Nuclear medicine methods for evaluation of skeletal infection among other diagnostic modalities.

Skeletal infection continues to be a common and difficult condition in clinical practice and early accurate diagnosis is very challenging. Clinical and laboratory features of skeletal infections are not always present, may be confusing, and are nonspecific for bone infection in its early stages, therefore, several imaging modalities are used for early detection of osteomyelitis. Plain films should always be the first step in the imaging assessment of osteomyelitis, however, the sensitivity for X-ray radiography has been reported to range from 43% to 75%, and the specificity from 75% to 83%. Over years, scintigraphic procedures have become an essential part of the diagnostic procedure for osteomyelitis. The standard approach for bone scintigraphy with tech 99mTc labeled methylene diphosphonate to assess for osteomyelitis is to perform a three-phase procedure. The positive uptake on all three phases is highly sensitive for osteomyelitis (sensitivity 73% to 100%). 67Ga citrate gained more attention for the more specific diagnosis of osteomyelitis due to its known capacity to localize in cases of active infection and pus. The reported specificity for 67Ga scintigraphy in osteomyelitis is around 67-70% and the specificity is much higher (92%) when 67Ga single photon emission tomography was obtained. Labeled white blood cell (WBC) imaging has become the procedure of choice to diagnose most cases of skeletal infections except for those of the spine. Labeling of leucocytes can be done either by 111In or 99mTc labeled hexamethylpropylene amineoxime. The sensitivity and specificity for labeled WBCs are in the high range of 80% to 90%. [18F]fluorodeoxyglucose positron emission tomography (PET) has been found to accumulate non-specifically at sites of infection and inflammation. Investigational studies showed that PET is particularly valuable in the evaluation of chronic osteomyelitis and infected prostheses. Other imaging modalities include sonography, computed tomography (CT) and magnetic resonance imaging (MRI). The sensitivity and specificity of CT for the diagnosis of osteomyelitis has not been established clearly and are in the range of 65% to 75%. The sensitivity of MRI for osteomyelitis has been generally reported as being between 82% and 100%, and specificity between 75% and 96%. Cases of osteomyelitis commonly referred to diagnostic imaging departments include chronic osteomyelitis, diabetic foot infections, vertebral osteomyelitis, joint prostheses and patients with suspected reinfection. These specific entities need special attention and careful selection of the correct tracer or combination of imaging modalities that is best suited for the proper therapeutic management protocols.

Value of myocardial SPECT in early detection of ischaemia in children with sickle cell anaemia.

BACKGROUND: Cardiovascular complications of sickle cell anaemia (SCA) are relatively infrequent compared with other cerebral and skeletal insults. However, myocardial infarction and cardiac dysfunction have been reported in autopsied patients with SCA. When left ventricular functional parameters of gated SPECT and echocardiography were compared incidentally in children with SCA, some 26% of patients were found to have evident myocardial ischaemia. This stimulated the current work with the aim to further analyse these incidental findings and evaluate the possible role of SPECT in early detection of coronary insufficiency in children with SCA. PATIENTS AND METHODS: Twenty-seven patients (19 girls, 8 boys), mean age 9.2±4.2 years, with SCA were examined by baseline ECG, echocardiography and gated SPECT. They were all free from any cardiac symptoms. Intravenous injection of 5 to 10 mCi 99MTc-MIBI or 99MTc-Myoview was administered, according to the predetermined weight-dependent paediatric dose. Stress SPECT was obtained 45 to 60 minutes after tracer injection, which took place at peak physical exercise (6 patients) or 3 to 4 minutes after IV infusion of dipyridamole pharmacological stress (21 patients). Rest SPECT study was acquired 4 to 5 hours later after a second injection of 99MTc-MIBI/Myoview. A semiquantitative nine-segment stress/rest bull's eye model was used to assess to the presence/extent of myocardial ischaemia. RESULTS: Myocardial perfusion was normal in 20 patients (74%). Seven patients (26%) had significant perfusion defects in the stress images. Four of them showed perfusion defect in one or two segments. Complete reversibility in the rest study was seen in all patients. Two patients showed a mixture of reversible and fixed perfusion defects in four segments. One patient had evident left ventricular dilatation with multiple fixed and reversible defects (cardiomyopathy). In this case, a diffusely reduced myocardial wall contractility was seen and a low LVEF of 42% as assessed by echocardiography. This was the only case showing agreement between the echo and SPECT findings. In the whole cohort the EF% and FS% by echocardiography were 61.7±5.9% and 33.2±3.4% respectively (mean±SD). There were no significant relations between myocardial perfusion abnormalities when compared with EF% and FS%; (p>0.05). CONCLUSION: Cardiac involvement in the form of myocardial ischaemia should be regarded as a high-risk complication in patients with SCA. Myocardial perfusion scintigraphy succeeded in the early detection of myocardial perfusion abnormalities in patients with SCA.

Radiation exposure and dosimetry in transplant patients due to nuclear medicine studies.

Organ transplantation is now an accepted method of therapy for treating patients with end stage failure of kidneys, liver, heart or lung. Nuclear Medicine may provide functional data and semi-quantitative parameters. However, one serious factor that hampers the use of nuclear medicine procedures in transplant patients is the general clinical concern about radiation exposure to the patient. This leads us to discuss the effective doses and radiation dosimetry associated with radionuclide procedures used in the management and follow-up of transplant patients. A simple way to place the risk associated with Nuclear Medicine studies in an appropriate context is to compare the dose with that received from a more familiar source of exposure such as from a diagnostic X-ray procedure. The radiation dose for the different radiopharmaceuticals used to study transplant organ function ranges between 0.1 and 5.3 mSv which is comparable to X-ray procedures with the exception of 201Tl and 111In-antimyosin. Thus Nuclear Medicine studies do not bear a higher radiation risk than the often used X-ray studies in transplant patients.

Aspects of fetal thyroid dose following iodine-131 administration during early stages of pregnancy in patients suffering from benign thyroid disorders.

Detrimental effects on the thyroid of the developing fetus as a result of iodine-131 treatment for thyrotoxicosis of the mother in the first trimester of pregnancy are discussed. Dose estimations under typical clinical circumstances yield a fetal thyroid dose of 100- 450 Sv. This dose may increase considerably if the blood concentration of (131)I in the mother remains high. Under such circumstances there may be fetal thyroid dysfunction, which can lead to severe abnormalities.

Renographic indices for evaluation of changes in graft function.

Radionuclide renal diagnostic studies play an important role in assessing renal allograft function, especially in the early post-transplant period. In the past two decades various quantitative parameters have been derived from the radionuclide renogram to evaluate changes in perfusion and/or function of the kidney allograft. In this review article we discuss the quantitative parameters that have been used to assess graft condition, with emphasis on the early postoperative period. These quantitative methods are divided into parameters used for assessing renal graft perfusion and parameters used for evaluating parenchymal function. The blood flow in renal transplants can be quantified (a) by measuring the rate of activity appearance in the kidney graft, (b) by calculating the ratio of the integral activity under the transplanted kidney and arterial curves and (c) by calculating the renal vascular transit time. In this article we review a number of parenchymal uptake and excretion indices, such as the accumulation index, the graft uptake capacity at 2 and 10 min, the excretion index and the elimination index. The literature on these parameters shows that they have some practical disadvantages. In addition, values suffer from significant overlap when various graft pathologies coexist. A retrospective study was designed in our institution to evaluate the clinical usefulness of some of the frequently used previously published methods in which the graft function is quantitatively assessed in the early post-transplant period. The quantitative parameters studied which were reasonably reproducible in our hands included: global perfusion index (GPI), cortical perfusion index (CPI), vascular transit time, and the parenchymal parameters uptake capacity at 2 min (UC2) and elimination index (K3/20). The patient population in this study consisted of 43 patients with 157 technetium-99m mercaptylacetyltriglycine renograms. The perfusion indices GPI and CPI did not allow differentiation of the acute tubular necrosis (ATN) group from the acute rejection (AR) group; however, they were of value in monitoring the improvement in the condition of the graft dysfunction in both the AR and ATN groups. As for the parenchymal parameters, both UC2 and K3/20 were able to differentiate stable graft function (SGF) versus AR and ATN groups but were unable to separate AR from ATN dysfunction. The ability of these parenchymal parameters to detect improvement in the graft function was poor and statistically non-significant. From the literature data and our own findings it is concluded that radionuclide scintigraphy of renal transplants has assumed an important role, especially if performed serially, in monitoring graft function in the post-transplant period. Many quantitative parameters have been derived from the radionuclide renogram to evaluate changes in perfusion and/or function of the kidney allograft. It appears that these quantitative numerical values are unable to differentiate unequivocally between grafts with ATN and AR cases. The real value of these parameters lies in the follow-up of the dysfunction processes, which helps the clinician to determine the appropriate therapeutic regimen.

Quantitative scintigraphic parameters for the assessment of renal transplant patients.

Radionuclide renal diagnostic studies play an important role in assessing renal allograft function especially in the early post transplant period. In the last two decades various quantitative parameters have been derived from the radionuclide renogram to facilitate and confirm the changes in perfusion and/or function of the kidney allograft. In this review article we discuss the quantitative parameters that have been used to assess graft condition with emphasis on the early post-operative period. These quantitative methods were divided into parameters used for assessing renal graft perfusion and parameters used for evaluating parenchymal function. The blood flow in renal transplants can be quantified by measuring (a) the rate of activity appearance in the kidney graft; (b) the ratio of the integral activity under the transplanted kidney and arterial curves e.g. Hilson's perfusion index and Kircher's kidney/aortic ratio; (c) calculating the renal vascular transit time by deconvolution analysis. The literature overview on these parameters showed us that they have some practical disadvantages of requiring high quality bolus injection and numerical variations related to changes in the site and size of regions of interest. In addition, the perfusion parameter values suffer from significant overlap when various graft pathologies coexist. Quantitative evaluation of the graft parenchymal extraction and excretion was assessed by parameters derived from 123I/131I-OIH, 99mTc-DTPA or 99mTc-MAG3 renograms. We review in this article a number of parenchymal parameters which include (1) plasma clearance methods like glomerular filtration rate (GFR) and effective renal plasma flow (ERPF); (2) renal transit times such as parenchymal mean transit time, Tmax, T1/2; (3) parenchymal uptake and excretion indices as the accumulation index, graft uptake capacity at 2 and 10 min, excretion index and elimination index. These indices, however, are non-specific and far from defining a specific cause for graft parenchymal dysfunction. In conclusion, despite that the literature is replete with mathematical strategies for quantitating perfusion and parenchymal functions, none of these have enough diagnostic power for specific diagnosis of graft dysfunction. In addition, no universal agreement on the use of certain quantitation parameters in transplant patients has been reached.

Diagnostic imaging modalities for delayed renal graft function: a review.

A varying percentage of cadaveric transplant recipients remain anuric or oliguric and depend on dialysis in the first weeks after transplantation. This delayed graft function group needs careful management to detect additional post-transplant events. Under these clinical circumstances, the assessment of allograft status depends to a great extent on non-invasive imaging studies. The wide variety of imaging procedures for the transplanted kidney, combined with recent technical advances in ultrasonography, scintigraphy and radiopharmaceuticals, computed tomography and magnetic resonance imaging, has created a challenging and sometimes confusing environment for clinicians, radiologists and nuclear medicine physicians. Assessing the relative merits of available procedures and choosing an optimal approach to the clinical presentation of a particular graft is sometimes difficult. The contrasting characteristics of these diagnostic methods led us to consider their relative roles and to determine their selective use. This review focuses on the value and limitations of diagnostic imaging modalities in the management of patients with impaired or delayed graft function. Our emphasis is on ultrasonography and nuclear medicine, as these are the most frequently used methods.