Multimodal target point assessment for stereotactic biopsy in children with diffuse bithalamic astrocytomas

INTRODUCTION

Diffuse glial tumors with bithalamic involvement are rare in children. Diagnostic assessment can be difficult as the radiological findings can be unspecific.

MATERIALS AND METHODS

In order to enhance the diagnostic yield metabolic imaging with MRS and PET using FET ( O-(2-[(18)F]fluoroethyl)- L-tyrosine) was performed in two children (2 and 10 years of age). Co-registered images were used for image-guided biopsy, which was planned with neuronavigation and stereotaxy simultaneously.

RESULTS

Biopsies from the right thalamus were planned, but locations were changed in both cases after metabolic imaging was available. MRS (thalamic voxel) was typical for a glial tumor in one child. In the older girl FET-PET revealed an unexpected lesion in the left cerebellar hemisphere, with a tumor-to-cortex ratio of 3.8, as against 1.7 in the thalamus. Accordingly, a stereotactic biopsy specimen was taken from the left cerebellar hemisphere, and a final diagnosis of anaplastic astrocytoma was made. The other patient showed a higher uptake (tumor-to-cortex ratio 1.6) in the left dorsal thalamus, compared with bilateral homogeneous hyperintensity of the thalamus structures on MRI. Stereotactic biopsy revealed a low-grade diffuse astrocytoma.

CONCLUSION

Stereotactic biopsy using metabolic imaging and image fusion can enhance the diagnostic yield in cases of diffuse pediatric gliomas disclosing unexpected 'hot spots'.

Uptake of cis-4-[18 F]fluoro-L-proline in scar formation: a marker of collagen synthesis?

Excessive scar formation is accompanied by abnormal collagen synthesis. The feasibility of monitoring collagen synthesis in vivo with no-carrier-added cis-4[18F]fluoro-L-proline (cis-FPro) was evaluated in an animal model with scar formation induced by implanted meshes. The abdominal wall of rats was replaced by alloplastic meshes. At days 3, 7, 14, 21 and 90 after implantation, the uptake of cis-FPro at 4 h post-injection was determined for resected samples of the mesh and normal tissues. The highest uptake was found in the kidneys (1.73+/-0.47%ID/g) followed by the liver (0.59+/-0.19%ID/g). The meshes showed the maximum uptake at day 3 (0.20+/-0.07%ID/g) with a decrease to 0.10+/-0.03%ID/g at day 90 (P<0.001). After 3 days no connective tissue was shown by histopathological morphometric analysis. The maximum partial volume (PV%) of connective tissue was 43+/-14 PV% 90 days after implantation. The maximum levels of granulocytes and inflammatory infiltrate were found at day 3 with minimal levels at day 90, paralleling the course of cis-FPro uptake. In conclusion, the uptake of cis-FPro at 4 h post-injection is not related to the content of connective tissue. Cis-FPro radiolabelled with 18F appears not to be a suitable radiopharmaceutical for in vivo monitoring of collagen synthesis in scar formation.

No-carrier-added (n.c.a.) synthesis of asymmetric [73,75Se]selenoethers with isonitriles

A new synthetic pathway for the preparation of no-carrier-added (n.c.a.) [73.75Se]selenoethers was investigated in order to enlarge the scope of available radioselenated compounds. Starting from n.c.a. 73,75Se(0), an isonitrile and an amine, the preparation of appropriate disubstituted radioselenoureas via homogenous and polymer-supported reactions was examined. Alkylation of these intermediates yielded the corresponding [73-75S]selenouronium salts. Hydrolysis under basic conditions provided the [73,75Se]alkylselenolates and a subsequent alkylation yielded various asymmetric [73-75Se]selenoethers with radiochemical yields of 13-56% within a reaction time of 130min in the homogenous phase and 35 min using the polymer-supported synthesis.

PET quantitation and imaging of the non-pure positron-emitting iodine isotope 124I

A series of PET studies using phantoms is presented to characterize the imaging and quantitative performance of the positron-emitting iodine isotope 124I. Measurements were performed on the 2D-PET scanner GE 4096+ as well as on the Siemens PET scanner HRR+ operated in both 2D and 3D modes. No specific correction was applied for the gamma-rays emitted together with the positrons. As compared to 18F, in studies with 124I there is a small loss of image resolution and contrast, and an increase in background. The quantitative results varied between different scanners and various acquisition as well as reconstruction modes, with an average relative difference of -6 +/- 13% (mean+/-SD) in respect of the phantom radioactivity as measured with gamma-ray spectroscopy. We conclude that quantitation of a radiopharmaceutical labelled with 124I is feasible and may be improved by the development of specific corrections.

Excitation functions of 85Rb(p,xn)(85m,g,83,82,81)Sr reactions up to 100 MeV: integral tests of cross section data, comparison of production routes of 83Sr and thick target yield of 82Sr

The beta+ emitter 83Sr (T(1/2) = 32.4 h, Ebeta+ = 1.23 MeV, Ibeta+ = 24%) is a potentially useful radionuclide for therapy planning prior to the use of the beta+ emitter 89Sr (T(1/2) = 50.5 d). In order to investigate its production possibility, cross section measurements on the 85Rb(p,xn)-reactions, leading to the formation of the isotopes (85m,g)Sr, 83Sr, 82Sr and 81Sr, were carried out using the stacked-foil technique. In a few cases, the products were separated via high-performance liquid chromatography. For 82Sr, both gamma-ray and X-ray spectrometry were applied; in other cases only gamma-ray spectrometry was used. From the measured excitation functions, the expected yields were calculated. For the energy range Ep = 37 --> 30 MeV the 83Sr yield amounts to 160 MBq/microA h and the level of the 85gSr (T(1,2) = 64.9 d) and 82Sr (T(1/2) = 25.5 d) impurities to <0.25%. In integral tests involving yield measurements radiostrontium was chemically separated and its radioactivity determined. The experimental production data agreed within 10% with those deduced from the excitation functions. The results of the 85Rb(p,3n)83Sr reaction were compared with the data on the production of 83Sr via the 82Kr(3He,2n)-process. In the energy range E3Hc = 18 --> 10 MeV the theoretical yield of 83Sr amounts to 5 MBq/microA h and the 82Sr impurity to about 0.2%. The method of choice for the production of 83Sr is thus the 85Rb(p,3n)-process, provided a 40 MeV cyclotron is available. During this study some supplementary information on the yield and purity of 82Sr was also obtained.

Electrochemical cell for separation of [18F]fluoride from irradiated 18O-water and subsequent no carrier added nucleophilic fluorination

An electrochemical cell was designed allowing the anodic deposition of n.c.a. [18F]fluoride solubilized in an 18O-water target and subsequent n.c.a. nucleophilic 18F-fluorination. The recovery of the deposited [18F]fluoride can be achieved in the presence of an aprotic solvent containing a phase-transfer catalyst (PTC). The radioisotope adsorbed electrochemically at the cylindrical surface of a glassy carbon electrode can be dried easily by washing the cell twice with dry aprotic solvents while maintaining a low electric field. This simple washing step makes an azeotropic drying process obsolete. Accordingly, less basic cryptates like [K within 2.2.2.]oxalate or triflate can be used for nucleophilic 18F-fluorination because loss of activity as a consequence of azeotropic drying under conditions of low basicity does not occur. The usefulness of this technique is exemplified for the n.c.a. synthesis of various 18F-labelled compounds. The radiotracers were synthesized with higher radiochemical yields and under much easier conditions than the conventional 18F-fluorination procedure which includes an additional drying step of the PTC.

Excitation functions of 124Te(d,xn)124,125I reactions from threshold up to 14 MeV: comparative evaluation of nuclear routes for the production of 124I

Excitation functions of the nuclear reactions 124Te(d,xn)124-125I were measured from their respective thresholds up to 14.0 MeV via the stacked-foil technique. Thin samples were prepared by electrolytic deposition of 99.8% enriched 124Te on Ti-backing. The excitation function of the 124Te(d,n)125I reaction was measured for the first time. The present data for the 124Te(d,2n)124I reaction are by an order of magnitude higher than the literature experimental data but are in good agreement with the results of a hybrid model calculation. From the measured cross sections, integral yields of 124,125I were calculated. The energy range Ed = 14 --> 10 MeV appears to be the best compromise between 124I-yield and 1251-impurity. The calculated 124I-yield amounts to 17.5 MBq/microA h and the 125I-impurity to 1.7%. A critical evaluation of the three nuclear routes for the production of 124I, viz. 124Te(d,2n)-, 124Te(p,n)- and 125Te(p,2n)-processes, is given. The reaction studied in this work proved to be least suitable. The 124Te(p,n)-reaction gives 124I of the highest radionuclidic purity, and a small-sized cyclotron is adequate for production purposes. The 125Te(p,2n)-reaction is more suitable at a medium-sized cyclotron: the yield of 124I is four times higher than in the other two reactions but the level of 0.9% 125I-impurity is relatively high.

Excitation functions of 125Te(p, xn)-reactions from their respective thresholds up to 100 MeV with special reference to the production of 124I

Excitation functions of the nuclear reactions 125Te(p, xn) (119,120m, 120g, 121,122,123,124,125)I were measured for the first time from their respective thresholds up to 100 MeV using the stacked-foil technique. Thin samples were prepared by electrolytic deposition of 98.3% enriched 125Te on Ti-backing. In addition to experimental studies, excitation functions were calculated by the modified hybrid model code ALICE-IPPE. The experimental and theoretical data generally showed good agreement. From the measured cross section data, integral yields of (123,124,125)I were calculated. The energy range Ep 21 --> 15 MeV appears to be very suitable for the production of the medically interesting radionuclide 124I (T(1/2) = 4.18 d; I(beta)+ = 25%). The thick target yield of 124I amounts to 81 MBq/microA h and the level of 125I-impurity to 0.9%. The 125Te(p,2n)124I reaction gives 124I yield about four times higher than the commonly used 124Te(p,n)124I and 124Te(d,2n)124I reactions. The proposed production energy range is too high for small cyclotrons but large quantities of 124I can be produced with medium-sized commercial machines.

Disturbance of serotonin 5HT2 receptors in remitted patients suffering from hereditary depressive disorder

AIM

The characteristics of 5HT2 receptor binding were investigated in major depression in vivo using positron emission tomography and the radioligand F-18-altanserin.

METHODS

Twelve patients from families with high loading of depression living in a geographically restricted region were examined and compared with normal control subjects. At the time of the PET measurement all patients were remitted; in some of them remission was sustained by antidepressive medication. Binding potential was assessed by Logan's graphical analysis method.

RESULTS

The binding of F-18-altanserin was about 38% lower in patients than in healthy controls (p < 0.001). A multiple regression analysis revealed that this difference was mainly induced by depression rather than by medication.

CONCLUSIONS

The data suggest that 5HT2 receptors are altered in depression. We present evidence for a reduction of the receptor density, which might be usable as trait marker of subjects susceptible for depressive illness.

3-[123I]Iodo-alpha-methyl-L-tyrosine uptake in cerebral gliomas: relationship to histological grading and prognosis

3-[123I]Iodo-alpha-methyl-L-tyrosine (IMT) is employed clinically as a tracer of amino acid transport in brain tumours using single-photon emission tomography (SPET). This study investigates the role of IMT SPET in the non-invasive histological grading and prognostic evaluation of cerebral gliomas. The files of patients investigated by IMT SPET in our clinic between 1988 and 1996 were evaluated retrospectively. Complete follow-up was available for 58 patients with cerebral gliomas investigated by IMT SPET shortly after tumour diagnosis. Seventeen patients had low-grade gliomas (WHO grade II), 14 had anaplastic gliomas (WHO grade III) and 27 had glioblastomas (WHO grade IV). Thirty-six cases were primary tumours and 22 cases, recurrences. Maximal and mean tumour-to-brain (T/B) ratios of IMT uptake at the first IMT SPET investigation were related to histological grading and survival time. Patients with low-grade gliomas showed significantly longer survival than patients with high-grade (grade III or IV) tumours. Gliomas without contrast enhancement on computed tomography or magnetic resonance imaging scans were associated with longer patient survival than tumours with contrast enhancement. The T/B ratios of IMT SPET showed no differences in relation to histological grading [WHO grade II: 1.73+/-0.59; WHO grade III: 1.74+/-0.38; WHO grade IV: 1.59+/-0.35, (mean+/-SD, T/B ratios of mean tumour uptake)]. The median survival time of patients with a high T/B ratio on IMT SPET was not significantly different from that of patients with a low T/B ratio (T/B ratio <1.6, 14.8 months; T/B ratio > or =1.6, 13.0 months). Thus, no evidence could be found for a relationship between IMT uptake in cerebral gliomas and either histological grading or survival time. Nevertheless, IMT SPET constitutes a useful method for the detection of primary and recurrent gliomas, determination of tumour extent and individual follow-up.

Uptake of cis-4-[18F]fluoro-L-proline in urologic tumors

Tumor uptake of the amino acid cis-4-[18F]fluoro-L-proline (cis-FPro) was studied with PET in eight patients with urologic tumors.

METHODS

Three patients had primary renal cell carcinomas (RCCs), one had a local recurrence of RCC, one had squamous RCC, one had an adrenal hemangioma, one had inguinal metastases of penile squamous carcinoma, and one had suspected metastatic disease from prostate cancer. PET scans of the trunk were acquired at 1 and 3-5 h after intravenous injection of 400 MBq cis-FPro and compared with 18F-FDG PET scans and CT.

RESULTS

None of the tumors or metastases showed significant uptake of cis-FPro. FDG uptake was seen in one of the three primary RCCs, in the local recurrence of RCC, in the squamous RCC, and in the metastases of penile cancer.

CONCLUSION

Cis-FPro appears not to be a promising PET tracer in oncology.

Whole-body kinetics and dosimetry of cis-4-[(18)F]fluoro-L-proline

The whole-body distribution of 4-cis[(18)F]fluoro-L-proline (cis-FPro) was studied in six patients with urological tumors by PET. Based on the IMEDOSE and MIRDOSE procedures radiation absorbed doses were estimated from whole-body PET scans acquired at 1 and 3-5 h after i.v. injection of 400 MBq cis-FPro. Cis-FPro showed high retention in the renal cortex and a slight uptake in liver and pancreas. Urinary excretion ranged from 12 to 19% at 5 h p.i. Highest absorbed doses were found for the urinary bladder wall and the kidneys (44.1/44.0 microGy/mbq). The effective dose according to ICRP 60 was 15.1 microSv/mbq for adults. This leads to an effective dose of 6.0 mSv in a PET study using 400 MBq cis-FPro.

3-[123I]iodo-alpha-methyl-L-tyrosine transport and 4F2 antigen expression in human glioma cells

3[(123)I]iodo-alpha-methyl-L-tyrosine is a tracer of amino acid transport in brain tumors using single-photon emission-computed tomography and predominantly transported by amino acid transport system L. The 4F2 antigen has been identified to be linked to system L-like transport and is assumed to be a part of the transporter protein. We demonstrated that system L-mediated transport of IMT and 4F2 antigen expression are dependent on proliferation rate of human glioma cells and significantly correlated with each other.

[The role of L-3-I-123-iodine-alpha-methyltyrosine SPECT in cerebral gliomas]

L-3-I-123-iodine-alpha-methyltyrosine (IMT) is a I-123-labelled amino acid which has been used for single photon emission computed tomography (SPECT) of cerebral gliomas for more than a decade. IMT-SPECT is able to detect tumor infiltration independent of disruptions of the blood-brain barrier which is often difficult with computed tomography or magnetic resonance tomography. The method is useful to detect tumor recurrences and helps to distinguish gliomas from non-neoplastic brain masses. IMT-SPECT is thus a valuable tool in the diagnostic evaluation and in therapy planning of patients with cerebral gliomas.

[123I]beta-CIT SPECT visualizes dopamine transporter loss in de novo parkinsonian patients

Parkinson's disease (PD) is characterized by degeneration of dopaminergic neurons in the basal ganglia, which may be visualized by single photon emission computed tomography (SPECT) in combination with the cocaine analog methyl-3-beta-(4-beta[123I]iodophenyl)tropane-2beta-carboxylate ([123I]beta-CIT). The aim of our study was to correlate findings of SPECT with clinical data of 34 previously untreated, idiopathic parkinsonian patients [age: 59.58+/-10.03 (mean+/-SD) years; Hoehn and Yahr Scale (HYS) mean range: 1.97+/-0.83, ranges I-III; Unified PD Rating Scale 3.0 (UPDRS, 30.64+/-18.68) and 15 healthy controls (age 47.93+/-10.47 years). SPECT scans were performed with a single-head gamma-camera 24 h after intravenous injection of [123I]beta-CIT. Comparison of the striatum/cerebellum (S/C) ratio of [123I]beta-CIT uptake of controls and parkinsonian subjects, subdivided according to their HYS range, was significant. No influence of age or sex was observed. Significant correlations were found between scores of the HYS, UPDRS parts I-III, part II, part III, and the S/C ratio of [123I]-CIT uptake. Moreover, SPECT with the radiotracer [123I]beta-CIT revealed side-to-side differences in parkinsonian patients and significant associations to contralateral clinical extrapyramidal symptomatology. Our data show that SPECT with [123I]beta-CIT is a valuable tool for estimating disease severity in PD.

Transport mechanisms of 3-[123I]iodo-alpha-methyl-L-tyrosine in a human glioma cell line: comparison with [3H]methyl]-L-methionine

The amino acid analog 3-[(123)I]iodo-alpha-methyl-L-tyrosine (IMT) is under clinical evaluation as a SPECT tracer of amino acid transport in brain tumors. This study investigated the carrier systems involved in IMT transport in human glioma cells in comparison with [3H-methyl]-L-methionine (3H-MET).

METHODS

Human glioma cells, type 86HG-39, were cultured and incubated for 1 min at 37 degrees C with IMT and 3H-MET in the lag phase (1.2 d after seeding), exponential growth phase (3 d after seeding), and plateau phase (8 d after seeding). Experiments were performed in the presence and absence of Na+, during inhibition of system L amino acid transport by 2-aminobicyclo[2.2.1 ]heptane-2-carboxylic acid (BCH), and during inhibition of system A amino acid transport by 2-(methylamino)-isobutyric acid (MeAIB).

RESULTS

IMT and 3H-MET uptake decreased by 55%-73% when the cells entered from the exponential growth phase into the plateau phase (P< 0.05; n = 3-11). Inhibition by BCH reduced uptake of IMT in the lag phase, exponential growth phase, and plateau phase by 90%-98% (P < 0.001; n = 3-6) and the uptake of 3H-MET by 73%-83% (P < 0.001; n = 3-11). In a Na+-free medium 3H-MET uptake was reduced by 23%-33% (P < 0.05; n = 3-11), whereas IMT uptake was not significantly different. MeAIB showed no significant effect on IMT or 3H-MET uptake in either phase.

CONCLUSION

Transport of both IMT and 3H-MET depends on the proliferation rate of human glioma cells in vitro and is dominated by BCH-sensitive transport. These data indicate that system L is induced in rapidly proliferating glioma cells and is the main contributor to the uptake of both tracers. 3H-MET transport showed a minor Na+ dependency that was not attributable to system A. The similarity of transport mechanisms of both tracers emphasizes the clinical equivalence of IMT SPECT and (11)C-MET PET for the diagnostic evaluation of gliomas.

Improved target system for production of high purity [18F]fluorine via the 18O(p,n)18F reaction

An improved aluminium target system for production of elemental fluorine via the 18O(p,n)18F reaction using a two-step irradiation protocol is described. In the first step highly enriched gaseous oxygen-18 is irradiated with protons to form fluorine-18 which gets deposited on the inner target surface. In the second step, after cryogenic recovery of oxygen-18 target gas, a mixture of elemental 'cold' fluorine and krypton is introduced and a short proton irradiation is done, whereby an isotopic exchange between the gaseous fluorine and the deposited radiofluorine occurs. The second step leads to the recovery of the radiofluorine as [18F]fluorine. Optimisation studies were performed regarding the yield and specific radioactivity of [18F]fluorine. Furthermore, some irradiation parameters relevant to the recovery step were investigated. It was found that a 15 to 20 min irradiation with a beam current of 20 microA is sufficient for the isotopic exchange between the fluorine-carrier and the 18F-radioactivity deposited on the inner wall of the target. The distribution of the 18F-radioactivity deposited on the inner target surface is inhomogeneous, probably due to convection effects. Extensive radioanalytical techniques were applied to characterise the reactivity of [18F]fluorine and to identify undesired nonreactive 18F-compounds, mainly [18F]tetrafluoromethane and [18F]nitrogentrifluoride. The [18F]fluorine produced in the system used has the distinction of having a negligible contamination from those inert 18F-compounds. This is a combined effect of the use of highest purity gases and a welded target construction, which avoids any contact of the gases with organic material during irradiations. The target has proved to be very reliable for production of [18F]fluorine in high yields of up to 34 GBq and specific activities of 350-600 GBq/mmol, both at 30 min after end of activation bombardment.

Excitation functions of 120Te(d,xn)121,120m,gI reactions from threshold up to 13.5 MeV: comparative studies on the production of 120gI

Excitation functions of the nuclear reactions 120Te(d,xn)121,120m,gI were measured for the first time from their respective thresholds up to 13.5 MeV. Thin samples prepared by electrolytic deposition of 99.0% enriched 120Te on Ti-backing were used. Integral yields of 121,120m,gI were calculated from the measured cross section data. A comparison of the 122Te(p,3n)-, 120Te(p,n)- and 120Te(d,2n)-processes for the production of 120gI is given. The 120Te(d,2n)-process is unsuitable for production purposes since the yield of 120gI is very low and the level of 121I impurity very high. The choice lies either on the 122Te(p,3n)- or the 120Te(p,n)-reaction and is governed by the available proton energy and the financial resources for procuring the enriched target material.