Thyroid imaging.

Four modalities are being used to image the thyroid gland: (1) scintigraphy ("scanning"), employing one of several currently available radiopharmaceuticals, (2) ultrasound (US), (3) computed tomography (CT, "CAT" scan), and (4) magnetic resonance imaging (MRI). The first method, scintigraphy, provides an image of the spatial distribution of thyroid functional attributes, the nature of which are dependent on the interaction between the particular radiopharmaceutical employed and the tissue in question, whereas the latter three modalities provide an image of the spatial distribution of structural attributes such as the varying degrees of echogenicity of the tissues examined or the differential tissue attenuation of an x-ray beam, which permits visualization of the structures. A fifth modality, fluorescent thyroid scanning, in which fluorescence of the iodide within the thyroid gland is induced by low-dose external radiation and which gives an image of iodine distribution, is generally unavailable and only rarely used. For most patients, the combination of careful history, skilled physical examination, tests of thyroid function (and serum thyroglobulin and calcitonin for cancer evaluation), fine needle aspiration biopsy, and scintigraphy provide the most cost-effective means of evaluating the thyroid gland and its diseases. Of the four modalities currently used to image the thyroid gland--scintigraphy, ultrasound, computerized tomography, and magnetic resonance imaging--only scintigraphy has the widest application. It is employed to determine gland size, locate thyroid tissue, evaluate nodules and masses, determine the cause of a painful tender gland, differentiate various forms of goiter, detect differentiated thyroid carcinoma and gland remnants, assess suppressibility or stimulatability of the gland, and identify nonfunctioning cancers. Ultrasonography, computed tomography, and magnetic resonance imaging are not useful in differentiating between benign and malignant nodules, and their sensitivity in detecting impalpable nodules is not clinically useful, because nodules less than 1 to 1.5 cm in diameter are only rarely clinically significant. These modalities have limited utility in the evaluation of the thyroid gland: they are useful in sizing known lesions and for the detection of cervical lymphadenopathy in thyroid cancer cases.

Spinal-cerebrospinal fluid leak demonstrated by radiopharmaceutical cisternography.

Cerebrospinal fluid (CSF) leaks are known to occur under several conditions: lumbar puncture performed for contrast myelography, spinal surgery, spinal stab wounds, fracture of the thoracic spine, inadvertent spinal puncture during epidural anesthesia, traumatic lumbar meningocele, and bronchopleural subarachnoid fistula due to bronchogenic carcinoma. Spontaneous spinal leaks are uncommonly encountered in neurosurgical practice, but they are increasingly recognized as a cause of spontaneous intracranial hypotension. Most CSF leaks are located at the cervicothoracic junction or in the thoracic spine. The disease is often self-limiting. A CSF leak can be detected directly by accumulation of radioactivity outside the subarachnoid space or suggested indirectly by the rapid disappearance of tracer from the subarachnoid space and early appearance in the urinary bladder. In this paper we present two unusual cases of CSF leak identified by radiopharmaceutical cisternogram.

Skeletal scintigraphy with technetium-99m-tetraphenyl porphyrin sulfonate for the detection and determination of osteomyelitis in an animal model.

UNLABELLED: This article explores the accumulation of 99mTc-tetraphenyl porphyrin sulfonate (TPPS4) at inflammatory sites, especially osteomyelitis, and compares the results with 111In Cl3 and 111In-WBC in an animal model. METHODS: Osteomyelitis was induced in 12 New Zealand white rabbits by injecting staphylococcus aureus in the left tibia. Three weeks later, radiographs confirmed the disease. Two hours later, after injection of 74 MBq 99mTc-TPPS4, scintiphotos of the lower extremities were acquired and repeat scintiphotos were obtained 24 hr after injection of 5.55 MBq 111In Cl3. After these studies, 24- and 48-hr scintiphotos of the lower extremities were acquired after injecting 5.55 MBq 111In-labeled WBC. RESULTS: The left tibia averaged three times the uptake with 99mTc-TPPS4 compared with right tibia; with 111In Cl3 and 111In WBC the ratios are two times. These three radiopharmaceuticals reveal positive images, but the image quality using 99mTc-TPPS4 is better, as would be expected from the more favorable physical characteristics of 99mTc and the higher uptake. CONCLUSION: The traditional combination of three-phase bone and 67Ga-citrate scintigraphy can be replaced by a single injection of 99mTc-TPPS4 with imaging as early as 2 hr. Finally, the use 99mTc-TPPS4 should result in a substantial reduction in radiopharmaceutical cost.

Determining blood and plasma volumes using bioelectrical response spectroscopy.

We hypothesized that an electric field (inductance) produced by charged blood components passing through the many branches of arteries and veins could assess total blood volume (TBV) or plasma volume (PV). Individual (N = 29) electrical circuits (inductors, two resistors, and a capacitor) were determined from bioelectrical response spectroscopy (BERS) using a Hewlett Packard 4284A Precision LCR Meter. Inductance, capacitance, and resistance from the circuits of 19 subjects modeled TBV (sum of PV and computed red cell volume) and PV (based on 125I-albumin). Each model (N = 10, cross validation group) had good validity based on 1) mean differences (-2.3 to 1.5%) between the methods that were not significant and less than the propagated errors (+/- 5.2% for TBV and PV), 2) high correlations (r > 0.92) with low SEE (< 7.7%) between dilution and BERS assessments, and 3) Bland-Altman pairwise comparisons that indicated "clinical equivalency" between the methods. Given the limitation of this study (10 validity subjects), we concluded that BERS models accurately assessed TBV and PV. Further evaluations of the models' validities are needed before they are used in clinical or research settings.

Mediastinal scintigraphy for parathyroid localization in hyperparathyroidism.

Two cases are reported demonstrating that mediastinal scintigraphy for hyperparathyroidism should be routinely performed along with scintigraphy of the neck region. Because of the relative cost-benefit ratio, consideration should also be given to performing the procedure before the initial surgery. For the most accurate diagnosis and favorable outcome, our cases suggest that scintigraphic physiologic results should be correlated with anatomic results of conventional radiography.

The lag phase of gastric emptying: clinical, mathematical and in vitro studies.

UNLABELLED: The lag phase of gastric emptying reflects, in large measure, the clinically important milling function of the stomach, but there is little agreement on the best way to acquire, analyze and characterize lag phase data of gastric emptying studies. METHODS: Twenty normal volunteers were fed a standard 99mTc-sulfur colloid scrambled egg and toast breakfast and imaging data were acquired at 15-min intervals in both anterior and posterior projections with the subject seated. RESULTS: In a significant percentage of the subjects, the stomach count rate rose above the initial count rate, even with geometric mean correction. We attributed the count rate rise to meal self-absorption and conducted mathematical and in vitro experiments, the results of which supported this thesis. Attempts at modeling the data with power exponential fits were unsuccessful in many cases and were complex, nonintuitive and of limited clinical utility. Accordingly, gastric emptying rates were determined by simple linear regression from geometric mean data. The starting index (the time at which the regression line equalled 100%) was calculated to reflect the lag phase. Normal ranges were determined for men and women. CONCLUSION: Our method of test performance is simple, eliminates confounding variables and provides results with intuitive meaning and with direct clinical relevance.

Is silent ischemia on the routine admission ECG an important finding?

The authors' objective was to determine if, in the absence of known coronary artery disease, ST-T changes suggestive of silent ischemia on the admission electrocardiogram (ECG) identify a group of patients at high risk for cardiac event or death. A prospective cohort study was undertaken at the university hospital of a tertiary care center. All patients admitted to the hospital during the 5-month study period were screened. The authors found 54 patients with risk factors but no symptoms of coronary artery disease whose admission ECGs showed silent ischemia (ischemia group), and 71 patients with similar risk of coronary artery disease but without admission ECGs showing silent ischemia (control group). Three-week and 6-month incidences of angina, myocardial infarction, and death among patients in the silent ischemia and control groups were compared. Seven (13%) patients in the silent ischemia group had cardiac events or noncardiac death in the subsequent 3 weeks versus one (1%) noncardiac death in the control group (p < 0.02). At 6 months, eight (15%) patients in the silent ischemia group versus two (3%) in the control group had cardiac events (p = 0.02). It is concluded that among patients with risk factors but no symptoms of coronary artery disease, silent ischemia on the admission ECG is associated with an increased likelihood of short-term death or cardiac event.

Detection of subarachnoid pleural fistula.

A case of subarachnoid-pleural fistula detected by radionuclide myelography is reported. Review of the literature shows that radionuclide myelography is proving to be more sensitive than contrast myelography in confirming the diagnosis.

Population exposure from nuclear medicine procedures: measurement data.

In order to estimate the public radiation burden from nuclear medicine studies, a TLD chip in a sealed plastic bag was taped on the abdomen of patients who received 111In as chloride or oxine, 201T1 chloride, or one of four common 99mTc agents. The TLD chip was removed after 24 h. Additionally, abdominal skin surface exposure rate measurements were performed with an ionization chamber survey meter at various times (0 to about 60 h). There was superb correlation between TLD and integrated exposure rate measurements and between TLD and ionization chamber measurements and MIRD calculated doses. Scenarios postulated for exposure of co-workers and family members yielded doses between 7 muSv (0.7 mrem) and 20 muSv (2 mrem) for the selected radiopharmaceuticals. Calculations of the total population exposure from nuclear medicine procedures indicate the per capita dose (amortized over the entire population) is approximately 0.4 muSv (0.04 mrem), a negligible dose compared to natural background and total medical irradiation.

Uptake of 131I-metaiodobenzylguanidine by 6-23 rat medullary thyroid carcinoma.

Uptake of 131iodine-metaiodobenzylguanidine (131I-MIBG) by 6-23 rat medullary thyroid carcinoma (MTC), was studied in vitro and in vivo. In vitro, there was an 8-fold increase in 131I uptake by 6-23 cells when labeled with 131I-MIBG (131I 24 +/- 15 cpm/10(6) cells, 131I-MIBG 196 +/- 9 cpm/10(6) cells). MIBG uptake in vitro was the same at 4 degrees C and 37 degrees C. In contrast, 131I-MIBG uptake by PC-12 rat pheochromocytoma cells were 200 times greater (131I-MIBG 42,412 +/- 6,755 cpm/10(6) cells). 131I-MIBG uptake by rat MTC cells in vitro were of a comparable magnitude to the uptake of 131I-MIBG by rat ileal enterochromaffin cells (RIE-1) and mouse colon cancer cells (MC-26). In vivo, uptake of 131I-MIBG by 6-23 MTC tumor was considerably less than in the normal tissues (muscle, liver, spleen, kidney, adrenal and thyroid). Gamma camera studies of 131I-MIBG uptake by 6-23 MTC tumors growing in Wag-Rij rats were only transiently positive in 1 out of 4 rats studied. We conclude that 131I-MIBG is poorly taken up by rat medullary thyroid carcinoma and is an unpredictable marker for localization of rat MTC.

Correlation of right and left ventricular ejection fraction and volume measurements.

First-pass radiocardiography and biplane angiocardiography were performed on 13 patients with left-sided regurgitant valvular disease (R+) and 7 patients without regurgitation but with coronary artery disease and/or cardiomyopathy (R-). Right and left ventricular volumes and ejection fractions were calculated and compared. In the R- group, corresponding right and left ventricular volumes and ejection fractions correlated highly with each other (r = 0.86-0.89, p approximately equal to 0.01). Ejection fractions in the R+ group correlated (r = 0.64, p less than 0.05) only because stroke volume correlation was very high (r = 0.93), with end-diastolic and end-systolic volumes showing no significant correlation. Right ventricular ejection fraction (RVEF) decreased significantly with increasing mean pulmonary artery pressure (PAP) in both R- and R+ groups. The correlation of RVEF and LVEF in the R- group appears to be multifactorial in origin, consisting of effects of increased PAP, the mechanical interference of an enlarged left ventricle on the right ventricle, and direct biventricular ischemic effects. In the R+ group, the correlation appears to be due to only increased PAP and its sequelae.

First-pass anger camera radiocardiography: biventricular ejection fraction, flow, and volume measurements.

First-pass (FP) right and left ventricular ejection fraction results were compared with equilibrium radiocardiographic (ER) measurements, and FP left ventricular ejection fraction (LVEF) values were compared with biplane contrast angiographic (CA) measurements in 13 patients with and seven patients without regurgitant valvular disease. Regurgitant fractions were calculated from differences between the FP right and left ventricular stroke volumes. Ejection fractions determined by FP were precise (mean CV = 9.6% RVEF, 13.4% LVEF). Mean LVEF by FP and ER were essentially identical, and both were lower than by CA. LVEF(FP) correlated with LVEF by ER and CA (r = 0.88, p less than 0.001). Mean RVEF by both FP and ER were also correlated (r = 0.82, p less than 0.001). There was correlation between FP (corrected) and CA left ventricular stroke (r = 0.77), end-diastolic (r = 0.88), and end-systolic (r = 0.91) volumes, but underestimates were noted when uncorrected flows were used (r = 0.52-0.71). The FP regurgitant fraction measurements separated the patients with regurgitant valvular disease from those without and agreed well with CA grading of regurgitation.

Is there a thyrotoxic cardiomyopathy in children?

We measured left ventricular ejection fraction by radionuclide angiocardiography at rest and during graded exercise in eight thyrotoxic children. Five patients were reassessed after return to a clinically euthyroid state. In the thyrotoxic state the left ventricular ejection fraction was 69% +/- 8% at rest, and increased normally by 7% to 10% during exercise in four patients but did not change significantly or decreased by as much as 8% in the other four patients. The change in left ventricular ejection fraction during exercise correlated inversely with serum concentrations of thyroxine (r = -0.82, P less than 0.02) and triiodothyronine (r = -0.88, P less than 0.01). A comparison between patients who had normal left ventricular response to exercise with those who had abnormal response while thyrotoxic failed to uncover any significant differences between their resting ejection fractions or resting and exercise heart rates and systolic blood pressures. Three abnormal and two normal responders were reassessed after return to a clinically euthyroid state. The left ventricular ejection was 64% +/- 6% at rest, and increased during exercise in all patients. Our study suggests that thyrotoxicosis causes diminished left ventricular reserve (compensated functional cardiomyopathy) in some patients, but appears to be reversible. Severity of thyrotoxicosis, as measured by thyroid hormone blood levels, may be a determining factor in the development of functional cardiomyopathy.

Verification of global cerebral ischaemia using scintigraphy.

The induction of global cerebral ischaemia in laboratory animals is difficult to accomplish and has been even more difficult to verify. Most reported verification methods suffer from lack of sensitivity or from being traumatic and highly invasive. We describe a non-traumatic global cerebral ischaemia verification technique which is quantitative, simple, and highly sensitive. Radioactive technetium-99m pertechnetate is injected intravenously during the ischaemic phase of an experiment and the appearance of radioactivity within the animal's head is quantitated using a gamma camera and nuclear medicine computer. Radioactivity levels below the visual perception threshold are readily measured, thus providing a high degree of confidence in assessing the partial or total nature of cerebral ischaemia.

Accurate estimates of absolute left ventricular volumes from equilibrium radionuclide angiographic count data using a simple geometric attenuation correction.

To simplify and clarify the methods of obtaining attenuation-corrected equilibrium radionuclide angiographic estimates of absolute left ventricular volumes, 27 patients who also had biplane contrast cineangiography were evaluated. Background-corrected left ventricular end-diastolic and end-systolic counts were obtained by semiautomated variable and hand-drawn regions of interest and were normalized to cardiac cycles processed, frame rate and blood sample counts. Blood sample counts were acquired on (d degree) and at a distance (d') from the collimator. A simple geometric attenuation correction was performed to obtain absolute left ventricular volume estimates. Using blood sample counts obtained at d degree or d', the attentuation-corrected radionuclide left ventricular end-diastolic volume estimates using both region of interest selection methods correlated with the cineangiographic end-diastolic volumes (r = 0.95 to 0.96). However, both mean radionuclide semiautomated variable left ventricular end-diastolic volumes (179 +/- 100 [+/- 1 standard deviation] and 185 +/- 102 ml, p less than 0.001) were smaller than the average cineangiographic end-diastolic volume (217 +/- 102 ml), and both mean hand-drawn left ventricular end-diastolic volumes (212 +/- 104 and 220 +/- 106 ml) did not differ from the average cineangiographic end-diastolic volume. Using the blood sample counts obtained at d degree or d', the attenuation-corrected radionuclide left ventricular end-systolic volume estimates using both region of interest selection methods correlated with the cineangiographic end-systolic volumes (r = 0.96 to 0.98). Also, using blood sample counts at d degree, the mean radionuclide semiautomated variable left ventricular end-systolic volume (116 +/- 98 ml, p less than 0.05) was less than the average cineangiographic end-systolic volume (128 +/- 98 ml), and the other radionuclide end-systolic volumes did not differ from the average cineangiographic end-systolic volume. Therefore, it is concluded that: 1) a simple geometric attenuation-correction of radionuclide left ventricular end-diastolic and end-systolic count data provides accurate estimates of biplane cineangiographic end-diastolic and end-systolic volumes; and 2) the hand-drawn region of interest selection method, unlike the semiautomated variable method that underestimates end-diastolic and end-systolic volumes, provides more accurate estimates of biplane cineangiographic left ventricular volumes irrespective of the distance blood sample counts are acquired from the collimator.