Geometric models in dosimetry of thyroid remnant mass

Aim: Absorbed dose to thyroid remnant tissue after 131I ablation becomes mass/size-dependent. This is a direct consequence of the small remnant size and radiation escape starts to be relevant. The self-absorbed fraction becomes mass/size-dependent. We have used Monte Carlo simulations to investigate the influence of the thyroid remnant shape upon the absorbed fraction calculation. Methods: Thyroid residue was modeled using spherical, cylindrical and elliptical shapes. Uniform beta activity distribution and unit density medium (water) within a remnant was assumed. For each of the geometrical models beta self-absorbed fraction (ϕγ) was calculated using Monte Carlo codes, while the mean absorbed dose per unit cumulated activity (Sγ) was calculated using MIRD formalism. Results: For spherical objects Ömono for mean beta energy (E = 0.182 MeV) of 131I is always greater than ϕγ calculated for the complete beta spectrum. For spheres having diameters 2–6 mm and assumption ϕγ=1, Sγ is overestimated by 11–37%. For cylinder and prolate spheroid of the same length and thickness, Sγ for cylinder is 30% smaller because of the greater mass. Similarly, elliptical cylinder and general ellipsoid of the same length and the same perpendicular dimensions (width and breadth), have similar ϕγ, while Sγ for elliptical cylinder is correspondingly smaller. Conclusion: For accurate dosimetry of thyroid remnants having masses <1 g and chordal lengths <1 cm it is necessary to calculate ϕγ for the full beta spectrum, or Sγ will be overestimated. The shape of the remnant may also be important since elongated non-spherical objects may also have ϕγ < 1.

Impact of DNA methylation on trophoblast function

The influence of epigenetics is evident in many fields of medicine today. This is also true in placentology, where versatile epigenetic mechanisms that regulate expression of genes have shown to have important influence on trophoblast implantation and placentation. Such gene regulation can be established in different ways and on different molecular levels, the most common being the DNA methylation. DNA methylation has been shown today as an important predictive component in assessing clinical prognosis of certain malignant tumors; in addition, it opens up new possibilities for non-invasive prenatal diagnosis utilizing cell-free fetal DNA methods. By using a well known demethylating agent 5-azacytidine in pregnant rat model, we have been able to change gene expression and, consequently, the processes of trophoblast differentiation and placental development. In this review, we describe how changes in gene methylation effect trophoblast development and placentation and offer our perspective on use of trophoblast epigenetic research for better understanding of not only placenta development but cancer cell growth and invasion as well.

7th International Congress of the Croatian Society of Nuclear Medicine

The Seventh International Congress of The Croatian Society of Nuclear Medicine gives an overview of present-day nuclear medicine. For the Congress 82 papers were selected: 50 for oral and 32 for poster presentation. Of 82 accepted papers 44 came from Croatia. Other papers came from Austria, Bosnia and Herzegovina, Germany, Greece, Hungary, Italy, Kosovo, Russia, Slovenia and Serbia. There were 16 lectures as part of CME programme. The congress shows that Croatian nuclear medicine follows general trends of the European nuclear medicine. This report includes a selection of abstracts that might interest the readers of Nuklearmedizin.

6th International Congress of the Croatian Society of Nuclear Medicine in Opatija 2008

The 6th International Congress of the Croatian Society of Nuclear Medicine gives an overview of present-day nuclear medicine. The congress shows that Croatian nuclear medicine follows the general trends of the European nuclear medicine.

Geometric models in dosimetry of thyroid remnant mass

AIM

Absorbed dose to thyroid remnant tissue after 131I ablation becomes mass/size-dependent. This is a direct consequence of the small remnant size and radiation escape starts to be relevant. The self-absorbed fraction becomes mass/size-dependent. We have used Monte Carlo simulations to investigate the influence of the thyroid remnant shape upon the absorbed fraction calculation.

METHODS

Thyroid residue was modeled using spherical, cylindrical and elliptical shapes. Uniform beta activity distribution and unit density medium (water) within a remnant was assumed. For each of the geometrical models beta self-absorbed fraction (varphi(beta)) was calculated using Monte Carlo codes, while the mean absorbed dose per unit cumulated activity (S(beta)) was calculated using MIRD formalism.

RESULTS

For spherical objects varphi(mono) for mean beta energy (E = 0.182 MeV) of 131I is always greater than varphi(beta) calculated for the complete beta spectrum. For spheres having diameters 2-6 mm and assumption varphi(beta) = 1, S(beta) is over-estimated by 11-37%. For cylinder and prolate spheroid of the same length and thickness, S(beta) for cylinder is 30% smaller because of the greater mass. Similarly, elliptical cylinder and general ellipsoid of the same length and the same perpendicular dimensions (width and breadth), have similar varphi(beta), while S(beta) for elliptical cylinder is correspondingly smaller.

CONCLUSION

For accurate dosimetry of thyroid remnants having masses <1 g and chordal lengths <1 cm it is necessary to calculate varphi(beta) for the full beta spectrum, or S(beta) will be overestimated. The shape of the remnant may also be important since elongated non-spherical objects may also have varphi(beta) < 1.

Osteogenic protein-1 (BMP-7) accelerates healing of scaphoid non-union with proximal pole sclerosis

We randomly assigned 17 patients with scaphoid non-union at the proximal pole to three treatment groups: (1) autologous iliac graft (n=6), (2) autologous iliac graft + osteogenic protein-1 (OP-1; n=6), and (3) allogenic iliac graft + OP-1 (n=5). Radiographic, scintigraphic, and clinical assessments were performed throughout the follow-up period of 24 months. OP-1 improved the performance of both autologous and allogenic bone implants and reduced radiographic healing time to 4 weeks compared with 9 weeks in group 1. Helical CT scans and scintigraphy showed that in OP-1-treated patients sclerotic bone was replaced by well-vascularised bone. The addition of OP-1 to allogenic bone implant equalised the clinical outcome with the autologous graft procedure. Consequently the harvesting of autologous graft can be avoided.

Dissecting a wheat QTL for yield present in a range of environments: from the QTL to candidate genes

Previous studies with 95 bread wheat doubled haploid lines (DHLs) from the cross Chinese Spring (CS)xSQ1 trialled over 24 yearxtreatmentxlocations identified major yield quantitative trait loci (QTLs) in homoeologous locations on 7AL and 7BL, expressed mainly under stressed and non-stressed conditions, respectively. SQ1 and CS contributed alleles increasing yield on 7AL and 7BL, respectively. The yield component most strongly associated with these QTLs was grains per ear. Additional results which focus on the 7AL yield QTL are presented here. Trials monitoring agronomic, morphological, physiological, and anatomical traits revealed that the 7AL yield QTL was not associated with differences in flowering time or plant height, but with significant differences in biomass at maturity and anthesis, biomass per tiller, and biomass during tillering. In some trials, flag leaf chlorophyll content and leaf width at tillering were also associated with the QTL. Thus, it is likely that the yield gene(s) on 7AL affects plant productivity. Near-isogenic lines (NILs) for the 7AL yield QTL with CS or SQ1 alleles in an SQ1 background showed the SQ1 allele to be associated with >20% higher yield per ear, significantly higher flag leaf chlorophyll content, and wider flag leaves. Epidermal cell width and distance between leaf vascular bundles did not differ significantly between NILs, so the yield-associated gene may influence the number of cell files across the leaf through effects on cell division. Interestingly, comparative mapping with rice identified AINTEGUMENTA and G-protein subunit genes affecting lateral cell division at locations homologous to the wheat 7AL yield QTL.

A high-density genetic map of hexaploid wheat (Triticum aestivum L.) from the cross Chinese Spring x SQ1 and its use to compare QTLs for grain yield across a range of environments

A population of 96 doubled haploid lines (DHLs) was prepared from F1 plants of the hexaploid wheat cross Chinese Spring x SQ1 (a high abscisic acid-expressing breeding line) and was mapped with 567 RFLP, AFLP, SSR, morphological and biochemical markers covering all 21 chromosomes, with a total map length of 3,522 cM. Although the map lengths for each genome were very similar, the D genome had only half the markers of the other two genomes. The map was used to identify quantitative trait loci (QTLs) for yield and yield components from a combination of 24 site x treatment x year combinations, including nutrient stress, drought stress and salt stress treatments. Although yield QTLs were widely distributed around the genome, 17 clusters of yield QTLs from five or more trials were identified: two on group 1 chromosomes, one each on group 2 and group 3, five on group 4, four on group 5, one on group 6 and three on group 7. The strongest yield QTL effects were on chromosomes 7AL and 7BL, due mainly to variation in grain numbers per ear. Three of the yield QTL clusters were largely site-specific, while four clusters were largely associated with one or other of the stress treatments. Three of the yield QTL clusters were coincident with the dwarfing gene Rht-B1 on 4BS and with the vernalisation genes Vrn-A1 on 5AL and Vrn-D1 on 5DL. Yields of each DHL were calculated for trial mean yields of 6 g plant(-1) and 2 g plant(-1) (equivalent to about 8 t ha(-1) and 2.5 t ha(-1), respectively), representing optimum and moderately stressed conditions. Analyses of these yield estimates using interval mapping confirmed the group-7 effects on yield and, at 2 g plant(-1), identified two additional major yield QTLs on chromosomes 1D and 5A. Many of the yield QTL clusters corresponded with QTLs already reported in wheat and, on the basis of comparative genetics, also in rice. The implications of these results for improving wheat yield stability are discussed.

Bone marrow immunoscintigraphy in haematological patients with pancytopenia: preliminary results

The aim of this study was to assess the clinical value of bone marrow immunoscintigraphy using the (99m)Tc labelled anti-NCA-95 antigranulocyte antibodies (AGAb) and of AGAb bone marrow uptake ratio (UR) in the initial diagnostic work-up of diseases with depression of the bone marrow. Twenty-four whole-body bone marrow scans were performed in 23 patients (11 women, 12 men; median age 46 years, range 17-74 years) 5 h after i.v. injection of 370 MBq of AGAb. The UR was calculated from the posterior view drawing an irregular region of interest around the sacroiliac and a background areas. The mean UR in pancytopenic patients was 2.3+/-1.5 (range 0.3-5.8), thus being significantly lower (P=0.45 x 10(-6)) than the mean UR in a control group of 50 patients (mean UR 7.3+/-2.3; range 4.4-12.6) obtained previously. Considering patient age, there was no overlap between UR of pancytopenic patients and the respective normal ranges. The bone marrow appearance on scans seemed to be characteristic for the different haematological diseases investigated. In six patients with myelofibrosis, bone marrow scans demonstrated diffusely decreased bone marrow activity and prominent splenic uptake, possibly related to extramedullary haematopoiesis. In aplastic anaemia, highly reduced and patchy marrow uptake was observed in four patients (five scans), in one of them persisting even after blood cell counts had recovered to the near-normal range. In another two patients with aplastic anaemia, diffusely decreased bone marrow uptake was obtained. In patients with myeloid leukaemia, bone marrow patterns were almost normal probably because the target antigen is often expressed on neoplastic myeloid cells, too. Bone marrow extension was a common finding in these patients. There is an obvious differentiation between haematological patients with pancytopenia and normal subjects by means of AGAb bone marrow uptake ratio. The distinct patterns of AGAb distribution may be indicative for particular haematological diseases.

Triple-head gamma camera PET: system overview and performance characteristics

Positron emission tomography (PET) is currently performed using either a dedicated PET scanner or scintillation gamma camera equipped with electronic circuitry for coincidence detection of 511 keV annihilation quanta (gamma camera PET system). Although the resolution limits of these two instruments are comparable, the sensitivity and count rate performance of the gamma camera PET system are several times lower than that of the PET scanner. Most gamma camera PET systems are manufactured as dual-detector systems capable of performing dual-head coincidence imaging. One possible step towards the improvement of the sensitivity of the gamma camera PET system is to add another detector head. This work investigates the characteristics of one such triple-head gamma camera PET system capable of performing triple-head coincidence imaging. The following performance characteristics of the system were assessed: spatial resolution, sensitivity, count rate performance. The spatial resolution, expressed as the full width at half-maximum (FWHM), at 1 cm radius is 5.9 mm; at 10 cm radius, the transverse radial resolution is 5.3 mm, whilst the transverse tangential and axial resolutions are 8.9 mm and 13.3 mm, respectively. The sensitivity for a standard cylindrical phantom is 255 counts.s(-1).MBq*(-1)), using a 30% width photopeak energy window. An increase of 35% in the PET sensitivity is achievable by opening an additional 30% width energy window in the Compton region. The count rate in coincidence mode, at the upper limit of the systems optimal performance, is 45 kc.s(-1) (kc=kilocounts) using the photopeak energy window only, and increases to 60 kc.s(-1) using the photopeak + Compton windows. Sensitivity results are compared with published data for a similar dual-head detector system.

Tc-99m DTPA renal scintigraphy using deconvolution analysis with six functional images of the mean time to evaluate acute pyelonephritis

In 38 children with proved P-fimbriated Escherichia coli acute pyelonephritis, Tc-99m DTPA dynamic renal scintigraphy in the zoom mode using deconvolution analysis was performed, and the results were compared with those of Tc-99m DMSA scans. From the dynamic study, six functional images of the mean time were generated. Each functional image was analyzed separately to search for focal areas of increased mean time within the kidney contour, especially over the kidney parenchyma. Time-activity curves from these areas were generated and analyzed. Tc-99m DMSA scintigraphy showed generalized or focal decreased uptake in 32 (41.8%) kidneys, and deconvolution analysis of Tc-99m DTPA scintigraphy revealed pathologic renographic curves in 58 (77.6%) kidneys. Prolonged whole-kidney and normal renal parenchymal transit times (dilatation without obstruction) were found in 38 (50%) kidneys, whereas prolonged whole-kidney and renal parenchymal transit times (dilatation with obstruction) were observed in 20 (27.6%) kidneys. Separate analysis of each of the six functional images of the mean time showed focal areas of increased mean time in the kidney parenchyma of 11 kidneys. In five cases, time-activity curves from these areas showed a sharp increase of activity on the descending part of the curve, which might reflect the return of urine from the collecting system into kidney cortex (i.e., intrarenal reflux). These results showed that in a urinary tract with acute pyelonephritis, urodynamic changes may lead to obstructive nephropathy and intrarenal reflux. Tc-99m DTPA renal scintigraphy in the zoom mode using deconvolution analysis with six functional images of the mean time has proved to be a valuable method to evaluate acute pyelonephritis, thus allowing dynamic and morphologic analysis of the urinary tract at the same time.

Determination of small objects from pinhole scintigrams

This study assessed the possibility of measuring the linear dimensions of small structures using pinhole scintigraphy. A number of glass objects were made with a spherical, cylindrical or conical shape. Their maximum dimensions (diameters and heights) were 3.5-22.5 mm. These glass objects were filled with 131I, placed inside a plastic neck phantom and imaged using a gamma camera equipped with a pinhole collimator. The source-to-collimator distance was varied from 2 to 12 cm. An algorithm for image segmentation (threshold selection) was used to divide the image into object and background. On the segmented image, the number of non-zero pixels in the direction of the principal axes was multiplied by the appropriate calibration factor to obtain the linear dimensions of the object. Spatial resolution of the pinhole collimator, expressed as the full-width at half-maximum (FWHM), varied from 8 to 10 mm for the range of source-to-collimator distances examined. We found that, for dimensions up to 1.5 x FWHM, finite spatial resolution affects the accuracy of measurement. Non-linear correlation between true and calculated dimensions was used to take the latter into account. Our results are now being used to improve quantitation of remnant thyroid tissue masses for the calculation of radioiodine ablation doses.

Radioiodine uptake in thyroid cancer patients after diagnostic application of low-dose 131I

The aim of this study was to investigate the influence of the diagnostic administration of 74 MBq 131I on subsequent uptake of therapeutic radioiodine in thyroid cancer patients. Retention measurements were performed using a whole-body counter in 24 patients 6 weeks after total thyroidectomy. Profile scans were performed 2, 24, 48 and 72 h after the administration of the diagnostic dose and 72 h after the administration of the ablation-therapeutic dose (4.4 GBq). The mean ( +/- S.D.) effective half-life of the diagnostic dose in thyroid remnants was 40.3 +/- 23.0 h. The uptake in the thyroid remnants of the subsequent ablation dose 72 h after administration was 30.4 +/- 19.8% of that predicted from the diagnostic study. The greater reduction in uptake was associated with the longer half-life of iodine and higher uptake in the thyroid remnants at 24 h, with a longer interval between surgery and administration of the diagnostic dose and a shorter period between administration of the diagnostic and ablation doses. Our results show that a diagnostic dose of 74 MBq 131I markedly reduces thyroid uptake of an ablation dose of 131I. This should be taken into account during radiation dose planning whenever a quantitative dosimetric study is to be performed.

Detection of diffuse skeletal lesions by monitoring the kinetics of labeled phosphonate

A method of detecting of diffuse skeletal involvement in patients with metastatic tumors or with metabolic diseases is presented. The study consisted of 31 patients without bone disease and of 26 selected patients with diffuse skeletal involvement. The kinetics of 99mTc-dicarboxypropane diphosphonate (DPD) were calculated by monitoring the plasma and urine concentrations up to 5 hours after administration. Using these data, the renal clearance as well as the increase in urinary excretion of 99mTc-DPD were determined. The results indicate that measurement of the quantity of 99mTc-DPD excreted in the urine after 3 hours allows a reliable separation of the patients with diffuse skeletal lesions from normals. Other calculations such as renal clearance as well as the drop in plasma concentration were less sensitive. The test may be performed simultaneously with bone scintigraphy without additional radiation burden to the patient.

Detection of Diffuse Skeletal Lesions by Monitoring the Kinetics of Labeled Phosphonate

A method of detecting of diffuse skeletal involvement in patients with metastatic tumors or with metabolic diseases is presented. The study consisted of 31 patients without bone disease and of 26 selected patients with diffuse skeletal involvement. The kinetics of 99mTc-dicarboxypropane diphos-phonate (DPD) were calculated by monitoring the plasma and urine concentrations up to 5 hours after administration. Using these data, the renal clearance as well as the increase in urinary excretion of 99mTc-DPD were determined. The results indicate that measurement of the quantity of 99mTc-DPD excreted in the urine after 3 hours allows a reliable separation of the patients with diffuse skeletal lesions from normals. Other calculations such as renal clearance as well as the drop in plasma concentration were less sensitive. The test may be performed simultaneously with bone scintigraphy without additional radiation burden to the patient.

Effect of imaging time on the values of the sacroiliac index

Quantitative scintigraphy of the sacroiliac joints was performed in a group of normal subjects and a group of subjects with unilateral and bilateral sacroiliitis. The aim of the study was to determine whether the time intervals of imaging had any effect on the values of the sacroiliac index. Imaging was performed every 30 min up to 300 min and the indices were calculated at the time intervals mentioned. We found that the values of the sacroiliac index increased in the group of normal subjects until 150 min after the application of the radiopharmaceutical, and that in the group of subjects who had sacroiliitis they increased until 210 min. The results show that the time interval optimal to quantitative sacroiliac joint imaging is at least 3 1/2 h after administration of the radiopharmaceutical.

The value of early and late 99mTc-methylene diphosphonate scintigrams of hands in patients with rheumatoid arthritis and other inflammatory rheumatic diseases

Scintigrams of hands performed immediately after injection of 555 MBq 99mTc-methylene disphosphonate (99mTc-MDP) have been found to be the same and to have the same diagnostic value as those performed with 99mTcO4 both in persons without arthritic changes and in patients with inflammatory rheumatic diseases. Increased accumulation at this point is caused by hypervascularity due to inflammation, bone accretion being still negligible. Additional exposure to radiation from 99mTcO4 scintigraphy can therefore be avoided. The late scintigrams performed 3 h after 99mTc-MDP injection in the same patient can give us additional information on the amount of bone remodeling caused by chronic inflammation. Comparison of early and late scintigrams and the radiographs of hands in the same patient can provide us with better understanding of intensity, duration, and nature of joint changes under observation.

Influence of age on quantitative sacro-iliac joint imaging

Computer processing of sacro-iliac (S-I) joint scintigrams represents a significant contribution to the diagnostic workup of this area. The S-I index is calculated as the ratio between the total number of counts in the region of interest placed on the S-I joint and an identical region placed on the sacrum. S-I indexes were determined in a group of 70 patients aged 13-77 years to establish the influence of age on normal index values. Our results indicate that S-I index values are age dependent. The study was performed 2 h post-injection but the possibility exists that this is not the optimal time interval.

Bone scintigraphy in idiopathic aseptic femoral head necrosis (IAFHN)

Idiopathic aseptic femoral head necrosis (IAFHN) is a disease of unknown aetiology most commonly affecting adults, producing functional impairment of the hip joint and immobility. Characteristic macroscopic, microscopic and radiologic features include: (1) changes in joint cartilage, (2) subchondral necrotic area, (3) changes in fibrous tissue, and (4) osteosclerosis and vascular proliferation. The diagnosis is based on clinical and X-ray examinations. More recently scintigraphy has been used in diagnosing IAFHN. It is a very sensitive, but non-specific method. Nineteen patients aged 25-57 years were included in our study. Scintigrams were divided in four groups: (1) normal, (2) uniformly increased activity in the femoral head, (3) non-uniformly increased activity in the femoral head, and (4) a photon deficient area in the femoral head. A comparison of scintigraphy and radiological examination suggests that a photon deficient area corresponds with stage III of radiological classification, non-uniformly increased activity with stage II, and uniformly increased activity with stage I. These results indicate that scintigraphy can be used for staging of disease.