Trends in Use of Medical Imaging in US Health Care Systems and in Ontario, Canada, 2000-2016

Importance

Medical imaging increased rapidly from 2000 to 2006, but trends in recent years have not been analyzed.

Objective

To evaluate recent trends in medical imaging.

Design, Setting, and Participants

Retrospective cohort study of patterns of medical imaging between 2000 and 2016 among 16 million to 21 million patients enrolled annually in 7 US integrated and mixed-model insurance health care systems and for individuals receiving care in Ontario, Canada.

Exposures

Calendar year and country (United States vs Canada).

Main Outcomes and Measures

Use of computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, and nuclear medicine imaging. Annual and relative imaging rates by imaging modality, country, and age (children [<18 years], adults [18-64 years], and older adults [≥65 years]).

Results

Overall, 135 774 532 imaging examinations were included; 5 439 874 (4%) in children, 89 635 312 (66%) in adults, and 40 699 346 (30%) in older adults. Among adults and older adults, imaging rates were significantly higher in 2016 vs 2000 for all imaging modalities other than nuclear medicine. For example, among older adults, CT imaging rates were 428 per 1000 person-years in 2016 vs 204 per 1000 in 2000 in US health care systems and 409 per 1000 vs 161 per 1000 in Ontario; for MRI, 139 per 1000 vs 62 per 1000 in the United States and 89 per 1000 vs 13 per 1000 in Ontario; and for ultrasound, 495 per 1000 vs 324 per 1000 in the United States and 580 per 1000 vs 332 per 1000 in Ontario. Annual growth in imaging rates among US adults and older adults slowed over time for CT (from an 11.6% annual percentage increase among adults and 9.5% among older adults in 2000-2006 to 3.7% among adults in 2013-2016 and 5.2% among older adults in 2014-2016) and for MRI (from 11.4% in 2000-2004 in adults and 11.3% in 2000-2005 in older adults to 1.3% in 2007-2016 in adults and 2.2% in 2005-2016 in older adults). Patterns in Ontario were similar. Among children, annual growth for CT stabilized or declined (United States: from 10.1% in 2000-2005 to 0.8% in 2013-2016; Ontario: from 3.3% in 2000-2006 to -5.3% in 2006-2016), but patterns for MRI were similar to adults. Changes in annual growth in ultrasound were smaller among adults and children in the United States and Ontario compared with CT and MRI. Nuclear medicine imaging declined in adults and children after 2006.

Conclusions and Relevance

From 2000 to 2016 in 7 US integrated and mixed-model health care systems and in Ontario, rates of CT and MRI use continued to increase among adults, but at a slower pace in more recent years. In children, imaging rates continued to increase except for CT, which stabilized or declined in more recent periods. Whether the observed imaging utilization was appropriate or was associated with improved patient outcomes is unknown.

Current use and future potential of organometallic radiopharmaceuticals

Contrary to common belief, organometallic compounds exhibit remarkable stability in aerobic and even diluted aqueous solutions. Technetium-sestamibi (Cardiolite) is one of the most prominent examples of this class of compounds routinely used in nuclear medicine. This review summarises the recent progress in labelling of biomolecules with organometallic complexes for diagnostic and therapeutic application in radiopharmacy and exemplifies in detail developments focussing on organometallic technetium- and rhenium-tricarbonyl technologies. The value of such technologies has been recognised and they have become a valuable alternative to common labelling methodologies. An increasing number of groups have started to employ an organometallic precursor for the purpose of radioactive labelling of various classes of biomolecules, and the advantages and limitations of this new technique are compared with those of other labelling methods. The synthetic access to appropriate precursors via double-ligand exchange or aqueous carbonyl kit preparation for routine application is described. Strategies and examples for the design of appropriate bifunctional chelating agents for the Tc/Re-tricarbonyl core are given. The functionalization of biomolecules such as tracers for the central nervous system (dopaminergic and serotonergic), tumour affine peptides (somatostatin receptors, neuroreceptors) and tumour binding single-chain antibody fragments is summarised. Where possible and appropriate, the in vitro and in vivo results in respect of these examples are compared with those obtained with classical (99m)Tc/(188)Re(V)- and (111)In-labelled analogues. The preclinical results show the in many ways superior characteristics of organometallic labelling techniques.

Noninvasive in vivo measurement of vascular inflammation with F-18 fluorodeoxyglucose positron emission tomography

BACKGROUND

Fluorine 18 fluorodeoxyglucose (FDG) has been shown to accumulate in inflamed tissues. However, it is not known whether vascular inflammation can be measured noninvasively. The aim of this study was to test the hypothesis that vascular inflammation can be measured noninvasively by use of positron emission tomography (PET) with FDG.

METHODS AND RESULTS

Inflamed atherosclerotic lesions were induced in 9 male New Zealand white rabbits via balloon injury of the aortoiliac arterial segment and exposure to a high cholesterol diet. Ten rabbits fed standard chow served as controls. Three to six months after balloon injury, the rabbits were injected with FDG (1 mCi/kg), after which aortic uptake of FDG was assessed (3 hours after injection). Biodistribution of FDG activity within aortic segments was obtained by use of standard well gamma counting. FDG uptake was also determined noninvasively in a subset of 6 live atherosclerotic rabbits and 5 normal rabbits, via PET imaging and measurement of standardized uptake values over the abdominal aorta. Plaque macrophage density and smooth muscle cell density were determined by planimetric analysis of RAM-11 and smooth muscle actin staining, respectively. Biodistribution of FDG within nontarget organs was similar between atherosclerotic and control rabbits. However, well counter measurements of FDG uptake were significantly higher within atherosclerotic aortas compared with control aortas (P < .001). Within the upper abdominal aorta of the atherosclerotic group (area of greatest plaque formation), there was an approximately 19-fold increase in FDG uptake compared with controls (108.9 +/- 55.6 percent injected dose [%ID]/g x 10(3) vs 5.7 +/- 1.2 %ID/g x 10(3) [mean +/- SEM], P < .001). In parallel with these findings, FDG uptake, as determined by PET, was higher in atherosclerotic aortas (standardized uptake value for atherosclerotic aortas vs control aortas, 0.68 +/- 0.06 vs 0.13 +/- 0.01; P < .001). Moreover, macrophage density, assessed histologically, correlated with noninvasive (PET) measurements of FDG uptake (r = 0.93, P < .0001). In contrast to this finding, FDG uptake did not correlate with either aortic wall thickness or smooth muscle cell staining of the specimens.

CONCLUSION

These data show that FDG accumulates in macrophage-rich atherosclerotic plaques and demonstrate that vascular macrophage activity can be quantified noninvasively with FDG-PET. As such, measurement of vascular FDG uptake with PET holds promise for the noninvasive characterization of vascular inflammation.

New directions in the coordination chemistry of 99mTc: a reflection on technetium core structures and a strategy for new chelate design

Bifunctional chelates offer a general approach for the linking of radioactive metal cations to macromolecules. In the specific case of 99mTc, a variety of technologies have been developed for assembling a metal-chelate-biomolecule complex. An evaluation of these methodologies requires an appreciation of the coordination characteristics and preferences of the technetium core structures and oxidation states, which serve as platforms for the development of the imaging agent. Three technologies, namely, the MAG3-based bifunctional chelates, the N-oxysuccinimidylhydrazino-nicotinamide system and the recently described single amino acid chelates for the {Tc(CO)3}1+ core, are discussed in terms of the fundamental coordination chemistry of the technetium core structures. In assessing the advantages and disadvantages of these technologies, we conclude that the single amino acid analogue chelates (SAAC), which are readily conjugated to small peptides by solid-phase synthesis methods and which form robust complexes with the {Tc(CO)3}1+ core, offer an effective alternative to the previously described methods.

Apoptosis-detecting radioligands: current state of the art and future perspectives

This review provides a critical and thorough overview of the radiopharmaceutical development and in vivo evaluation of all apoptosis-detecting radioligands that have emerged so far, along with their possible applications in nuclear medicine. The following SPECT and PET radioligands are discussed: all forms of halogenated Annexin V (i.e. (123)I-labelled, (124)I-labelled, (125)I-labelled, (18)F-labelled), (99m)Tc/(94m)Tc-labelled Annexin V derivatives using different chelators and co-ligands (i.e. BTAP, Hynic, iminothiolane, MAG(3), EDDA, EC, tricarbonyl, SDH) or direct (99m)Tc-labelling, (99m)Tc-labelled Annexin V mutants and (99m)Tc/(18)F-radiopeptide constructs (i.e. AFIM molecules), (111)In-DTPA-PEG-Annexin V, (11)C-Annexin V and (64)Cu-, (67)Ga- and (68)Ga-DOTA-Annexin V. In addition, the potential role and clinical relevance of anti-PS monoclonal antibodies and other alternative apoptosis markers are reviewed, including: anti-Annexin V monoclonal antibodies, radiolabelled caspase inhibitors and substrates and mitochondrial membrane permeability targeting radioligands. Nevertheless, major emphasis is placed on the group of Annexin V-based radioligands, in particular (99m)Tc-Hynic-Annexin V, since this molecule is by far the most extensively investigated and best-characterised apoptosis marker at present. Furthermore, the newly emerging imaging modalities for in vivo detection of programmed cell death, such as MRI, MRS, optical, bioluminescent and ultrasound imaging, are briefly described. Finally, some future perspectives are presented with the aim of promoting the development of potential new strategies in pursuit of the ideal cell death-detecting radioligand.

Diagnostic performance of imaging investigations in detecting and differentiating cardiac amyloidosis: a systematic review and meta-analysis

AIMS

The study aims to systematically assess the diagnostic performance of cardiac magnetic resonance (CMR) and nuclear scintigraphy (index tests) for the diagnosis and differentiation of subtypes of cardiac amyloidosis.

METHODS AND RESULTS

MEDLINE and Embase electronic databases were searched for studies evaluating the diagnostic performance of CMR or nuclear scintigraphy in detecting cardiac amyloidosis and subsequently in differentiating transthyretin amyloidosis (ATTR) from immunoglobulin light-chain (AL) amyloidosis. In this meta-analysis, histopathological examination of tissue from endomyocardial biopsy (EMB) or extra-cardiac organs were reference standards. Pooled sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio were calculated, and a random effects meta-analysis was used to estimate diagnostic odds ratios. Methodological quality was assessed using a validated instrument. Of the 2947 studies identified, 27 met the criteria for inclusion. Sensitivity and specificity of CMR in diagnosing cardiac amyloidosis was 85.7% and 92.0% against EMB reference and 78.9% and 93.9% with any organ histology reference. Corresponding sensitivity and specificity of nuclear scintigraphy was 88.4% and 87.2% against EMB reference and 82.0% and 98.8% with histology from any organ. CMR was unable to reliably differentiate ATTR from AL amyloidosis (sensitivity 28.1-99.0% and specificity 11.0-60.0%). Sensitivity and specificity of nuclear scintigraphy in the differentiation of ATTR from AL amyloidosis ranged from 90.9% to 91.5% and from 88.6% to 97.1%. Pooled negative likelihood ratio and positive likelihood ratio for scintigraphy in this setting were 0.1 and 8, with EMB reference standard. Study quality assessed by QUADAS-2 was generally poor with evidence of bias.

CONCLUSIONS

Cardiac magnetic resonance is a useful test for diagnosing cardiac amyloidosis but is not reliable in further classifying the disease. Nuclear scintigraphy offers strong diagnostic performance in both the detection of cardiac amyloidosis and differentiating ATTR from AL amyloidosis. Our findings support the use of both imaging modalities in a non-invasive diagnostic algorithm that also tests for the presence of monoclonal protein.

The use of nuclear medicine in infections

The spectrum of infectious diseases has changed over the last few years, hence the requirements for radionuclide imaging for the detection of infection are becoming more demanding so that, although gallium-67 and labelled leucocytes remain useful agents, there is currently great interest in the development of new agents especially able to target chronic, non-pyogenic inflammation. Agents can be classified according to the site at which the radiolabel is targeted: pre-endothelial (for example, labelled leucocytes), endothelial (for example, labelled anti-endothelial monoclonal antibodies) or post-endothelial (for example, fluorine-18-fluorodeoxyglucose (FDG)). 67Ga and labelled polyclonal human immunoglobulin (HIG) localize at inflammation initially as a result of increased endothelial permeability, followed by retention of the label through binding to local extravascular receptors. Labelled leucocytes are avidly taken up by acute pyogenic inflammatory foci but perform less well in chronic inflammation. Other indications for labelled leucocytes include bone infection and undiagnosed fever. Nevertheless, since many causes of the latter do not stimulate a neutrophilic infiltrate, a non-specific agent, such as 67Ga, FDG or HIG, may be preferable, especially in patients with no immediate significant medical history. Since endothelial E-selectin expression is closely correlated to lymphocyte migration, labelled anti-E-selectin monoclonal antibody may also have a potential role for imaging chronic inflammation.

Comparison of recent utilization trends in radionuclide myocardial perfusion imaging among radiologists and cardiologists

PURPOSE

To study recent practice patterns in radionuclide myocardial perfusion imaging (MPI) and related procedures among radiologists, cardiologists, and other physicians.

METHODS AND MATERIALS

The nationwide Medicare administrative Part B claims summary databases from 1998 and 2002 were used to assess utilization rate changes in the 4 primary procedure codes for MPI, the seven codes for diagnostic cardiac catheterization with coronary angiography, and the single code for stress echocardiography. Rate changes among radiologists, cardiologists, and other physicians were determined for the total Medicare population, as well as for the 3 primary places of service at which imaging is formed: hospital inpatient facilities, hospital outpatient facilities, and private offices. Ratios of the use of the 2 supplementary codes for left ventricular (LV) wall motion and ejection fraction to that of the primary MPI codes were calculated for 2002.

RESULTS

The utilization rate per 1000 Medicare beneficiaries of MPI rose among radiologists from 19.8 in 1998 to 20.1 in 2002, a 2% increase. The rate among cardiologists rose from 22.9 in 1998 to 40.7 in 2002, a 78% increase. Most of this growth occurred in cardiologists' offices, where the utilization rate increased 101% over the 4 years. In 2002, the ratios of the use of the supplementary LV wall motion and ejection fraction codes to that of the primary MPI codes were 1.73 for cardiologists and 1.46 among radiologists. Between 1998 and 2002, the utilization of diagnostic cardiac catheterization among cardiologists increased by 19%, and their utilization of stress echocardiography increased by 21%.

CONCLUSION

In recent years within the Medicare population, the rate of utilization of MPI among radiologists has remained relatively stable, whereas it has risen sharply among cardiologists. The greatest growth was seen in cardiologists' private offices. This raises concerns about possible inappropriate utilization of MPI and also about the potential effect self-referral has on this utilization trend. The increased use of MPI by cardiologists did not result in reduction in their use of either cardiac catheterization with coronary angiography or stress echocardiography.

Novel iodinated tracers, MIBG and BMIPP, for nuclear cardiology

With the rapid growth of molecular biology, in vivo imaging of such molecular process (i.e., molecular imaging) has been well developed. The molecular imaging has been focused on justifying advanced treatments and for assessing the treatment effects. Most of molecular imaging has been developed using PET camera and suitable PET radiopharmaceuticals. However, this technique cannot be widely available and we need alternative approach. ¹²³I-labeled compounds have been also suitable for molecular imaging using single-photon computed tomography (SPECT) ¹²³I-labeled meta-iodobenzylguanidine (MIBG) has been used for assessing severity of heart failure and prognosis. In addition, it has a potential role to predict fatal arrhythmia, particularly for those who had and are planned to receive implantable cardioverter-defibrillator treatment. ¹²³I-beta-methyl-iodophenylpentadecanoic acid (BMIPP) plays an important role for identifying ischemia at rest, based on the unique capability to represent persistent metabolic alteration after recovery of ischemia, so called ischemic memory. Since BMIPP abnormalities may represent severe ischemia or jeopardized myocardium, it may permit risk analysis in CAD patients, particularly for those with chronic kidney disease and/or hemodialysis patients. This review will discuss about recent development of these important iodinated compounds.

Principles and controversies in lymphoscintigraphy with emphasis on breast cancer

The concept of the sentinel node lay fallow until lymph node mapping was developed. This article provides a brief history of the sentinel lymph node concept, discusses reproducibility, radiopharmaceuticals, equipment, techniques, and radiation safety, and addresses metastasis in breast cancer and controversies in breast lymphoscintigraphy.

Contemporary adrenal scintigraphy

INTRODUCTION

High-resolution computed tomography (CT) and magnetic resonance (MR) imaging have replaced scintigraphy as primary imaging modalities for the evaluation of adrenal diseases.

DISCUSSION

Thin-slice CT, CT contrast washout studies and MR pulse sequences specifically designed to identify adrenal lipid content have radically changed the approach to anatomic imaging and provide unique insight into the physical characteristics of the adrenals. With a confirmed biochemical diagnosis, further evaluation is often unnecessary, especially in diagnostic localization of diseases of the adrenal cortex. However, despite the exquisite detail afforded by anatomy-based imaging, there are not infrequently clinical situations in which the functional insight provided by scintigraphy is crucial to identify adrenal dysfunction and to assist in localization of adrenocortical and adrenomedullary disease. The introduction of hybrid PET/CT and SPECT/CT, modalities that directly integrate anatomic and functional information, redefine the radiotracer principle in the larger context of high-resolution anatomic imaging. Instead of becoming obsolete, scintigraphy is an element of a device that combines it with CT or MR to allow a direct correlation between function and anatomy, whereby the combination creates a more powerful diagnostic tool than the separate component modalities.

Rationale for the use of radiolabelled peptides in diagnosis and therapy

Nuclear medicine techniques are becoming more important in imaging oncological and infectious diseases. For metabolic imaging of these diseases, antibody and peptide imaging are currently used. In recent years peptide imaging has become important, therefore the rationale for the use of peptide imaging is described in this article. Criteria for a successful peptide tracer are a high target specificity, a high binding affinity, a long metabolic stability and a high target-to-background ratio. Tracer internalization is also beneficial. For oncological imaging, many tracers are available, most originating from regulatory peptides, but penetrating peptides are also being developed. Peptides for imaging inflammatory and infectious diseases include regulatory peptides, antimicrobial peptides and others. In conclusion, for the imaging of oncological, imflammatory and infectious diseases, many promising peptides are being developed. The ideal peptide probe is characterized by rapid and specific target localization and binding with a high tumour-to-background ratio.

Nanobodies for Medical Imaging: About Ready for Prime Time?

Recent advances in medical treatments have been revolutionary in shaping the management and treatment landscape of patients, notably cancer patients. Over the last decade, patients with diverse forms of locally advanced or metastatic cancer, such as melanoma, lung cancers, and many blood-borne malignancies, have seen their life expectancies increasing significantly. Notwithstanding these encouraging results, the present-day struggle with these treatments concerns patients who remain largely unresponsive, as well as those who experience severely toxic side effects. Gaining deeper insight into the cellular and molecular mechanisms underlying these variable responses will bring us closer to developing more effective therapeutics. To assess these mechanisms, non-invasive imaging techniques provide valuable whole-body information with precise targeting. An example of such is immuno-PET (Positron Emission Tomography), which employs radiolabeled antibodies to detect specific molecules of interest. Nanobodies, as the smallest derived antibody fragments, boast ideal characteristics for this purpose and have thus been used extensively in preclinical models and, more recently, in clinical early-stage studies as well. Their merit stems from their high affinity and specificity towards a target, among other factors. Furthermore, their small size (~14 kDa) allows them to easily disperse through the bloodstream and reach tissues in a reliable and uniform manner. In this review, we will discuss the powerful imaging potential of nanobodies, primarily through the lens of imaging malignant tumors but also touching upon their capability to image a broader variety of nonmalignant diseases.

Targeting the vulnerable plaque: the evolving role of nuclear imaging

The majority of acute ischemic events relating to atherosclerosis are caused by plaque rupture and ensuing thrombosis. The risk of plaque rupture is dictated in part by plaque morphology, which in turn is influenced by pathophysiologic mechanisms at the cellular and molecular level. Anatomic imaging modalities such as intravascular ultrasound, high-resolution magnetic resonance imaging, and multislice computed tomography can identify morphologic features of the vulnerable plaque, such as a large lipid core and thin fibrous cap, but give little or no information regarding molecular and cellular mechanisms, such as endothelial function, macrophage activation, lipid transport and metabolism, and cell death. Recent studies suggest that nuclear imaging may be able to provide images of sufficient quality to identify and quantify some of these molecular and cellular pathophysiologic processes. In the future this could allow for the early identification and noninvasive monitoring of vulnerable plaque.

Is there life after technetium: what is the potential for developing new broad-based radionuclides?

The use of radionuclides for medical and for a multitude of other basic research applications has continued to grow at a very rapid pace. Procedures, based on their use as radiotracers for nuclear medicine imaging and for radiotherapy of cancer and other pathology, have become firmly established as important clinical modalities. It is estimated that on an annual basis in the United States alone, radionuclides are used medically in over 13 million imaging procedures, in over 100 million laboratory tests, and in an ever increasing number (> 100,000) for therapeutic administrations. One out of every four hospital patients undergoes a procedure that involves the use of radionuclides. Diagnostic imaging methods using planar/single-photon emission computed tomography and positron-emission tomography (PET) imaging, as well as the measurement of in vivo organ function, physiology, or biochemistry, have become indispensable tools in patient workup and management. More than 80% of all imaging studies (mostly anatomic) currently use technetium-99m (99mTc), because it has turned out to be the ideal isotope from various considerations. However, over the past few years, nuclear medicine has experienced a slow but steady evolution towards functional studies, quantitative PET imaging, and novel therapeutic approaches. New radionuclides are required for these applications, and their development has attracted considerable interest. This article reviews the current status and future prospects for the development of many new potential isotopes. Practical issues, such as the feasibility of large-scale production and wide-spread availability in a continuous reliable fashion, are addressed. To date, the data are not sufficient to answer the question as to whether any of these radionuclides (or their applications, for that matter) will eventually assume as broad-based a role as that of 99mTc. Nonetheless, there are a number of promising radionuclides that could assume an important place in the future practice of nuclear medicine.

GEP-NETS update: functional localisation and scintigraphy in neuroendocrine tumours of the gastrointestinal tract and pancreas (GEP-NETs)

For patients with neuroendocrine tumours (NETs) of the gastrointestinal tract and pancreas (GEP) (GEP-NETs), excellent care should ideally be provided by a multidisciplinary team of skilled health care professionals. In these patients, a combination of nuclear medicine imaging and conventional radiological imaging techniques is usually mandatory for primary tumour visualisation, tumour staging and evaluation of treatment. In specific cases, as in patients with occult insulinomas, sampling procedures can provide a clue as to where to localise the insulin-hypersecreting pancreatic NETs. Recent developments in these fields have led to an increase in the detection rate of primary GEP-NETs and their metastatic deposits. Radiopharmaceuticals targeted at specific tumour cell properties and processes can be used to provide sensitive and specific whole-body imaging. Functional imaging also allows for patient selection for receptor-based therapies and prediction of the efficacy of such therapies. Positron emission tomography/computed tomography (CT) and single-photon emission CT/CT are used to map functional images with anatomical localisations. As a result, tumour imaging and tumour follow-up strategies can be optimised for every individual GEP-NET patient. In some cases, functional imaging might give indications with regard to future tumour behaviour and prognosis.

Antisense imaging: where are we now?

The field of antisense targeting is changing rapidly as additional results from in vitro studies and animal and patient trials become available. While these developments apply primarily to antisense chemotherapy, many have implications for antisense imaging and radiotherapy. It may now be profitable to reconsider antisense imaging in the light of these recent developments. With the benefit of further insight, it may be possible to predict which antisense mechanisms will be preferable for antisense imaging. It is also possible to consider the influences of carriers (vectors) on the targeting of antisense DNA and whether this might improve imaging. Furthermore, estimates showing only low mRNA steady-state copy numbers per cell may be reconsidered in refining predictions of tissue counting rates. Finally, recent results suggest that radiolabeling antisense DNAs may not adversely influence the targeting properties of antisense DNAs.

Nuclear cardiology in the UK: activity and practice 1997

A questionnaire was sent to 251 nuclear medicine centres asking for details of nuclear medicine activity, and nuclear cardiology activity and practice in 1997. One hundred and seventy-one (68%) centres replied. Nuclear medicine activity was estimated at 11.8 studies/1,000 population/year, and 9.5% of these studies were within cardiology (1.12 studies/1,000/year). Myocardial perfusion imaging (MPI) studies accounted for 77% and radionuclide ventriculography (RNV) for 22% of all nuclear cardiology. On a national basis this represents activity levels of 0.86 and 0.25 studies/1,000/year for MPI and RNV, respectively. Of the 171 responding centres, 102 (60%) performed MPI studies and 81 (79%) of these reported that activity was increasing. However, MPI activity was unevenly distributed between hospitals. Two centres accounted for 13% of total MPI; others had far lower activity rates, and 51/102 (50%) centres performed less than 200 MPI studies/year. Comparison with previous surveys showed that nuclear medicine activity had almost doubled since 1990 (it was 6.0 studies/1,000 population in 1990, 9.3 studies/1,000 in 1994 and 11.8 studies/1,000 in 1997). Over the same period, nuclear cardiology activity had also risen, the greatest increase being seen for the last 3 years (it was 0.7 studies/1,000 population in 1990, 0.82 studies/1,000 in 1994 and 1.12 studies/1,000 in 1997). Despite these encouraging figures, MPI activity for 1997 remained well below that recommended by the British Cardiac Society in 1994 (2.6 studies/1,000/year) as adequate to serve the needs of patients with cardiac disease in the UK; it was also below the European average activity for the same year (2.2 studies/1,000/year). The anticipated increased workload for nuclear cardiology is encouraging despite the wide and varied practice of nuclear cardiology around the UK. The nuclear medicine community now needs to address the issues that will prevent it keeping up with demand, such as restricted camera time, excessive waiting lists and outdated equipment, but also to standardise acquisition and reporting techniques so that all studies, wherever performed, will be of a uniformly high standard.