[Results of fine needle aspiration biopsy, frozen section diagnosis and definite histological results in thyroid pathology. Report of 163 cases]. / Analyse des résultats de la cytoponction, de l'examen histologique extemporané et définitif dans le traitement chirurgical de la pathologie thyroïdienne: à propos de 163 cas.

INTRODUCTION: In thyroid diseases, the place of fine needle aspiration biopsy still continues to be discussed: the sensibility and specificity vary greatly in the literature. Frozen section diagnosis is necessary to form a diagnostic strategy. The objective of this study was compare the results of fine needle aspiration biopsy, frozen section diagnosis, and definitive histologic results in a population of 163 patients and to draw conclusions about treatment. MATERIAL AND METHOD: From 1994 to 1999, 163 patients (132 females and, 31 males) undergoing thyroid surgery were included in this retrospective study, after a standard preoperative work-up. Those with a single palpable nodule and hypofixation on scintigraphy underwent fine needle aspiration before surgery. These results were compared with the definitive histologic results. RESULTS: A loboisthmectomy was performed in 88 cases (54%), a subtotal thyroidectomy in 34 cases (21%), and a total thyrodectomy in 41 cases (25%). In the latter group, an associated neck dissection was performed in 18 cases (11%); a frozen section diagnosis was obtained in all cases of thyroid nodules. This study demonstrated a single nodule in 97 cases (60%), multiple nodules in 27 cases (17%), multinodular goitre in 34 cases (21%), and 5 Basedow diseases (3%). Sixty-two cases (38%) of thyroid nodules underwent fine needle aspiration before surgery. In 25 cases (15%), definitive pathology showed a malignant lesion. The frozen section diagnosis had a sensitivity of 73% and a specificity of 99%, and the fine needle aspiration biopsy had a sensitivity of 40% and a specificity of 100%. CONCLUSION: The authors propose fine needle aspiration biopsy in the following cases: a single palpable nodule and hypofixation on scintigraphy or a surgical contra indication; and direct surgery in symptomatic thyroid disease or if there are one or several full nodules > 2 cm. In near future, these indications will be modified with the increasing reliability of fine needle aspiration biopsy.

Non-medical exposure to radioiodines and thyroid cancer.

The Chernobyl accident, which occurred 32 years after the accidental exposure of Marshall islanders, resulted in the exposure of neighbouring populations to a mixture of iodine isotopes and in an increased incidence of thyroid cancer. The highest thyroid doses were received by the youngest age groups. This review describes the existing evidence, and examines factors that may have increased the risk. It also stresses problems with contemporary thyroid measurements, and the lack of information on the sensitivity of the thyroid to short-lived iodine isotopes and iodine-131. Practical considerations for nuclear physicians, epidemiologists and thyroidologists are discussed in the light of this major accident.

Tissular distributions and kinetics of two renal 99mTc-radiopharmaceuticals in rat.

A digital radioimager (RI), conventional radioautography (RA), and tracks microradioautography (MRA) were used to assess the biodistributions and kinetics of 99mTc-dimercaptosuccinic (99mTc-DMSA) and 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) in rat at both macroscopic and microscopic levels. Three groups of male Wistar rats were studied. Using gamma-counting, kidney, liver, spleen and blood kinetics of both tracers were assessed in the three groups. Using RA and RI, renal slices were analyzed in group 1 the animals being sacrified from 2 to 60 min after injection of 99mTc-MAG3, and in group 2 the animals being sacrificed from 0.5 to 24 hr after injection of 99mTc-DMSA. Using MRA, renal slices were analyzed for 99mTc-DMSA (group 3). RA films and RI images displayed the variation with time of the cortical and medullary uptakes of the tracers. No regional heterogeneity within the different structures could be seen neither with RA films nor with MRA. The remaining activity in the blood 24 hr after injection of 99mTc-DMSA was evaluated. The tissular distributions of both tracer being homogenous, mean values of cortical uptake seems to be acceptable for dosimetric studies. Our results incite to use of 99mTc-MAG3 instead of 99mTc-DMSA when both tracers may be indicated.

Total body 4.5 Gy gamma irradiation-induced early delayed learning and memory dysfunction in the rat.

In an attempt to determine the consequences of total body radiation damage on learning and memory in the rat, twenty-eight male Wistar rats aged 4 months received 4.5 Gy total body gamma-irradiation (TBI) while 28 rats received sham irradiation. Sequential behavioral studies of negative reinforcement including a/ one- and b/ two-way avoidance tasks were undertaken. a/ One-way avoidance test: this test was performed before and after TBI. Prior to irradiation both groups were similar. At 20 days (D) and at 3 months post-TBI, irradiated rats had a significantly lower percentage of avoidance than controls but no statistical difference was found at 5 months post-TBI. b/ Two-way avoidance test: this test was performed only after TBI. At days 21, 22, 23, 24, (leaming) and at 4 or 6 months (recalls) post-TBI the mean percentage of avoidance was significantly lower in irradiated than in control rats. This study demonstrates that total-body exposure to 4.5 Gy gamma-irradiation induces behavioral dysfunction affecting learning and transitorily memory. These results suggest that a relatively low dose of total body irradiation can induce neurological complications, which persist 4-6 months later.

Highlights of the European Association of Nuclear Medicine Congress, Paris 2000.

The recent European Association of Nuclear Medicine Congress, "Paris 2000", was an exceptional success, as illustrated by the record attendance. This review discusses some of the key new findings presented at the Congress in the fields of neurology, cancer therapy, cancer diagnosis, cardiology and miscellaneous other areas. The progress being made indicates that nuclear medicine has a bright future in the new millennium.

Scintigraphic screening for renal damage in siblings of children with symptomatic primary vesico-ureteric reflux.

OBJECTIVE: To define prospectively the incidence of renal parenchymal lesions in the siblings of patients treated at one institution for primary vesico-ureteric reflux (VUR). PATIENTS AND METHODS: From January 1997 to October 1998, a prospective study including renal scintigraphy (using dimercaptosuccinic acid, DMSA) and a radionuclide cystogram was proposed systematically to the asymptomatic siblings of children treated for primary VUR. The radionuclide cystograms were interpreted as showing the presence or absence of VUR and the DMSA scan as symmetrical or asymmetrical differential function, with or with no renal defect. RESULTS: Fifty-five families gave informed consent, of whom 46 completed the study (eight refused secondarily and one was omitted by exclusion criteria), representing 46 symptomatic patients and 65 siblings. There were 17 siblings with VUR (26%) including two of 13 infants and 15 of 52 children aged > 18 months. One radionuclide cystogram failed. Of the 17 refluxing siblings, four had a history of symptomatic urinary tract infection; 62 of the 65 siblings had a DMSA scan, of which 56 were normal and six (10%) showed abnormalities (five asymmetrical differential function and one parenchymal defect). Only one of these six patients had VUR at the time of the evaluation and only one had a small kidney detected by ultrasonography on one side (and no VUR). There were no adverse effects associated with screening. CONCLUSION: This study confirms a significant overall incidence of VUR (26%) in the asymptomatic siblings of patients treated for primary VUR. From the results of the DMSA scan (only one sibling had a parenchymal defect), the systematic screening of asymptomatic siblings does not appear to be beneficial.

[Effect of Ginkgo biloba extract (EGb 761) on rats in an experimental model of acute encephalopathy after total body irradiation]. / Effet de l'extrait de Ginkgo biloba (EGb 761) chez le rat sur un modèle expérimental d'encéphalopathie aiguë après irradiation corporelle totale.

PURPOSE: To define the therapeutic effect of Ginkgo biloba extract (EGb 761) in an experimental model of acute encephalopathy following total body irradiation in rats. MATERIAL AND METHODS: Ninety four-month-old rats received 4.5 Gy total body irradiation (TBI) at day 1 while 15 rats received sham irradiation. A behavioural study based on a conditioning test of negative reinforcement, the one-way avoidance test, was performed test, was performed after irradiation. Orally treatment was started one day (study A) or twenty two days (study B) after irradiation and repeated daily for twelve days. In the irradiated group, three subgroups were defined according to the treatment received: EGb 761 (50 mg/kg), EGb 761 (100 mg/kg), water. RESULTS: This work comprised two consecutive studies. In study A (45 rats) the one-way avoidance test was administered daily from day 7 to day 14. In study B (45 rats) the behavioural test was performed from day 28 to day 35. Study A (three groups of 15 rats): following TBI, irradiated rats treated with water demonstrated a significant delay in a learning the one-way avoidance test in comparison with sham-irradiated rats (P < 0.0002) or irradiated rats treated with EGb 761 (50 mg/kg; P < 0.0017) or EGb 761 (100 mg/kg; P < 0.0002). The irradiated rats, treated with EGb 761 (50 or 100 mg/kg) did not differ from the sham-irradiated controls. Study B (three groups of 15 rats): the irradiated rats, treated with water or EGb 761 (50 or 100 mg/kg) did not differ from the sham-irradiated controls. CONCLUSION: This study indicates that a relatively low dose of total body irradiation induces a substantial acute learning dysfunction in the rat, which persists fourteen days after TBI. This effect is prevented by the administration of EGb 761 (50 or 100 mg/kg) started twenty-four hours after irradiation.

Contribution of single-photon emission computed tomography in the diagnosis and follow-up of CNS toxicity of a cytarabine-containing regimen in pediatric leukemia.

PURPOSE: Cytarabine (ara-C) is one of the most effective chemotherapeutic agents in patients with acute leukemia (AL), with a clear dose effect. Use of high-dose ara-C is hampered, however, by a noticeable toxicity, particularly to the CNS. We investigated the usefulness of CNS perfusion imaging with technetium-99m ((99m)Tc)-hexamethyl-propylene-amine oxime (HMPAO) single-photon emission computed tomography (SPECT) concurrent to magnetic resonance imaging (MRI) to specifically assess the effects of standard- and high-dose ara-C in children with AL. PATIENTS AND METHODS: Twenty-six perfusion studies using (99m)Tc-HMPAO SPECT were performed in 12 children (age range, 4 to 15 years) with AL after induction therapy, which consisted of a standard-dose ara-C, immediately after consolidation with high-dose ara-C, and later during follow-up (range, 6 to 44 months). The chemotherapy-related adverse events were monitored and correlated to SPECT and MRI. RESULTS: After the induction phase, all children were neurologically normal on MRI. On SPECT imaging, four children displayed a slightly heterogeneous perfusion. After high-dose ara-C (4 to 36 g/m(2)), five children had regressive neurologic signs of potential toxic origin. Of these five children, only one had an abnormal MRI scan, whereas all patients showed evidence of diffuse cerebral and/or cerebellar heterogeneous perfusion on SPECT. The seven other patients without any neurologic symptoms had normal MRI scans; SPECT was normal for three patients and abnormal for four patients. On follow-up, for four children who had presented with clinical neurologic toxicity, SPECT improved in three patients and remained unchanged in one patients. In two of these four children, delayed abnormalities (T2 white matter hypersignal and cerebellar atrophy) appeared on MRI scans. CONCLUSION: In our series, diffuse heterogeneous brain hypoperfusion is often the sole early objective imaging feature identified by SPECT of high-dose ara-C neurotoxicity, where MRI still demonstrates normal pictures.

Cell irradiation caused by diagnostic nuclear medicine procedures: dose heterogeneity and biological consequences.

Most radionuclides used for diagnostic imaging emit Auger electrons (technetium-99m, iodine-123, indium-111, gallium-67 and thallium-201). Their very short range in biological tissues may lead to dose heterogeneity at the cellular level with radiobiological consequences. This report describes the dosimetric models used to calculate the mean dose absorbed by the cell nucleus from Auger radionuclides. The techniques used to determine the biodistribution of radiopharmaceuticals at the subcellular level are also described and compared. Published examples of cellular dosimetry computations performed with radiotracers are reviewed in various clinical settings. Finally, the biological implications of the subcellular localization of Auger emitters are examined. While a number of efforts have been made to obtain dosimetric models and to estimate subcellular distribution of radioactivity, little is known of the cellular dosimetry of most radiopharmaceuticals used in diagnostic imaging. However, biological examples of selective radiotracer uptake have been shown, leading to extremely strong cell-cell dose heterogeneity. Furthermore, radiobiological experiments show that the biological effects of Auger emitters incorporated into DNA can be severe, with relative biological effectiveness greater than 1 compared with external X-rays. These findings clearly show that the assessment of biological risks associated with internal administration of diagnostic radiopharmaceuticals must focus not only on target organs as a whole, but also on the cellular level. This review proposes the most appropriate model for dosimetric computations (cellular or conventional) according to the subcellular distribution of radiotracers. The radionuclide of choice and the general strategy used to design new diagnostic radiopharmaceuticals are also discussed.

Biological consequences of the heterogeneous irradiation of lymphocytes during technetium-99m hexamethylpropylene amine oxime white blood cell labelling.

Technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO) labelling of white blood cells, routinely used for the detection of infection, results in the incorporation of radioactivity by polymorphonuclear leucocytes and also lymphocytes and can induce cell lesions in the latter case. The aim of this study was therefore to acquire data on the morphological and functional status of labelled lymphocytes present in the 99mTc-HMPAO leucocyte mixture and to determine the cellular consequences of labelling. The mean radioactivity associated with lymphocytes was 325 +/- 10.8 kBq/10(6) lymphocytes under standard labelling conditions. Microautoradiographic studies showed that labelling was heterogeneous (4% intensely labelled cells), which prevented calculation of the mean absorbed dose. The frequency of chromosomal aberrations (dicentrics and rings) in the labelled lymphocytes for 380 kBq/10(6) cells was 1.08 +/- 0.09 but no abnormality was observed in the unlabelled control lymphocytes. The plating efficiency of labelled lymphocytes was reduced, as compared with that for control cells, but some lymphocytes were still able to form clones and were still "alive" by radiobiological definition. It is therefore suggested that lymphocytes should be removed from 99mTc-HMPAO cell preparations before administration to patients.

[Urology and nuclear medicine in children. Experience from a series of 1200 renal scintigraphies]. / Médecine nucléaire en urologie pédiatrique. A propos d'une série de 1,200 scintigraphies rénales.

During the last 4 years, we have performed 1200 renal scintigraphies in children under the age of 6 years: 57% of dynamic renal scintigraphies using MAG3 for antenatally diagnosed uropathies (mainly pelvic dilatations and megaureters), 36% of static renal scintigraphies using DMSA for renal sequelae of pyelonephritis with or without vesicoureteric reflux, and 6% of direct isotope cystography for follow-up of vesicoureteric reflux. Renal scintigraphy, which provides low radiation hazards (1 mSv), is now a major imaging modality for paediatric urinary tract disease.

Comparison of cellular and conventional dosimetry in assessing self-dose and cross-dose delivered to the cell nucleus by electron emissions of 99mTC, 123I, 111In, 67Ga and 201T1.

The radionuclides used in nuclear medicine imaging emit numerous mono-energetic electrons responsible for dose heterogeneity at the cellular level. S(self) the self-dose per unit cumulated activity (which results from the radionuclide located in the target cell), and S(cross) the cross-dose per unit cumulated activity (which comes from the surrounding cells) delivered to a target cell nucleus by electron emissions of technetium-99m, iodine-123, indium-111, gallium-67 and thallium-201 were computed at the cellular level. An unbounded close-packed hexagonal cell arrangement was assumed, with the same amount of radioactivity per cell. Various cell sizes and subcellular distributions of radioactivity (nucleus, cytoplasm and cell membrane) were simulated. The results were compared with those obtained using conventional dosimetry. S(self) and S(cross) values depended closely on cell dimensions. While the self-dose depended on the tracer distribution, the latter affected the cross dose by less than 5%. When the tracer was on the cell membrane, the self-dose was particularly low compared to the cross-dose, as the self-dose to cross-dose ratio was always less than 11%. In the case of cytoplasmic or cell membrane distribution of radioactivity, conventional electron dosimetry slightly overestimated the dose absorbed by the target cell nucleus (by 1.08-to 1.7-fold). In contrast, conventional dosimetry strongly underestimated the absorbed dose (1.1- to 75-fold) when the radioactivity was located in the nucleus. The discrepancies between conventional and cellular dosimetry call for calculations at the cellular level for a better understanding of the biological effects of radionuclides used in diagnostic imaging.

Heterogeneous distribution of technetium-99m-labeled microspheres in rat lungs: microautoradiographic evidence and dosimetric consequences.

UNLABELLED: The heterogeneity of 99mTc-labeled microspheres distribution within rat lung was visualized and quantified using a microautoradiographic "track" method (MAR). METHODS: MAR was used to study the uptake of radioactivity by individual microspheres, thereby enabling calculation of the range of particle activity. MAR was also used to visualize in rat lung sections the intrapulmonary distribution of the microspheres within the lungs after intravenous administration. The mean doses delivered to the cells in close contact with the labeled microspheres were calculated taking only the 99mTc electron emissions into account. RESULTS: All the microspheres were labeled. Nevertheless, the spectrum of visible tracks varied by a factor of 10, inducing a variable activity per microsphere from < 36 Bq to 325 Bq (mean activity-94 Bq/microsphere). No correlation existed between the radioactivity uptake and the size of microspheres. A very heterogeneous tridimensional distribution of the microspheres within the lungs were demonstrated with interparticle distances ranging from 57-4400 microns. On the other hand, only 1 of 2000 rat lung capillaries was obstructed. Using the mean activity, calculated delivered doses were found to reach approximately 6 Gy for the closest endothelial cells and 2 Gy for epithelial cells. However, such high doses were delivered to only a few cells. CONCLUSION: The number of obstructed capillaries in human lungs is lower than in rat lungs; the distances between microspheres should be larger. Nevertheless, the individual doses absorbed by the pulmonary cells closest to the microspheres should be very important.

Complementarity of lung scintigraphy and D-dimer test in pulmonary embolism.

D-dimer assay (DDA), measuring fibrin degradation products, was compared with lung scintigraphy (LS) in a prospective unselected series of 83 consecutive patients referred owing to suspicion of pulmonary embolism (PE). This patient series was also used to compare several methods of performing and interpreting LS images. The final diagnosis was established independently by a separate panel with all available information except for the result of DDA. D-dimer was determined by ELISA (threshold value 500 ng/ml). LS, including perfusion (.Q) and pseudo-ventilation (Technegas) (.V), was classified according to PIOPED, (1) immediately by the physician on duty, and (2) retrospectively by a blinded panel. A positive (19) or negative (61) diagnosis of PE was achieved in 80 patients, the prevalence of PE being 24%. Only one false-negative was noted on DDA (sensitivity=95%) but there were 42 false-positives (specificity=31%), resulting in a positive predictive value of 30% and a negative predictive value of 95%. Emergency and retrospective interpretations of LS were close (kappa=0.4). In a minority of patients, PE may be excluded with reasonable certainty if DDA is normal, resulting in a significant saving in terms of time and money.

Auxiliary liver transplantation in patients with fulminant hepatic failure: hepatobiliary scintigraphic follow-up.

Auxiliary liver transplantation (ALT), retaining in place the liver of the recipient, has been proposed as an alternative to liver replacement in patients with fulminant hepatic failure (FHF). Hepatobiliary scintigraphy (HS) has proved a unique tool for the separate assessment of graft and native liver function. Forty-eight HS scans were performed, following the injection of technetium-99m trimethyl-bromo-imino-diacetic acid, in six patients who underwent ALT for FHF. Quantitative parameters were derived from the time-activity curves of both the graft and the native liver. The function of the graft remained normal as long as the patients remained under immunosuppressive therapy (IST). The function of the native liver was almost completely absent in the 1st month in five patients, but it improved gradually in four of them. IST was then decreased in four patients and finally withdrawn in three. Spontaneous graft atrophy occurred in two patients and the graft was removed in two. All of the patients in whom IST was reduced had a normal global hepatic function and selective uptake (RU) >30% at that time. In ALT patients with FHF, HS can distinguish non-invasively the functional performance of both the donor and the recipient liver and its evolution with time.

Incidence of dysthyroidism during interferon therapy in chronic hepatitis C.

Seventy-nine patients (40 males, 39 females) were enrolled in a prospective study of lymphoblastoid interferon-alpha (IFN), 3-5 MU three times weekly. They were randomly assigned to receive either 12 months of IFN therapy, or to 6 months of observation followed by 6 months of IFN therapy. The thyroid functional and immunological status was checked every other month during and after treatment. Before treatment, antithyroid antibodies were found in 6 patients (7.5%). Two were hypothyroid and were excluded from the study before starting IFN therapy. Seventy-seven patients received IFN therapy. Of these, thyroid abnormalities appeared in 6 (7.5%). Hyperthyroidism was observed in 3 patients. Two recovered within a few months, but 1 developed subsequent hypothyroidism. Hypothyroidism was observed in 2 patients. TSH blood values were persistently abnormal, but thyroid antibody levels remained increased and fluctuating. Thyroid function usually recovered within a few months; but 2 patients required hormonal therapy and 1 was treated with carbimazole. In 1 patient, a small thyroid papillary carcinoma was observed, but no evidence of relationship with the liver disease or with IFN therapy was found. In a patient with chronic hepatitis C, systematic thyroid assessment should be performed before initiating IFN therapy, including clinical examination, and measurement of TSH and anti-thyroperoxidase antibodies (TPO Ab). During treatment, a TSH assay every other month appears to be necessary and sufficient.

[Radiotherapy-induced cognitive dysfunction in 4-months-old male Wistar rats]]. / Dysfonctionnement cognitif radio-induit chez le rat Wistar mâle âgé de 4 mois.

PURPOSE: Behavioral dysfunction of memory process arising 4 months after whole brain irradiation (30 Gy/10 fractions/12 days) has been demonstrated in 16-27 month old rats, as compared with non irradiated rats. This study was therefore aimed at delivering the same irradiation in young rats and comparing results with those previously obtained in old rats. MATERIAL AND METHODS: Thirty-three 4-month old rats were included into the study. Eighteen received whole brain irradiation (30 Gy/10 fractions/12 days), and 18 were given sham irradiation. Sequential behavior studies were done before irradiation and during the 7 months following irradiation. RESULTS: Significant decrease in memory function was observed in irradiated rats 1 month (p < 0.001), 3 months (p < 0.013), and 6 months (p = 0.007) post-irradiation. This was accompanied by learning deficit 1 month (p = 0.01), 4.5 months (p = 0.03), and 7 months (p = 0.009) post-irradiation. CONCLUSION: Response to radiation therapy observed in young rats differed from that observed in old rats. Young rats showed earlier decrease in memory function than old rats, but this deficit was followed by partial recovery. Learning deficits also arised earlier in young rats than in old rats. In two cases this deficit was permanent.

Proportional anatomical stereotactic atlas for visual interpretation of brain SPET perfusion images.

A semi-automatic method was developed to determine the anterior (AC) and posterior (PC) commissures on brain single-photon emission tomographic (SPET) perfusion images, and then to draw the proportional anatomical Talairach's grid on each axial SPET image. First, the AC-PC line was defined on SPET images from the linear regression of four internal landmarks (frontal pole of the brain, inferior limit of the anterior corpus callosum, sub-thalamic point and occipital pole). Second, the SPET position of AC and PC points on the AC-PC line was automatically determined from measurements made on hard copies of magnetic resonance (MR) images of the patients. Finally, a proportional Talairach's grid was automatically drawn on each axial SPET image. To assess the accuracy of localization of AC and PC points, co-registered technetium-99m hexamethylpropylene amine oxime SPET and MR images from 11 subjects were used. The mean displacements between estimated points on SPET and true points on MRI (Deltax=sagittal, Deltay=frontal and Deltaz=axial displacement) were calculated. The mean displacements (in mm) were Deltax=-1.4+/-1.8, Deltay=-1.7+/-3.3 and Deltaz=-1. 1+/-2.5 for AC, and Deltax=-1.8+/-1.8, Deltay=0.3+/-3.2 and Deltaz=-1.3+/-2.7 for PC. These displacements represented an error of less than 5 mm at the anterior or posterior pole of the brain or at the vertex. Intra- and inter-observer comparisons did not reveal significant differences in mean displacements. Thus, this semi-automatic method results in reproducible and accurate stereotactic localization of SPET perfusion abnormalities. This method can be used routinely for repeat follow-up studies in the same subject as well as in different individuals without requiring SPET-MRI co-registration.

Nuclear medicine and cardiology: the position of the Union of European Medical Specialists/Section of Nuclear Medicine.

This paper summarizes a communication presented at the Second International Conference of Nuclear Cardiology, held in Cannes on 23-26 April 1995. The general evolution of nuclear medicine in Europe is examined within the context of European Union Directives, and the role of the Union of European Medical Specialists/Section of Nuclear Medicine is discussed. Thereafter consideration is given to the technical aspects of cardiovascular nuclear medicine procedures, and the situation with respect to such procedures in European countries is examined. In most European countries, nuclear medicine is a recognized specialty, while "nuclear cardiology" does not exist in its own right. In general, only nuclear medicine specialists have the responsibility for radionuclide studies, and most cardiovascular studies are performed under the direct responsibility of a licensed nuclear medicine specialist.