Respiratory motion during 90Yttrium PET contributes to underestimation of tumor dose and overestimation of normal liver tissue dose.

Background Yttrium-90 dosimetry after radioembolization is reliant on accurate quantitative imaging of the microsphere deposition. Previous studies have focused on the correction of geometrical resolution effects. Purpose To uncover additional effects of respiratory motion. Material and Methods Mathematical models describing spherical tumors were formed and two blurring effects, limited geometrical resolution and respiratory motion, were simulated. The virtual images were used as basis for dose volume histogram estimations by convolving the radioactivity representations with a dose point kernel. Results For respiratory motion only, the largest errors were found for the smallest tumors and/or tumors with heterogeneous distribution of yttrium-90 microspheres. The deviations in max dose and dose to 25% and 50% of the tumor volume were estimated at 20-40%, 10-30%, and 0-30%, respectively. Additional blurring from geometrical resolution increased the errors to 55-75%, 50-60%, and 25-60%, respectively. Conclusion Respiratory motion contributes to underestimation of tumor dose and overestimation of normal tissue dose.

Respiratory gated and prolonged acquisition 18F-FDG PET improve preoperative assessment of colorectal liver metastases.

BACKGROUND: Detection of small liver metastases from colorectal cancer by 18F-FDG PET/CT is hampered by high physiologic uptake in the liver parenchyma and respiratory movements during image acquisition. PURPOSE: To investigate whether two tailored 18F-FDG PET liver acquisitions (prolonged liver acquisition time [PL-PET] and repeated breath-hold respiratory gated liver acquisition [RGL-PET]) would improve detection of colorectal liver metastases, when added to a standard whole body PET (WB-PET). MATERIAL AND METHODS: Twenty consecutive patients referred to our hospital for surgical treatment of colorectal liver metastases diagnosed with contrast-enhanced CT underwent preoperative 18F-FDG PET/CT tailored for detection of liver metastases. Concordance between preoperative imaging results and true findings (histology and/or follow-up imaging) as well as changes in clinical management, based on 18F-FDG PET/CT findings, were documented. Background noise, defined as the standard deviation measured in a reference region within the normal liver parenchyma, was compared between the three 18F-FDG PET/CT protocols. RESULTS: WB-PET, PL-PET, and RGL-PET showed suspicious liver lesions in 18 out of 20 patients. Compared to WB-PET alone, the combination of PL-PET and RGL-PET showed additional lesions in the liver in seven out of the 18 patients. The combination of all three PET acquisitions changed clinical management in four patients. Two patients with negative PET results were later found to have benign liver lesions. CONCLUSION: The addition of tailored liver-specific 18F-FDG PET/CT protocols (PL-PET and RGL-PET) to a WB-PET, improved the detection of intrahepatic colorectal metastases, compared to WB-PET alone. Such add-ons can change clinical patient management of potentially resectable colorectal liver metastases.

Characterization of an asymmetric add-on collimator used with a hand-held gamma probe for radioguided surgery and sentinel node detection: a demonstration of an alternative collimation method.

OBJECTIVE: The aim of the study was to investigate a new principle for collimation of gamma probes for radioguided surgery and sentinel node detection: the use of asymmetric lateral shielding. The intension was to maintain the sensitivity in the lateral and forward directions on the unshielded side while at the same time to shield the probe against high activity sources that could mask the signal from the object to be detected. METHODS: The device was constructed to shield only against photons that come from a region in space that spans approximately 180° sideways and forwards relative to the detector. The intension of the study was to demonstrate the principle rather than to document its use in the clinic. Sensitivity profiles were derived from measurements obtained while stepwise moving the probe relatively to a point source of known activity surrounded by water. The measurements were taken in the symmetry plane of the collimator where the shielding effects were expected to be most pronounced. RESULTS: The asymmetric collimator led to nearly unchanged sensitivity in the lateral and forward directions. At the same time, the field of view was effectively shrunk on the shielded side. Contributions from sources lateral and close to the shield were reduced by factors up to 45. CONCLUSION: By rotating the probe around its longitudinal axis, an asymmetric add-on shield collimator could potentially make it easier to detect a sentinel node when this is located close to a neighbouring high activity region like the urinary bladder or the injection site.

An implementation of time-efficient respiratory-gated PET acquisition by repeated breath-holds.

BACKGROUND: Respiratory gating in positron emission tomography (PET) is used to improve detection of small tumors in the lower lung regions and in the liver, and to obtain a better estimate of the standardized uptake value (SUV). PURPOSE: To develop a time-efficient method for acquisition of respiratory-gated PET/CT that would produce one single high quality image volume corresponding to a breath-hold state. MATERIAL AND METHODS: An instrument was developed that displayed to the patient either red or green numbers, counting down from a chosen maximum to one at a rate of one dial per second. The patient was instructed to repeatedly hold the breath in moderate inspiration when red numbers were displayed and to breathe freely during display of green numbers. PET data were acquired in list mode and trigger signals were sent to the scanner and inserted into the list file each time the color of the countdown numbers switched from green to red. Data acquired during breath-holds were used to create one single image volume. RESULTS: High quality breath-hold images were obtained from 10 min data acquisition at one bed position. Improved image quality compared to standard whole-body PET was demonstrated by a significant reduction of noise (standard deviation) in regions of normal liver tissues. CONCLUSION: The instruction to perform repeated breath-holds was well understood by patients and they cooperated satisfactorily. When the new procedure is used the duration of the data acquisition may typically be reduced by a factor of 4 compared to conventional respiratory-gated protocols where the patient breathes freely.

Correction of partial volume effect in (18)F-FDG PET brain studies using coregistered MR volumes: voxel based analysis of tracer uptake in the white matter.

A voxel-based algorithm to correct for partial volume effect in PET brain volumes is presented. This method (named LoReAn) is based on MRI based segmentation of anatomical regions and accurate measurements of the effective point spread function of the PET imaging process. The objective is to correct for the spill-out of activity from high-uptake anatomical structures (e.g. grey matter) into low-uptake anatomical structures (e.g. white matter) in order to quantify physiological uptake in the white matter. The new algorithm is presented and validated against the state of the art region-based geometric transfer matrix (GTM) method with synthetic and clinical data. Using synthetic data, both bias and coefficient of variation were improved in the white matter region using LoReAn compared to GTM. An increased number of anatomical regions doesn't affect the bias (<5%) and misregistration affects equally LoReAn and GTM algorithms. The LoReAn algorithm appears to be a simple and promising voxel-based algorithm for studying metabolism in white matter regions.

A gel tumour phantom for assessment of the accuracy of manual and automatic delineation of gross tumour volume from FDG-PET/CT.

INTRODUCTION: Our primary aim was to make a phantom for PET that could mimic a highly irregular tumour and provide true tumour contours. The secondary aim was to use the phantom to assess the accuracy of different methods for delineation of tumour volume from the PET images. MATERIAL AND METHODS: An empty mould was produced on the basis of a contrast enhanced computed tomography (CT) study of a patient with a squamous cell carcinoma in the head and neck region. The mould was filled with a homogeneous fast-settling gel that contained both (18)F for positron emission tomography (PET) and an iodine contrast agent. This phantom (mould and gel) was scanned on a PET/CT scanner. A series of reference tumour contours were obtained from the CT images in the PET/CT. Tumour delineation based on the PET images was achieved manually, by isoSUV thresholding, and by a recently developed three-dimensional (3D) Difference of Gaussians algorithm (DoG). Average distances between the PET-derived and reference contours were assessed by a 3D distance transform. RESULTS: The manual, thresholding and DoG delineation methods resulted in volumes that were 146%, 86% and 100% of the reference volume, respectively, and average distance deviations from the reference surface were 1.57 mm, 1.48 mm and 1.0, mm, respectively. DISCUSSION: Manual drawing as well as isoSUV determination of tumour contours in geometrically irregular tumours may be unreliable. The DoG method may contribute to more correct delineation of the tumour. Although the present phantom had a homogeneous distribution of activity, it may also provide useful knowledge in the case of inhomogeneous activity distributions. CONCLUSION: The geometric irregular tumour phantom with its inherent reference contours was an important tool for testing of different delineation methods and for teaching delineation.

Quantitative dynamic ¹8FDG-PET and tracer kinetic analysis of soft tissue sarcomas.

PURPOSE: To study soft tissue sarcomas using dynamic positron emission tomography (PET) with the glucose analog tracer [(18)F]fluoro-2-deoxy-D-glucose ((18)FDG), to investigate correlations between derived PET image parameters and clinical characteristics, and to discuss implications of dynamic PET acquisition (D-PET). MATERIAL AND METHODS: D-PET images of 11 patients with soft tissue sarcomas were analyzed voxel-by-voxel using a compartment tracer kinetic model providing estimates of transfer rates between the vascular, non-metabolized, and metabolized compartments. Furthermore, standard uptake values (SUVs) in the early (2 min p.i.; SUVE) and late (45 min p.i.; SUVL) phases of the PET acquisition were obtained. The derived transfer rates K1, k2 and k3, along with the metabolic rate of (18)FDG (MRFDG) and the vascular fraction νp, was fused with the computed tomography (CT) images for visual interpretation. Correlations between D-PET imaging parameters and clinical parameters, i.e. tumor size, grade and clinical status, were calculated with a significance level of 0.05. RESULTS: The temporal uptake pattern of (18)FDG in the tumor varied considerably from patient to patient. SUVE peak was higher than SUVL peak for four patients. The images of the rate constants showed a systematic pattern, often with elevated intensity in the tumors compared to surrounding tissue. Significant correlations were found between SUVE/L and some of the rate parameters. CONCLUSIONS: Dynamic (18)FDG-PET may provide additional valuable information on soft tissue sarcomas not obtainable from conventional (18)FDG-PET. The prognostic role of dynamic imaging should be investigated.

Dynamic FDG PET for assessing early effects of cerebral hypoxia and resuscitation in new-born pigs.

PURPOSE: Changes in cerebral glucose metabolism may be an early prognostic indicator of perinatal hypoxic-ischaemic injury. In this study dynamic ¹8F-FDG PET was used to evaluate cerebral glucose metabolism in piglets after global perinatal hypoxia and the impact of the resuscitation strategy using room air or hyperoxia. METHODS: New-born piglets (n = 16) underwent 60 min of global hypoxia followed by 30 min of resuscitation with a fraction of inspired oxygen (FiO2) of 0.21 or 1.0. Dynamic FDG PET, using a microPET system, was performed at baseline and repeated at the end of resuscitation under stabilized haemodynamic conditions. MRI at 3 T was performed for anatomic correlation. Global and regional cerebral metabolic rates of glucose (CMRgl) were assessed by Patlak analysis for the two time-points and resuscitation groups. RESULTS: Global hypoxia was found to cause an immediate decrease in cerebral glucose metabolism from a baseline level (mean ± SD) of 21.2 ± 7.9 to 12.6 ± 4.7 µmol/min/ 100 g (p <0.01). The basal ganglia, cerebellum and cortex showed the greatest decrease in CMRgl but no significant differences in global or regional CMRgl between the resuscitation groups were found. CONCLUSION: Dynamic FDG PET detected decreased cerebral glucose metabolism early after perinatal hypoxia in piglets. The decrease in CMRgl may indicate early changes of mild cerebral hypoxia-ischaemia. No significant effect of hyperoxic resuscitation on the degree of hypometabolism was found in this early phase after hypoxia. Cerebral FDG PET can provide new insights into mechanisms of perinatal hypoxic- ischaemic injury where early detection plays an important role in instituting therapy.

Nasal deposition and clearance in man: comparison of a bidirectional powder device and a traditional liquid spray pump.

BACKGROUND: Delivery of powder formulations to the nose is an attractive alternative for many drugs and vaccines. This study compared the regional nasal deposition and clearance patterns of lactose powder delivered by the OptiNose powder device (Opt-Powder; OptiNose US Inc., Yardley, PA, USA) to that of liquid aerosol administered via a traditional hand-actuated liquid spray pump (Rexam SP270, Rexam Pharma, France). METHODS: The study was an open-label, crossover design in seven healthy subjects (five females, two males). The regional nasal deposition and clearance patterns of the Opt-Powder device were compared to a traditional liquid spray pump by dynamic gamma camera imaging after administration of either (99m)Tc-labeled lactose powder or liquid (99m)Tc- diethelyne triamine pentaacetic acid-aerosol. The gamma camera images were scaled and aligned with sagittal magnetic resonance images to identify nasal regions. Possible deposition of radiolabeled material in the lungs following both methods of delivery was also evaluated. RESULTS: Both powder and spray were distributed to all of the nasal regions. The Opt-Powder device, however, achieved significantly larger initial deposition in the upper and middle posterior regions of the nose than spray (upper posterior region; Opt-Powder 18.3% ± 11.5 vs. Spray 2.4% ± 1.8, p<0.02; sum of upper and middle posterior regions; Opt-Powder 53.5% ± 18.5 vs. Spray 15.7% ± 13.8, p<0.02). The summed initial deposition to the lower anterior and posterior regions for spray was three times higher compared to Opt-Powder (Opt-Powder 17.4% ± 24.5 vs. Spray 59.4% ± 18.2, p<0.04). OptiNose powder delivery resulted in more rapid overall nasal clearance. No lung deposition was observed. CONCLUSIONS: The initial deposition following powder delivery was significantly larger in the ciliated mucosa of the upper and posterior nasal regions, whereas less was deposited in the lower regions. Overall nasal clearance of powder was slower initially, but due to retention in anterior nonciliated regions the overall nasal clearance after spray was slower.

Dynamic respiratory gated (18)FDG-PET of lung tumors - a feasibility study.

BACKGROUND: (18)FDG-PET/CT imaging is well established for diagnosis and staging of lung tumors. However, more detailed information regarding the distribution of FDG within the tumor, also as a function of time after injection may be relevant. In this study we explore the feasibility of a combined dynamic and respiratory gated (DR) PET protocol. MATERIAL AND METHODS: A DR FDG-PET protocol for a Siemens Biograph 16 PET/CT scanner was set up, allowing data acquisition from the time of FDG injection. Breath-hold (BH) respiratory gating was performed at four intervals over a total acquisition time of 50 minutes. Thus, the PET protocol provides both motion-free images and a spatiotemporal characterization of the glucose distribution in lung tumors. Software tools were developed in-house for tentative tumor segmentation and for extracting standard uptake values (SUVs) voxel by voxel, tumor volumes and SUV gradients in all directions. RESULTS: Four pilot patients have been investigated with the DR PET protocol. The procedure was well tolerated by the patients. The BH images appeared sharper, and SUV(max)/SUV(mean) was higher, compared to free breathing (FB) images. Also, SUV gradients in the periphery of the tumor in the BH images were in general greater than or equal to the gradients in the FB PET images. CONCLUSION: The DR FDG-PET protocol is feasible and the BH images have a superior quality compared to the FB images. The protocol may also provide information of relevance for radiotherapy planning and follow-up. A patient trial is needed for assessing the clinical value of the imaging protocol.

Monitoring the effect of targeted therapies in a gastrointestinal stromal tumor xenograft using a clinical PET/CT.

PURPOSE: The purpose of this study is to assess treatment responses induced by the two tyrosine kinase inhibitors, Imatinib and Sunitinib, in a gastrointestinal stromal tumor (GIST) xenograft using a clinical positron emission tomography/computed tomography (PET/CT) scanner. METHODS: Nude mice bearing human GIST xenografts with mutations in exons 11 and 17 were randomly allocated to treatment with Imatinib, Sunitinib, or placebo daily for seven consecutive days. 2-deoxy-2-[(18)F]fluoro-D: -glucose PET ((18)F-FDG-PET/CT) was performed in a clinical PET/CT scanner at baseline (day 0) and 1 and 7 days after onset of treatment. Treatment response was assessed by measuring tumor volumes and by calculation of tumor-to-liver (18)F-FDG uptake ratios. RESULTS: Minor reductions in tumor volume were observed in both treatment groups. For the two treatment groups, significantly decreased tumor-to-liver uptake ratios were observed both at day 1 (Imatinib, -41%, p = .002; Sunitinib, -55%, p < .001) and at day 8 (Imatinib, -35%, p < .001; Sunitinib, -50%, p < .001), when compared to individual baseline values. For the control tumors, neither tumor volumes nor tumor-to-liver uptake ratios were altered during the 8 days the experiment lasted. CONCLUSIONS: Significant anti-tumor effects were demonstrated following treatment with both Imatinib and Sunitinib. Decreased tumor-to-liver uptake ratios were more pronounced than tumor volume reductions. Effects of novel targeted therapies can be evaluated in the GIST xenograft model using a clinical PET/CT scanner.

A method for on-site measurements of the effective spatial resolution in PET image volumes reconstructed with OSEM and Gaussian post-filters.

When PET image volumes are reconstructed with ordered subset expectation-maximization (OSEM) and subjected to filtration with a 3D Gaussian filter the effective spatial resolution is a function of both the intrinsic scanner resolution and the user-selectable spatial width of the filter. A method was developed to derive the effective spatial resolution from such volumes obtained after acquisitions with a line source on a Siemens Biograph 64 PET/CT scanner. Assuming Gaussian distributions, the full widths at half maximum (FWHM) were derived from probit plots of cumulative spatial distributions across the line source. The effective FWHM values were also used to estimate the FWHM of the intrinsic resolution by extrapolation to a zero filter width.

A new method for scintigraphic quantification of deposition and clearance in anatomical regions of the human nose.

OBJECTIVES: To develop methods for absolute quantification of the deposition of 99mTc-labeled aerosols and powders in well-defined anatomical regions of the nose, and to enable accurate comparisons of different nasal administration techniques in the same individual. METHODS: The volunteer was seated and positioned relative to the scintillation camera field of view by means of a fixation frame. After nasal administration, a dynamic series of images was acquired for 32 min with a lateral direction of view. The images were corrected for photon attenuation by the use of a lateral transmission image acquired before the delivery of aerosols or powders. Marker images, obtained with a line source fixed to a balloon and kept for a short while against the palate as well as with a point source held on anatomical landmarks, were used to co-register the scintigraphic images to sagital sections through a three-dimensional magnetic resonance (MR)-image series. The MR set was used to define the inner nose contour and the nasal regions used for quantification. RESULT: Attenuation correction factors ranged from 1.1 to 1.7 in different parts of the nasal cavity. Alignment of the markers on the teeth and palate with the sagital MR images could be reproduced with accuracies of 1.2 and 1.7 mm, respectively. CONCLUSION: The new method provides reliable quantification of the deposition in anatomic regions that can be defined in MR images. Accurate co-registration and quantification are essential when comparing distribution and clearance patterns for different administration techniques.

A simulation of MRI based dose calculations on the basis of radiotherapy planning CT images.

BACKGROUND: The advantage of MRI-based radiotherapy planning is the superior soft tissue differentiation. However, for accurate patient dose calculations, a conversion of the MR images into Hounsfield CT maps is necessary. The aim of the present study was to investigate the dose accuracy that can be achieved with segmented MR-images derived from the planning CT images by assigning fixed densities to different classes of tissues. METHODS: Treatment plans for ten prostate cancer patients were selected. A collapsed cone algorithm was used to calculate patient dose distributions. The dose calculations were based on four different image sets: (1) the original CT-series (DD(DP)), (2) a simulated MR series with all tissue set to a homogenous water equivalent material of density 1.02 g/cm(3) (DD(W)), (3) a simulated MR series with soft tissue set to a water equivalent material with density 1.02 g/cm(3) and the bone set to a density of 1.3 g/cm(3) (DD(W+B1.3)), and (4) a simulated MR series identical to (3) but with a bone density equal to 2.1 g/cm(3) (DD(W+B2.1)). The dose distributions were compared by analysing dose difference histograms as well as through a visual display of spatial dose deviations. RESULTS: The population based minimum, mean and maximum dose difference between the DD(DP) and DD(W) in the target volume was -2.8, -1.0 and 0.6%, respectively. Corresponding differences between DD(DP) and DD(W+B1.3) were -1.6, 0.2 and 1.5%, respectively, and between DD(DP) and DD(W+B2.1) -4.3, 4.2 and 9.7%, respectively. For the rectum, the differences between CT(DP) and the other image sets were in the range of -19.5 to 8.8%. For the bladder, the differences were in the range of -9.6 to 7.0%. CONCLUSIONS: A systematic study using segmented MR images was undertaken. To achieve an acceptable accuracy in the CTV dose, the MR images should be segmented into bone and water equivalent tissue. Still, significant dose deviation for the organs at risk may be present. As tissue segmentation in real MR images is introduced, segmentation errors and errors that stem from geometrical non-linearities may further reduce the accuracy.

Integrin scintimammography using a dedicated breast imaging, solid-state gamma-camera and (99m)Tc-labelled NC100692.

OBJECTIVE: Integrin scintimammography with NC100692 and a dedicated gamma-camera, LumaGEM, based on semi-conductor technology, was performed to investigate the detection ability of this combination in breast cancer. METHODS: Eight patients with a high suspicion of breast cancer were administered 600-750 MBq (99m)Tc-labelled NC100629. Two acquisitions using a cranio-caudal and a lateral view were used, with moderate compression of the breast. RESULTS: LumaGEM scintigraphy revealed 9 of 11 malignancies, sized 6-20 mm. Two lesions in patients with multicentric disease were not diagnosed, one of which measured only 2.5 mm. In one patient, the procedure was inconclusive, due to major breast hypertrophy. CONCLUSION: The combined use of NC100629 and a dedicated gamma-camera for breast imaging was highly effective in diagnosing breast cancer.

Early changes in apparent diffusion coefficient predict the quantitative antitumoral activity of capecitabine, oxaliplatin, and irradiation in HT29 xenografts in athymic nude mice.

PURPOSE: The purpose of this study was to evaluate the possible use of changes in apparent diffusion coefficient (ADC) measured by magnetic resonance imaging for pretreatment prediction and early detection of tumor response in a mouse model during fractionated chemoradiotherapy. MATERIALS AND METHODS: Athymic mice with bilateral HT29 xenografts on rear flanks were allocated into three groups: control, capecitabine, and capecitabine and oxaliplatin. The left flanks of the mice received daily irradiation. T2 and diffusion images were acquired before therapy and weekly for the following 9 weeks. Pretreatment and changes in ADC were calculated and compared with tumor doubling growth delay. RESULTS: No correlations between pretreatment ADC and changes in tumor volumes after therapy were seen. All treated tumors, except those receiving capecitabine (P = .06), showed increased mean tumor ADC values 11 days after initialization of therapy (P < .05) before returning to pretreatment values within 5 days posttherapy (day 18 after onset of therapy). This increase in mean tumor ADC showed a strong positive correlation (r = 0.92, P < .01) with mean tumor doubling growth delay. CONCLUSIONS: Pretreatment ADC values did not predict the effectiveness of therapy, whereas early changes in mean ADC quantitatively correlated with treatment outcome.

Breath actuated device improves delivery to target sites beyond the nasal valve.

OBJECTIVES: The objective was to compare nasal deposition patterns achieved with a conventional hand actuated spray pump and a novel breath actuated bidirectional prototype device housing the same spray pump (OptiMist, OptiNose AS, Oslo, Norway). STUDY DESIGN AND METHODS: The bidirectional delivery device exploits the posterior connection between the nasal passages persisting when the velum automatically closes during oral exhalation. The deposition and clearance patterns achieved with the two devices were compared in nine healthy subjects by scintigraphy after administration of Tc-aerosols. RESULTS: Compared with traditional spray pump delivery, the OptiMist device provided significantly (P < .004) larger initial and cumulative deposition (area under the deposition vs. time curve) in the upper posterior segment of the nasal passage, housing the sinus ostia and the olfactory region, and significantly lower deposition (P < .004) in the anterior segment, lined by nonciliated squamous epithelium. Furthermore, intersubject reproducibility of the initial and cumulative deposition was higher for the OptiMist device both in the upper posterior segment and the entire nose. CONCLUSIONS: Compared with a spray pump, the novel breath actuated bidirectional device provides significantly larger deposition in the clinically important regions beyond the nasal valve and reduced anterior deposition. These striking differences provide new opportunities for improved therapy of chronic rhinosinusitis and polyposis as well as extended use of the nose for delivery of drugs from the nose into the brain.

Localized internal radiotherapy with 90Y particles embedded in a new thermosetting alginate gel: a feasibility study in pigs.

BACKGROUND: Internal radiotherapy requires the localization of the radionuclide to the site of action. A new injectable alginate gel formulation intended to undergo immediate gelation in tissues and capable of encapsulating radioactive particles containing 90Y was investigated. METHODS: The formulation was injected intramuscularly, into the bone marrow compartment of the femur and intravenously, respectively, in pigs. The distribution of radioactivity in various tissues was determined. RESULTS: Following intramuscular injection, more than 90% of the radioactivity was found at the site of injection. Following injection into bone marrow, 30-40% of the radioactivity was retained at the site of injection, but a considerable amount of radioactivity was also detected in the lungs (35-45%) and the liver (5-18%). Following intravenous injection, 80-90% of the radioactivity was found in the lungs. CONCLUSION: The present formulation appears suitable for localized radiotherapy in organs and tissues having low perfusion.

Effects of photon attenuation on the determination of cardiac volumes from reconstructed counts in gated blood pool SPET.

In gated cardiac blood pool single-photon emission tomography (SPET), the volume of a ventricle may be determined by a method that exploits the proportionality between that volume and the total reconstructed counts within a larger volume of interest that includes the actual ventricle. The present work was carried out to determine how the attenuation of photons modifies the reconstructed counts obtained with this technique, and how this affects the accuracy of volume determination. Furthermore, we wanted to investigate how count-based determination of ventricle volumes is affected by the total SPET rotation angle and by different arm positions. We used micro -maps derived from computed tomography (CT) series of nine arbitrarily chosen patients to calculate a volume correction factor for each cardiac volume manually drawn on the CT images. An anthropomorphic chest phantom was used to confirm the calculation of correction factors. For the regions of the ventricles contained within a CT slice through the central part of the heart, the left to right volume ratio needed to be corrected by factors of 1.21 and 1.12 for 180 degrees and 360 degrees rotation, respectively. When all voxels within the left and right ventricles were included, the required volume ratio correction factor was close to 1. However, the variation among patients was larger for a 180 degrees (range 0.97-1.08) than for a 360 degrees rotation arc (range 1.0-1.03).