Impact of the point spread function on maximum standardized uptake value measurements in patients with pulmonary cancer.

Maximum standardized uptake value (SUVmax) from fluorodeoxyglucose (FDG) positron emission tomography (PET) scans is a semi quantitative measure that is increasingly used in the clinical practice for diagnostic and therapeutic response assessment purposes. Technological advances such as the implementation of the point spread function (PSF) in the reconstruction algorithm have led to higher signal to noise ratio and increased spatial resolution. The impact on SUVmax measurements has not been studied in clinical setting. We studied the impact of PSF on SUVmax in 30 consecutive lung cancer patients. SUVmax values were measured on PET-computed tomography (CT) scans reconstructed iteratively with and without PSF (respectively high-definition [HD] and non-HD). HD SUVmax values were significantly higher than non-HD SUVmax. There was excellent correlation between HD and non-HD values. Details of reconstruction and PSF implementation in particular have important consequences on SUV values. Nuclear Medicine physicians and radiologists should be aware of the reconstruction parameters of PET-CT scans when they report or rely on SUV measurements.

Evaluation of FLT-PET-CT as an imaging biomarker of proliferation in primary breast cancer.

BACKGROUND: [(18)F]fluorothymidine (FLT) has been proposed as a positron emission tomography (PET)-imaging biomarker of proliferation for breast cancer. The aim of this prospective study was to assess the feasibility of FLT-PET-CT as a technique for predicting the response to neoadjuvant chemotherapy (NAC) in primary breast cancer and to compare baseline FLT with Ki-67. METHODS: Twenty women with primary breast cancer had a baseline FLT-PET-CT scan that was repeated before the second cycle of chemotherapy. Expression of Ki-67 in the diagnostic biopsy was quantified. From the FLT-PET-CT scans lesion maximum and mean standardised uptake values (SUVmax, SUVmean) were calculated. RESULTS: Mean baseline SUVmax was 7.3, and 4.62 post one cycle of NAC, representing a drop of 2.68 (36.3%). There was no significant association between baseline, post chemotherapy, or change in SUVmax and pathological response to NAC. There was a significant correlation between pre-chemotherapy Ki-67 and SUVmax of 0.604 (P=0.006). CONCLUSIONS: Baseline SUVmax measurements of FLT-PET-CT were significantly related to Ki-67 suggesting that it is a proliferation biomarker. However, in this series neither the baseline value nor the change in SUVmax after one cycle of NAC were able to predict response as most patients had a sizeable SUVmax reduction.

Can combined 18F-FDG-PET and dynamic contrast-enhanced MRI predict behavior of desmoid tumors in patients with familial adenomatous polyposis?

BACKGROUND: Desmoid tumors associated with familial adenomatous polyposis show variable behavior; about 10% grow relentlessly, resulting in severe morbidity or mortality. Investigations that could identify the minority of desmoid tumors that behave aggressively would allow these tumors to be treated early and spare the majority of patients who have more benign disease from unnecessary intervention. OBJECTIVE: The aim of this study was to investigate whether imaging the tumor metabolic-vascular phenotype by modern methods predicts growth. DESIGN: This is a prospective case series study. SETTINGS: The study was conducted at a tertiary center specializing in familial adenomatous polyposis and desmoid disease. PATIENTS: Nine patients with familial adenomatous polyposis (4 male, mean age 39 years) with desmoid tumor underwent 18F-FDG-PET and dynamic contrast-enhanced MRI. Standard MRI was repeated a year later to assess tumor growth. MAIN OUTCOME MEASURES: The primary outcome measured was the correlation between 18F-FDG-PET and dynamic contrast-enhanced MRI parameters and subsequent desmoid growth. RESULTS: Failed intravenous access precluded dynamic contrast-enhanced MRI in 1 female patient. Thirteen desmoid tumors (4 intra-abdominal, 2 extra-abdominal, 7 abdominal wall; mean area, 68 cm) were analyzed in the remaining 8 patients. Two patients died before follow-up MRI. Five tumors decreased in size, 3 increased in size, and 3 remained stable after a year. Significant correlation (Spearman rank correlation, significance at 5%) existed between maximum standardized uptake value and k(ep) (r = -0.56, p = 0.04), but not with other vascular parameters (K(trans) (r = -0.47, p = 0.09); v(e) (r = -0.11, p = 0.72); integrated area under the gadolinium-time curve at 60 seconds (r = -0.47, p = 0.10)). There was no significant difference in the maximum standardized uptake value or dynamic contrast-enhanced MRI parameters (K(trans), v(e), k(ep), integrated area under the gadolinium-time curve at 60 seconds) between the tumors that grew or decreased in size or between the tumor sites. However, vascular metabolic ratio (maximum standardized uptake value/K(trans)) was significantly different for tumor site (p = 0.001) and size (p = 0.001, 1-way ANOVA). LIMITATIONS: This investigation is limited because of its exploratory nature and small patient numbers. CONCLUSIONS: Although not predictive for tumor behavior, some correlations existed between dynamic contrast-enhanced MRI and 18F-FDG-PET parameters. Vascular metabolic ratio may provide further information on tumor behavior; however, this needs to be evaluated with further larger studies.

Investigation of dose minimisation protocol for 18F-FDG PET-CT in the management of lymphoma postchemotherapy followup.

INTRODUCTION: (18)F-FDG-PET-CT plays an important role in the management of lymphoma postchemotherapy followup. Some centres perform prechemotherapy baseline CT and postchemotherapy PETCT. With a concern of radiation burden, especially in young patients, this study aimed to assess if PETCT radiation dose could be reduced. METHODS: Retrospective analysis of 100 lymphoma patients was performed to record sites of disease on prechemotherapy CT and postchemotherapy PETCT. The potential reduction in radiation and time achieved with PETCT limited to sites of known disease identified on prechemotherapy CT was calculated. RESULTS: No FDG-uptake was seen in 72 cases. FDG uptake at known disease sites was seen in 24. Of the remaining 4, one had clinically significant pathology, a rectal adenocarcinoma. PETCT did not reveal any unexpected sites of lymphoma. Limiting PETCT to sites of known disease would have saved a mean radiation dose of 4 mSv (27.3%), with a mean time of 16 minutes. CONCLUSION: Our study suggests that young patients may benefit from reduced radiation by limiting PETCT to sites of known disease with low risk of missing significant pathology. However, in older patients, with increased incidence of asymptomatic synchronous malignancies, whole-body PETCT is advisable unless prechemotherapy PETCT has been performed.

Age and dose-limited PET-CT scan regime in lymphoma: between the devil and the deep blue sea?

In this study the authors speculate about hypothetical effective-dose (E) reduction through limiting post-chemotherapy PET-CT scanning to lymphoma sites previously identified on pre-treatment CT. E reductions/scan time savings are compared between post-treatment standard and theoretically limited PET-CT scans. The influence of patient age with E savings and associated clinical implication for 100 subjects are discussed. The greatest E theoretical savings of 52 and 32% for the CT contribution and combined PET-CT, respectively, were seen in patients <18 y old using limited scans in this study, with a potential mean time saving of 16 min per patient across the entire cohort. However, the limited PET-CT regime here missed a 1% rate of unexpected cancer that standard PET-CT recorded. The authors recommend performing larger scale multi-centre studies comparing PET-CT pre- and post-chemotherapy to establish full clinical efficacy of this method.

Adaptive 18fluoro-2-deoxyglucose positron emission tomography/computed tomography-based target volume delineation in radiotherapy planning of head and neck cancer.

AIMS: This study investigated an adaptive threshold-based method to delineate the target volume using (18)fluoro-2-deoxyglucose ((18)FDG) positron emission tomography/computed tomography (PET/CT) before and during a course of radical radiotherapy or chemoradiotherapy in locally advanced squamous cell carcinoma of the head and neck. MATERIALS AND METHODS: Ten patients were enrolled between March 2006 and May 2008. (18)FDG PET/CT scans were carried out 72h before the start of radiotherapy and then at three time points during radiotherapy (8-18, 36-50 and 66Gy). Functional volumes were delineated using an adaptive iterative algorithm weighted according to the mean standard uptake value (SUV(mean)) within the region of interest. The background (18)FDG uptake, maximum standard uptake value (SUV(max)) and SUV(mean) within the volumes were assessed. RESULTS: There was no significant reduction in the primary target volumes defined by the adaptive threshold during radiotherapy. However, the SUV(max) significantly reduced within the primary (P=0.003-0.011) and lymph node (P<0.0001) target volume at 36-50 and 36-66Gy compared with 0Gy. The SUV(mean) was negatively correlated to radiation dose (P<0.0001-0.014). The ratio between the background uptake of (18)FDG and the SUV(mean) significantly reduced for both the lymph node target volume at 36-50Gy and the primary volume at 66Gy. The lack of significant correlation between the defined volume and radiation dose was because the SUV(mean) within the region of interest used to define the edge of the volume was equal to or less than the background (18)FDG uptake and the software was unable to effectively differentiate between tumour and background uptake. CONCLUSIONS: The adaptive threshold method may be of benefit when used to define the target volume before the start of radiotherapy. This method was not beneficial during radiotherapy because the software is not sensitive enough to distinguish tumour from background and define a volume. (18)FDG PET/CT-guided volumes delineated by automatic adaptive thresholding methods should only be used for dose escalation with the pretreatment imaging.

Combined MR imaging and numerical simulation of flow in realistic arterial bypass graft models.

We report methods for (a) transforming a three-dimensional geometry acquired by magnetic resonance angiography (MRA) in vivo, or by imaging a model cast, into a computational surface representation, (b) use of this to construct a three dimensional numerical grid for computational fluid dynamic (CFD) studies, and (c) use of the surface representation to produce a stereo-lithographic replica of the real detailed geometry, at a scale convenient for detailed magnetic resonance imaging (MRI) flow studies. This is applied to assess the local flow field in realistic geometry arterial bypass grafts. Results from a parallel numerical simulation and MRI measurement of flow in an aorto-coronary bypass graft with various inlet flow conditions demonstrate the strong influence of the graft inlet waveform on the perianastomotic flow field. A sinusoidal and a multi harmonic coronary flow waveform both with a mean Reynolds number (Re) of 100 and a Womersley parameter of 2.7 were applied at the graft inlet. A weak axial flow separation region just distal to the toe was found in sinusoidal flow near end deceleration (Re = 25). At the same location and approximately the same point in the cycle (Re = 30) but in coronary flow, the axial flow separation was stronger and more spatially pronounced. No axial flow separation occurred in steady flow for Re = 100. Numerical predictions indicate a region in the vicinity of the suture line (where there is a local narrowing of the graft) with a wall shear magnitude in excess of five times that associated with fully developed flow at the graft inlet.

Preliminary study of potential for rapid prototype and surface scanned radiotherapy facemask production technique.

Preliminary investigations into the potential of an elegant technique to create a rudimentary facemask for patient immobilization during radiotherapy treatment are presented. This method combines modern technology to cause the patientfar less discomfort compared with current plaster of Paris (POP) face mould procedures. Near instantaneous patient face scanning is accomplished with charge-coupled devices for imaging in an optical surface scanning system. The surface generated data is input to a rapid prototype (RP) system that creates a life-size model of the patient's face topology. As proof of principle a basic prototype facemask was successfully constructed using this technique and some qualitative comparison measurements for position and surface dose were made. These initial results confirm the validity of this technique and justify the need for further quantitative studies to fully investigate the potential of RP facemasks over POP based methods for mask production.