

A significant difference between benign and malignant LN was observed for ADC values (1.17 vs. 0.96?×?10^-3 mm²/s; P?<?0.001) and SUV_mean (1.61 vs. 3.20; P?<?0.001). ROC analysis revealed an optimal ADC threshold of 1.01?×?10^-3 mm²/s for differentiating benign from malignant LN with corresponding sensitivity/specificity of 69.70 %/78.57 % and an area under the curve (AUC) of 0.785. The optimal threshold for SUV_mean was 2.5 with corresponding sensitivity/specificity of 69.72 %/90.48 % and with an AUC of 0.832. ADC values and SUV_mean showed a moderate significant inverse correlation (r?=?-0.63).

Conclusion

Both modalities reveal similar moderate diagnostic performance for preoperative lymph node staging of prostate cancer, not justifying their application in routine clinical practice at this time. The only moderate inverse correlation between ADC values and SUV_mean suggests that both imaging parameters might provide complementary information on tumour biology.

Key Points

? Conventional imaging shows low performance for lymph node staging in prostate cancer. ? DWI and 11C-choline PET/CT both provide additional functional information ? Both functional modalities reveal only moderate diagnostic performance.     

In vivo imaging of human breast cancer mouse model with high level expression of calcium sensing receptor at 3T

Objectives

To demonstrate that manganese can visualise calcium sensing receptor (CaSR)-expressing cells in a human breast cancer murine model, as assessed by clinical 3T magnetic resonance (MR).

Methods

Human MDA-MB-231-Luc or MCF7-Luc breast cancer cells were orthotopically grown in NOD/SCID mice to a minimum mass of 5?mm. Mice were evaluated on T1-weighted sequences before and after intravenous injection of MnCl₂. To block the CaSR-activated Ca²⁺ channels, verapamil was injected at the tumour site 5?min before Mn²⁺ administration. CaSR expression in vivo was studied by immunohistochemistry.

Results

Contrast enhancement was observed at the tumour periphery 10?min after Mn²⁺ administration, and further increased up to 40?min. In verapamil-treated mice, no contrast enhancement was observed. CaSR was strongly expressed at the tumour periphery.

Conclusion

Manganese enhanced magnetic resonance imaging can visualise CaSR-expressing breast cancer cells in vivo, opening up possibilities for a new MR contrast agent.

Key Points

? Manganese contrast agents helped demonstrate breast cancer cells in an animal model. ? Enhancement was most marked in cells with high calcium sensing receptor expression. ? Manganese uptake was related to the distribution of CaSR within the tumour. ? Manganese MRI may become useful to investigate human breast cancer.     

In vivo high-resolution magnetic resonance elastography of the uterine corpus and cervix

Objectives

To apply 3D multifrequency MR elastography (3DMMRE) to the uterus and analyse the viscoelasticity of the uterine tissue in healthy volunteers considering individual variations and variations over the menstrual cycle.

Methods

Sixteen healthy volunteers participated in the study, one of whom was examined 12 times over two menstrual cycles. Pelvic 3DMMRE was performed on a 1.5-T scanner with seven vibration frequencies (30–60 Hz) using a piezoelectric driver. Two mechanical parameter maps were obtained corresponding to the magnitude (|G ^* |) and the phase angle (φ) of the complex shear modulus.

Results

On average, the uterine corpus had higher elasticity, but similar viscosity compared with the cervix, reflected by |G ^* |_{uterine corpus}?=?2.58?±?0.52 kPa vs. |G ^* |_cervix?=?2.00?±?0.34 kPa (p?φ _{uterine corpus}?=?0.54?±?0.08, φ _cervix?=?0.57?±?0.12 (p?=?0.428). With 2.23?±?0.26 kPa, |G ^* | of the myometrium was lower in the secretory phase (SP) compared with that of the proliferative phase (PP, |G ^* |?=?3.01?±?0.26 kPa). For the endometrium, the value of |G ^* | in SP was 68 % lower than during PP (PP, |G ^* |?=?3.34?±?0.42 kPa; SP, |G ^* |?=?1.97?±?0.34 kPa; p?=?0.0061).

Conclusion

3DMMRE produces high-resolution mechanical parameter maps of the uterus and cervix and shows sensitivity to structural and functional changes of the endometrium and myometrium during the menstrual cycle.

Key Points

? MR elastography provided for the first time spatially resolved viscoelasticity maps of uterus. ? Uterine corpus had a higher elasticity, but similar viscosity compared with cervix. ? The stiffness of both endometrium and myometrium decreases during the menstrual cycle.