Attenuation correction in pulmonary and myocardial single photon emission computed tomography.

The objective was to develop and validate methods for single photon emission computed tomography, SPECT, allowing quantitative physiological and diagnostic studies of lung and heart. A method for correction of variable attenuation in SPECT, based on transmission measurements before administration of an isotope to the subject, was developed and evaluated. A protocol based upon geometrically well defined phantoms was developed. In a mosaic pattern phantom count rates were corrected from 39-43% to 101-110% of reference. In healthy subjects non-gravitational pulmonary perfusion gradients, observed without attenuation correction were artefacts caused by attenuation. Pulmonary density in centre of right lung, obtained from the transmission measurement, was 0.28 ± 0.03 g ml-1 in normal subjects. Mean density was lower in large lungs compared to smaller ones. We also showed that regional ventilation/perfusion ratios could be measured with SPECT, using the readily available tracer 133Xe. Because of the low energy of 133Xe this relies heavily upon attenuation correction. A commercially available system for attenuation correction with simultaneous emission and transmission, considered to improve myocardial SPECT, performed erroneously. This could lead to clinical misjudgement. We considered that manufacturer-independent pre-clinical tests are required. In a test of two other commercial systems, based on different principles, an adapted variant of our initial protocol was proven useful. Only one the systems provided corrected emission count rates independently on phantom configuration. Errors in the other system were related to inadequate compensation of the influence of emission activity on the transmission study

Platta på mark för Passivhus - Fuktsäkerhet och Värmeisolerande förmåga

The legislation for energy consumption in homes has been strengthened in recent years. In pursuit of energy-efficient homes various forms of low-energy houses have been developed, including Passive Houses. Progress has been made regarding walls, windows and roofs to create a low U-value, while the foundation of the house has been put aside from energy saving point of view. For that reason the aim with this report is to illustrate alternative solutions to slab on grade with good thermal insulation and a minimized thermal bridge. The foundation is an important part of the building that should have good bearing capacity, thermal insulating ability and serve as the building's moisture barrier against the ground. Today we seek to achieve these functions primarily through the following layers of materials, described from the soil and up to floor level. 150 mm of macadam as draining layer and to prevent capillary action EPS foam, normally 300 mm, as thermal insulation and as a complementing preventive layer of capillary action Concrete slab with reinforcement as bearing material Slab edges are often constructed with an L-shaped concrete mould of EPS foam (L-elements), which is practical and good from a strength and moisture-resistant point of view, but they create a substantial thermal bridge along the edges. The thermal bridge increases the total U-value significantly and should be minimized in order to reduce energy consumption during the usage stage of the house. According to the new legislation from 2009 by BBR thermal bridges must now be included in energy calculations. Two foundation constructions, created to provide good thermal insulation and moisture safety, are selected for closer examination; “U-min grund” (passive foundation) from the company Supergrund AB and “Koljerntekniken” from MRD Sälj och Bygg AB. The study of the constructions will be focused on their thermal insulation ability and moisture safety but also with consideration to economy and strength. “U-min grund” is constructed as a traditional Swedish slab on grade with concrete slab and EPS foam insulation under the slab. To achieve a low U-value the layer of EPS foam is 400 mm thick and the slab edges are constructed with U-shaped concrete mould of EPS (U-elements) to break the thermal bridge. The thick thermal insulation creates a large temperature difference between the ground and the surface of the concrete slab. This gives a low relative humidity RH in the upper part of the concrete slab, 53% according to our calculations, which makes the foundation very good from moisture point of view. “Koljerntekniken” is constructed by cellular glass held together with metal profiles to form a 400 mm thick board. Cellular glass should serve both as a bearing and thermal insulating material. Furthermore cellular glass is fully air-and moisture-tight according to the construction company Pittsburgh Corning, which makes the foundation water proof. Both foundation constructions have good results in energy calculations. According to our calculations, with the software HEAT2, the thermal bridge is minimal in “Koljerntekniken” which results in a U-value, including thermal bridges, of 0.089 W/(m2K). “U-min grund” creates a more significant thermal bridge along the edges but has essentially the same U-value of 0.094 W/(m2K). However, through a discussion with Lars Sentler, Professor of Building Construction at Lund University, there are indications that the strength in both “Koljerntekniken” and “U-min grund” is unstable. The weakness is located along the slab edges where the load from the building is led down. A rough disposition of the production cost shows that “U-min grund” is only slightly more expensive than a classic slab on grade with L-elements and 300 mm EPS foam. “Koljerntekniken” however is more than twice as expensive to manufacture, largely because of the production cost of cellular glass. One of the conclusions of this report is that the slab on grade technique used today is not suitable for future Passive Houses. The problem of minimizing the thermal bridge, while maintaining other functions along the edges, turns out to be difficult to solve. The report reveals that more focus must be put on the design of the foundation, to create a well functioning building with low energy consumption and long lifetime

Pre-treatment 18F-choline PET/CT is prognostic for biochemical recurrence, development of bone metastasis, and cancer specific mortality following radical local therapy of high-risk prostate cancer

Abstract Background The aim of this study was to determine whether lymph node metastasis on pre-treatment 18F-choline PET/CT is an independent prognostic factor for biochemical recurrence (BCR), skeletal metastasis, and cancer specific mortality (CSM), after radical local treatment (radical prostatectomy and/or radiotherapy) in men with high-risk prostate cancer. Medical records were reviewed for men with newly diagnosed high-risk prostate cancer who had pre-treatment 18F-choline positron emission tomography fused with computed tomography (PET/CT) scan for primary metastasis staging. Results Of 174 eligible men, 124 met the criteria for inclusion. The PET/CT scan was negative for metastasis in 97 (78%) men, inconclusive in 15 (12%), and positive in 12 (10%). The men with a positive PET/CT scan had significantly shorter time to BCR (p = 0.02), time to skeletal metastasis (p = 0.002), and time to prostate cancer specific death (p < 0.001). On multivariable Cox regression analysis, including also tumour stage, Gleason score, and PSA, a non-negative PET/CT scan was the only significant covariate for time to BCR (HR 2.6, 95% CI 1.3–5.5) and time to skeletal metastasis (HR 2.7, 95% CI 1.3–5.9). Conclusions In men with a newly diagnosed high-risk prostate cancer and a negative or inconclusive bone scan, 18F-choline uptake on PET/CT suggestive metastasis was associated with recurrence, progression to distant metastasis, and prostate cancer death. This strongly indicates that the choline uptakes represented metastasis and not false positive findings

Quantitative SPECT by attenuation correction of the projection set using transmission data: evaluation of a method

A method for measuring attenuation coefficients in single-photon emission tomography (SPECT) is described and evaluated, together with a method for attenuation correction using these measured attenuation coefficients. Build-up, caused by scattered photons, is corrected for by a simple substitution in the algorithms. Transmission studies are performed with a 99mTc- or 57Co flood source, and emission phantom studies with 99mTc line sources. The method is evaluated with variable but well-defined phantoms. The result is accurate attenuation coefficients for different densities, dimensions and geometries, and an accuracy of corrected emission activities of better than +/- 10% in most cases. The present limitations of the method for attenuation correction are discussed

Impact of penalizing factor in a block-sequential regularized expectation maximization reconstruction algorithm for 18F-fluorocholine PET-CT regarding image quality and interpretation

Abstract Background Recently, the block-sequential regularized expectation maximization (BSREM) reconstruction algorithm was commercially introduced (Q.Clear, GE Healthcare, Milwaukee, WI, USA). However, the combination of noise-penalizing factor (β), acquisition time, and administered activity for optimal image quality has not been established for 18F-fluorocholine (FCH). The aim was to compare image quality and diagnostic performance of different reconstruction protocols for patients with prostate cancer being examined with 18F-FCH on a silicon photomultiplier-based PET-CT. Thirteen patients were included, injected with 4 MBq/kg, and images were acquired after 1 h. Images were reconstructed with frame durations of 1.0, 1.5, and 2.0 min using β of 150, 200, 300, 400, 500, and 550. An ordered subset expectation maximization (OSEM) reconstruction with a frame duration of 2.0 min was used for comparison. Images were quantitatively analyzed regarding standardized uptake values (SUV) in metastatic lymph nodes, local background, and muscle to obtain contrast-to-noise ratios (CNR) as well as the noise level in muscle. Images were analyzed regarding image quality and number of metastatic lymph nodes by two nuclear medicine physicians. Results The highest median CNR was found for BSREM with a β of 300 and a frame duration of 2.0 min. The OSEM reconstruction had the lowest median CNR. Both the noise level and lesion SUVmax decreased with increasing β. For a frame duration of 1.5 min, the median quality score was highest for β 400-500, and for a frame duration of 2.0 min the score was highest for β 300-500. There was no statistically significant difference in the number of suspected lymph node metastases between the different image series for one of the physicians, and for the other physician the number of lymph nodes differed only for one combination of image series. Conclusions To achieve acceptable image quality at 4 MBq/kg 18F-FCH, we propose using a β of 400-550 with a frame duration of 1.5 min. The lower β should be used if a high CNR is desired and the higher if a low noise level is important

Impact of acquisition time and penalizing factor in a block-sequential regularized expectation maximization reconstruction algorithm on a Si-photomultiplier-based PET-CT system for 18F-FDG

Background: Block-sequential regularized expectation maximization (BSREM), commercially Q. Clear (GE Healthcare, Milwaukee, WI, USA), is a reconstruction algorithm that allows for a fully convergent iterative reconstruction leading to higher image contrast compared to conventional reconstruction algorithms, while also limiting noise. The noise penalization factor β controls the trade-off between noise level and resolution and can be adjusted by the user. The aim was to evaluate the influence of different β values for different activity time products (ATs = administered activity × acquisition time) in whole-body 18F-fluorodeoxyglucose (FDG) positron emission tomography with computed tomography (PET-CT) regarding quantitative data, interpretation, and quality assessment of the images. Twenty-five patients with known or suspected malignancies, referred for clinical 18F-FDG PET-CT examinations acquired on a silicon photomultiplier PET-CT scanner, were included. The data were reconstructed using BSREM with β values of 100–700 and ATs of 4–16 MBq/kg × min/bed (acquisition times of 1, 1.5, 2, 3, and 4 min/bed). Noise level, lesion SUVmax, and lesion SUVpeak were calculated. Image quality and lesion detectability were assessed by four nuclear medicine physicians for acquisition times of 1.0 and 1.5 min/bed position. Results: The noise level decreased with increasing β values and ATs. Lesion SUVmax varied considerably between different β values and ATs, whereas SUVpeak was more stable. For an AT of 6 (in our case 1.5 min/bed), the best image quality was obtained with a β of 600 and the best lesion detectability with a β of 500. AT of 4 generated poor-quality images and false positive uptakes due to noise. Conclusions: For oncologic whole-body 18F-FDG examinations on a SiPM-based PET-CT, we propose using an AT of 6 (i.e., 4 MBq/kg and 1.5 min/bed) reconstructed with BSREM using a β value of 500–600 in order to ensure image quality and lesion detection rate as well as a high patient throughput. We do not recommend using AT < 6 since the risk of false positive uptakes due to noise increases

[F-18]Fluorodeoxyglucose - positron emission tomography/computed tomography improves staging in patients with high-risk muscle-invasive bladder cancer scheduled for radical cystectomy

Objective. The aim of this study was to evaluate the clinical use of [F-18]-fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) in addition to conventional preoperative radiological investigations in a defined group of patients with high-risk muscle-invasive bladder cancer. Materials and methods. In total, 103 patients with high-risk muscle-invasive bladder cancer defined as stage T3/T4 disease or as stage T2 with hydronephrosis or high-risk histological features, who were provisionally scheduled to undergo cystectomy, were prospectively recruited to the study. The patients were referred to FDG-PET/CT in addition to standard preoperative investigation with computed tomography (CT). The final treatment decision was reached at a multidisciplinary conference based on all available information including the FDG-PET/Cf findings. Results. Compared to CT alone, FDG-PET/CT provided more supplemental findings suggesting malignant manifestations in 48 (47%) of the 103 patients. The additional FDG-PET/CT findings led to an altered provisional treatment plan in 28 out of 103 patients (27%), detection of disseminated bladder cancer and subsequent cancellation of the initially intended cystectomy in 16 patients, and identification of disseminated disease and treatment with induction chemotherapy before radical cystectomy in 12 patients. Conclusions. Preoperative FDG-PET/CT changed the treatment plan for a considerable proportion (27%) of the present patients. Accordingly, such examination can potentially improve the preoperative staging of cystectomy patients with high-risk features, and may also reduce the number of futile operations in patients with advanced disease who are beyond cure

Concordance between four European centres of PET reporting criteria designed for use in multicentre trials in Hodgkin lymphoma

PURPOSE: To determine if PET reporting criteria for the Response Adapted Treatment in Hodgkin Lymphoma (RATHL) trial could enable satisfactory agreement to be reached between 'core' laboratories operating in different countries.METHODS: Four centres reported scans from 50 patients with stage II-IV HL, acquired before and after two cycles of Adriamycin/bleomycin/vinblastine/dacarbazine. A five-point scale was used to score response scans using 'normal' mediastinum and liver as reference levels. Centres read scans independently of each other. The level of agreement between centres was determined assuming (1) that uptake in sites involved at diagnosis that was higher than liver uptake represented disease (conservative reading), and (2) that uptake in sites involved at diagnosis that was higher than mediastinal uptake represented disease (sensitive reading).RESULTS: There was agreement that the response scan was 'positive' or 'negative' for lymphoma in 44 patients with a conservative reading and in 41 patients with a sensitive reading. Kappa was 0.85 (95% CI 0.74-0.96) for conservative reading and 0.79 (95% CI 0.67-0.90) for sensitive reading. Agreement was reached in 46 and 44 patients after discussion for the conservative and sensitive readings, respectively.CONCLUSION: The criteria developed for reporting in the RATHL trial are sufficiently robust to be used in a multicentre setting

PET-CT for staging and early response:results from the Response-Adapted Therapy in Advanced Hodgkin Lymphoma study

International guidelines recommend that positron emission tomography-computed tomography (PET-CT) should replace CT in Hodgkin lymphoma (HL). The aims of this study were to compare PET-CT with CT for staging and measure agreement between expert and local readers, using a 5-point scale (Deauville criteria), to adapt treatment in a clinical trial: Response-Adapted Therapy in Advanced Hodgkin Lymphoma (RATHL). Patients were staged using clinical assessment, CT, and bone marrow biopsy (RATHL stage). PET-CT was performed at baseline (PET0) and after 2 chemotherapy cycles (PET2) in a response-adapted design.PET-CTwasreported centrally by experts at 5 national core laboratories. Local readers optionally scored PET2scans. TheRATHLand PET-CT stages were compared. Agreement among experts and between expert and local readers was measured. RATHL and PET0 stage were concordant in 938 (80%) patients. PET-CT upstaged 159 (14%) and downstaged 74 (6%) patients. Upstaging by extranodal disease in bone marrow (92), lung (11), or multiple sites (12) on PET-CT accounted for most discrepancies. Follow-up of discrepant findings confirmed the PET characterization of lesions in the vast majority. Five patients were upstaged by marrow biopsy and 7 by contrast-enhanced CT in the bowel and/or liver or spleen. PET2 agreement among experts (140 scans) with a k (95% confidence interval) of 0.84 (0.76-0.91) was very good and between experts and local readers (300 scans) at 0.77 (0.68-0.86) was good. These results confirm PET-CT as the modern standard for staging HL and that response assessment using Deauville criteria is robust, enabling translation of RATHL results into clinical practice