Enzyme replacement therapy for Gaucher disease: skeletal responses to macrophage-targeted glucocerebrosidase.

OBJECTIVES: Reversal of the hematologic and visceral abnormalities characteristic of Gaucher disease, the most common lipid storage disorder, with biweekly infusions of macrophage-targeted glucocerebrosidase (glucosylceramidase) is well documented. The extent to which the skeleton responds to enzyme replacement therapy has not been systematically investigated. METHODS: To assess the skeletal response to enzyme replacement therapy, we treated 12 patients with type 1 Gaucher disease, who had intact spleens, with macrophage-targeted glucocerebrosidase. The initial dose of enzyme was 60 U/kg body weight every 2 weeks for 24 months, followed by reduction in dosage to 30 and then 15 U/kg body weight every 2 weeks, each for 9 months. RESULTS: The lipid composition of bone marrow, determined by direct chemical analysis, began to improve after 6 months of treatment at a time when noninvasive imaging studies showed no significant changes. By 42 months, improvement in marrow composition was demonstrable on all noninvasive, quantitative imaging modalities (magnetic resonance score, quantitative xenon scintigraphy, and quantitative chemical shift imaging) used in this study. Quantitative chemical shift imaging, the most sensitive technique, demonstrated a dramatic normalization of the marrow fat content in all patients. Net increases in either cortical or trabecular bone mass, as assessed by combined cortical thickness measurements and dual-energy quantitative computed tomography, respectively, occurred in 10 patients. CONCLUSIONS: Prolonged treatment over 3 1/2 years with macrophage-targeted glucocerebrosidase produces objective reversal of disease in both the axial and appendicular skeleton in patients with Gaucher disease. Marked improvement occurs in marrow composition and bone mass in both children and adults.

Expiratory flow pattern following single-lung transplantation in emphysema.

In single lung transplantation (SLT) recipients, a "plateau" of the maximal expiratory flow volume curve (MEFV) and a "biphasic" MEFV have been reported to reflect anastomosis pathology. A plateau is defined as constant airflow over a large expired volume early in the MEFV. A biphasic MEFV has an initial period of high flow followed by a terminal low flow phase. Models of expiratory flow limitation by wave speed, however, predict that the MEFV of SLT recipients with emphysema should both be biphasic and demonstrate a plateau even without anastomosis pathology. Review of the spirometries and clinical courses of our first ten patients receiving SLT for emphysema demonstrated a biphasic MEFV, and a plateau of the MEFV in all patients. No patient showed evidence of anastomosis pathology. Independent lung spirometries, generated by a novel technique, revealed that the initial high flow phase of the MEFV came from the transplanted lung and the terminal low flow from the native emphysematous lung. The location of the flow limitation was demonstrated to be immediately downstream from the anastomosis. Therefore, the MEFV of SLT recipients with emphysema routinely demonstrates both a biphasic pattern and a plateau, neither of which necessarily reflect anastomosis pathology.

Dosimetric consequences of radiopharmaceutical infiltrations.

RATIONALE AND OBJECTIVES: Little is known about the time-related biologic behavior of radiopharmaceutical misinjections. Such inadvertent tissue infiltration of such injections may not only adversely affect a scheduled test or cause some discomfort, but potentially could produce tissue damage. Radiopharmaceutical infiltrations were assessed in a rat model. METHODS: Particulate and nonparticulate radiopharmaceuticals were injected subcutaneously or intradermally into an anesthetized shaved rat model. The rate of release of the nine infiltrations per radiopharmaceutical per injection type were measured from computer data acquired with a gamma camera up to 24 hours after administration. These data were used for dosimetry determinations. RESULTS: When injected subcutaneously, the particulate radiopharmaceutical, technetium 99m (99mTc) albumin microspheres, exhibited essentially no movement, and the soluble agents showed a biexponential release pattern. The rate of release was similar for 99mTc methylene diphosphonate (99mTc MDP) and for 67Ga citrate (67Ga), whereas thallous chloride (201Tl) exhibited the slowest release pattern. The average effective half-lives (T1/2 av-eff) were 78.3 minutes, 76.1 minutes, and 268.4 minutes, respectively. When injected intradermally, the nonparticulates exhibited a triexponential release pattern; MDP showed a more rapid release (T1/2 av-eff, 50 minutes) and 201Tl showed the slowest (T1/2 av-eff, 491.2 minutes). Absorbed doses were calculated using conventional medical internal radiation dose (MIRD) methodology for small unit density spheres. The absorbed dose was greatest for a 201Tl infiltration. A 201Tl infiltrate of 1 mCi per gm of tissue is capable of producing radiation-absorbed doses greater than 500 rads. Additional studies were performed with heat, hyaluronidase, and volume dilution in an attempt to accelerate the rate of release of 201Tl. Local heat application proved to be more efficient than volume change or hyaluronidase application. CONCLUSION: These data indicate an insignificant skin radiation burden from the majority of nonparticulate infiltrated radiodiagnostic agents. Thallium 201, however, has the potential to produce significant radiation burdens when infiltrated at high specific activity. Actual human infiltration release rates may differ because of variants in blood flow and assumed infiltration volume relative to the animal model.

Radiopharmacology of inhaled 133Xe in skeletal sites containing deposits of Gaucher cells.

Gaucher's disease is a lysosomal storage disease in which cells of the reticuloendothelial system accumulate the lipid glucocerebroside. It is characterized by slowly progressive visceral and osseous involvement. One of the latter manifestations includes lipid infiltration of bone marrow. We monitored the rate of inhaled 133Xe uptake and wash-out over diseased and normal metaphyseal and epiphyseal areas of the knee. Twenty-two patients (15 adults, 7 children) with various degrees of previously diagnosed Gaucher's disease were positioned supine under a gamma-camera interfaced to a computer system. All patients rebreathed 133Xe gas from a closed system for 10 min followed by 14 min of wash-out. Digitized images of the lung, liver, spleen, bony sites and soft tissue were obtained at 1 min intervals during the wash-in and wash-out phases. Counts for each ROI were normalized per 100 pixels and plotted as a function (time). Maximum uptake was also calculated by relating the counts/ROI/100 pixels to the 10 min integrated lung count during equilibrium (the administered "dose"). There was essentially no 133Xe uptake in liver and spleen involved with Gaucher's disease. Monophasic uptake and biphasic wash-out curves were observed in the limited investigative population. Skeletal Gaucher deposits released the 133Xe at a greater rate relative to soft tissue.

Ventilation-perfusion scintigraphy in the PIOPED study. Part I. Data collection and tabulation.

The Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study of more than 700 patients is the largest existing study of the accuracy of lung scintigraphy in the diagnosis of acute pulmonary embolism. Perfusion scans were obtained in all patients and ventilation scans in almost all, using standardized techniques. Chest radiographs were obtained in all patients within 12 hr of the lung scan. Most patients underwent pulmonary arteriography. The images were interpreted according to a set of interpretive criteria which remained constant throughout the trial. A standardized, detailed description of each image set was derived by consensus of teams of two readers blinded to clinical and arteriographic findings. This communication reports the methods used to describe and categorize the ventilation-perfusion scintigrams obtained in patients who were enrolled in the PIOPED study. Scintigraphic technique is reviewed briefly, probability assessment is described and the scan description is reviewed in detail. The form used to describe the findings on ventilation-perfusion scans is reproduced. Use of this standardized description permits retrospective evaluation of the PIOPED interpretive criteria. In addition, it represents a rigorous approach to scan analysis which could facilitate application of formal interpretive schemes and enhance the reproducibility of lung scan interpretations in the clinical setting.

Ventilation-perfusion scintigraphy in the PIOPED study. Part II. Evaluation of the scintigraphic criteria and interpretations.

This article presents an evaluation of the criteria used for categorical interpretation of the ventilation-perfusion (V/Q) scans performed in the PIOPED study. In addition, the correlation of percent probability estimates with the actual frequency of pulmonary embolism (PE) is presented. Cases which met the PIOPED criteria for various diagnostic categories were selected by computerized search of the detailed scan descriptions that had been done as part of the study. The process by which the scans were described was detailed in Part I of this report. Most of the criteria appropriately categorized V/Q scans which satisfied them. However, we recommend that three criteria should be reconsidered: 1. A single moderate perfusion defect is appropriately categorized as intermediate, rather than as low probability. 2. Extensive matched V/Q abnormalities are appropriate for low probability, provided that the chest radiograph is clear. On the other hand, single-matched defects may be better categorized as intermediate probability. Although due to the small number of cases with this finding, no definite, statistically founded recommendation can be made. 3. Two segmental mismatches may not be the optimum threshold for high probability, and in some cases should be considered for intermediate probability. However, due to the small number of cases with this finding, no definite, statistically founded recommendation can be made. We suggest that the revised criteria resulting from these adjustments should now be used for the interpretation of V/Q scans.

Characterization of the reinjection thallium image.

The 201TI image after reinjection was characterized by analysis of stress and reinjection data acquired in 204 consecutive patients undergoing planar 201TI cardiac stress tests. In an additional 63 patients, redistribution data were also acquired to determine the effect of washout on the final reinjection image. Maximum count densities for the myocardium, lung and liver were measured, and the ratios between the stress and redistribution and the stress and reinjection sets of data were calculated. In patients with < 5% probability of coronary artery disease (CAD) ("normal" group), the reinjection image was typified by less myocardial activity (initial/reinjection = 1.22), slightly less lung activity (initial/reinjection = 1.05) and greater hepatic activity compared to the initial postexercise image. In male patients with > 5% probability of CAD, peak myocardial activity after reinjection was affected by the following variables: the interval between stress and reinjection, the amount of the initial dose and the 201TI scan results (normal 201TI study: initial/reinjection = 1.16; abnormal = 1.06; p < 0.009). Myocardial activity after reinjection was linearly related to myocardial activity after redistribution (r = 0.82). There was no significant influence by those variables in the 76 women who were studied. In conclusion, myocardial 201TI was decreased after reinjection in normal patients. The results indicate that there is an increased likelihood of underlying CAD in male patients undergoing exercise stress tests when 201TI myocardial activity on reinjection is greater than on the initial image.

Current procedural terminology coding of nuclear medicine procedures.

The future of nuclear medicine is dependent on payment for new procedures. Today, the basis of payment by the federal government is a relative value unit (RVU) system; the RVUS employed in this system are for medical services and procedures listed and described in Physicians' Current Procedural Terminology, fourth edition. Current procedural terminology (CPT) is maintained by the AMA; annual revisions include adding new codes or revised or deleted old codes. This process involves all national medical specialty societies. Starting in 1992 a new process, the Relative Updating Committee, which was initiated by the AMA, organized medicine to formalize a method for recommending relative values for physician procedures and services. In this rapidly changing scenario, all nuclear medicine procedure codes are under review by the coding and nomenclature committees of the medical societies interested in imaging. Significant CPT changes and additions were made in the cardiovascular nuclear medicine codes in 1992, reflecting the current imaging protocols and pharmacological agents for performing cardiac stress testing and new codes that recognize combinations of ventricular function measurements in patients undergoing myocardial perfusion imaging with technetium-99m agents.

Quantitative imaging of Gaucher disease.

Twenty-three patients with type 1 Gaucher disease were evaluated with a battery of quantitative imaging techniques. Plain radiographs were used to measure cortical thickness and Erlenmeyer flask deformity. Xenon-133 uptake was measured in scans of the lower extremities. Dual-energy quantitative computed tomography was used for calculation of trabecular bone and bone marrow fat content in the spine and long bones. Magnetic resonance (MR) imaging was performed to evaluate disease extent and three-dimensional splenic volume. MR images were also used to provide quantitative measurements of each vertebral fat fraction. Each imaging modality was correlated with the others as well as with the clinical history of skeletal complications and the hematocrit and acid phosphatase activity. There was a strong relationship between splenic volume and disease severity as measured clinically and with laboratory testing. The spinal fat fraction also correlated with these measures of disease severity and with the femoral fat fraction and xenon uptake. No measurement allowed discrimination of patients with from those without skeletal complications.

A prospective investigation of pulmonary embolism in women and men.

OBJECTIVE: The aim of this study was to compare, in women and men suspected of pulmonary embolism, the frequency, risk factors, diagnosis, and presentation of pulmonary embolism as well as the accuracy of the ventilation/perfusion scan (V/Q scan) as a diagnostic tool. DESIGN: Data were collected during a prospective study (the Prospective Investigation of Pulmonary Embolism Diagnosis) to establish the accuracy of the V/Q scan compared with pulmonary angiograms. SETTING: Six tertiary medical centers in Massachusetts, Michigan, Connecticut, Pennsylvania, and North Carolina. PARTICIPANTS: Patients suspected of pulmonary embolism for whom a request was made for a V/Q scan or pulmonary angiogram (496 women and 406 men). RESULTS: Women 50 years old and under had a decreased frequency of pulmonary embolism compared with men of that age (16% vs 32%), but there was no difference in patients over 50 years old (Breslow-Day test, P less than .01). Risk factors for pulmonary embolism, the usefulness of the V/Q scan, and 1-year mortality were not different for women and men. Estrogen use in women was not associated with an increased frequency of pulmonary embolism, except in women using oral contraceptives who had undergone surgery within 3 months; four of five (80%) had emboli compared with four of 28 (14%) age-matched surgical patients not using estrogens (P less than .01). CONCLUSION: Women 50 years old and under (even young women using oral contraceptives) who were suspected of having pulmonary emboli and were enrolled in the Prospective Investigation of Pulmonary Embolism Diagnosis study had a smaller frequency of pulmonary embolism than men of that age, The risk factors for pulmonary embolism were the same for women and men, except that women using oral contraceptives had an increased risk of pulmonary embolism following surgery. Although the V/Q scan was a useful tool in the preliminary evaluation for pulmonary embolism in these women, a pulmonary angiogram was often needed for accurate diagnosis.

Blood flow of human soft tissue sarcomas measured by thallium-201 scanning: prediction of tumor response to radiation.

Thallium-201 chloride (201T1) has been used to determine regional perfusion in the myocardium and in tumors. This study was done to determine the potential prognostic importance of lesion tracer uptake to regression, local control, and rate of distant metastasis in 14 patients with neoplasms of soft tissue. Most patients had planned resections following preoperative radiation therapy. Minimum follow-up was 4 years. The ratio of nuclide uptake in the tumor to surrounding normal tissue was used as an estimate of relative blood flow. Tumors with acute volume responses (greater than or equal to 50% at the completion of X irradiation) had lower 201T1 uptake indicating lower relative blood flow than tumors that failed to have a volume reduction [1.63 +/- 0.30 (n = 9) vs 3.49 +/- 0.41 (n = 5) 201T1]. All patients had local tumor control. Patients with high uptake tumors tended to develop metastases at a higher frequency, although this was not statistically significant (p = 0.10). We conclude that 201T1 scans are a safe, non-invasive method of estimating tumor perfusion which can be useful to predict acute response to radiation, and may help to identify patients who will ultimately develop distant metastases.

Comparison of thallium redistribution with rest "reinjection" imaging for the detection of viable myocardium.

To determine the incidence of incomplete redistribution on conventional delayed thallium images, 41 patients with persistent perfusion defects on myocardial images recorded 3 to 4 hours after thallium injection during exercise were studied. At the conclusion of their delayed images the patients were reinjected at rest with approximately 1 mCi of thallium-201 and a third set of images was recorded. The images were presented at random in pairs (initial:delayed, initial:reinjection) to 2 experienced observers for qualitative scoring of 9 segments/patient. Of the 360 segments analyzed, concordance between the delayed and reinjected images occurred in 307 (85%). Of 141 segments that demonstrated a persistent perfusion abnormality on 3- to 4-hour delayed images, 44 (31%) were reassigned to a redistribution score after reinjection. In 9 patients, reinjection images provided the only evidence of ischemia from the scintigraphic data. In 13 of 14 vascular territories that demonstrated redistribution after reinjection, intact perfusion (either anterograde or via collaterals) was detected at coronary angiography. These data suggest that rest reinjection imaging may provide a means of detecting viable myocardium in segments that demonstrate a fixed perfusion abnormality on conventional 3- to 4-hour delayed thallium images.

Serial evaluation of right ventricular dysfunction associated with acute inferior myocardial infarction.

Right ventricular (RV) function was evaluated serially by multigated blood pool imaging in 18 patients with RV dysfunction associated with acute inferior myocardial infarction. Radionuclide ventriculograms were performed on all patients within 18 hours of chest pain and again at 10 days. In addition, 15 of 18 patients had rest and exercise radionuclide ventriculograms at 3 months. The mean resting right ventricular ejection fractions (RVEF) at admission, 10 days, and 3 months in these patients was 31.8 +/- 12.6% (SD), 46.9 +/- 11.2% (p less than 0.05), and 44.5 +/- 10.2% (p less than 0.05), while the left ventricular ejection fractions were 55.9 +/- 10.6%, 57.9 +/- 13.3%, and 53.1 +/- 11.2% (p = ns). The 3-month exercise radionuclide ventriculogram demonstrated an increase in RVEF greater than 5% in 6 of 15 patients. In eight catheterized patients, neither the location nor the severity of coronary artery narrowing nor the presence of collaterals correlated with the RV exercise response. Improvement in RV function over a 10-day interval following acute inferior myocardial infarction suggests the presence of significant reversible right ventricular dysfunction during the acute phase.

Myocardial perfusion imaging with a new radiotracer, technetium-99m-hexamibi (methoxy isobutyl isonitrile): comparison with thallium-201 imaging.

Technetium-99m-hexamibi (methoxy isobutyl isonitrile) is a Tc-99m-hexakis analog that can be used as a myocardial perfusion imaging agent. This is a report of an initial study that was performed in four institutions to assess the feasibility of Tc-99m-hexamibi myocardial imaging for the detection of coronary artery disease in patients undergoing treadmill stress test. Thirty-three patients referred for evaluation of chest pain had two exercise stress tests, one with Tl-201 and at least 24 hours after, and a second one with Tc-99m-hexamibi. Myocardial planar imaging started 60 minutes after injection at stress of 10-20 mCi of Tc-99m-hexamibi. Because this agent does not redistribute in myocardium after a stress injection, a second injection of 10-20 mCi of Tc-99m-hexamibi was performed with the patient at rest a few days later. Qualitative assessment of both Tl-201 and Tc-99m-hexamibi myocardial distribution was performed in 297 left ventricle segments (three segments of each of three views). There was a good correlation for the presence of normality, scar, or ischemia with the two radiopharmaceuticals, both on a segment by segment (259/297, or 87.2%) and patient-by-patient basis (29/33, or 87.9%). The number of segments found ischemic with Tl-201 and with Tc-99m-hexamibi were nearly equal, as were the number that were normal with one radiopharmaceutical and ischemic by the other. This initial study demonstrates that it is possible to detect stress-induced abnormalities of myocardial perfusion with Tc-99m-hexamibi similar to Tl-201 imaging.

Left ventricular performance during psychological stress.

Left ventricular ejection fraction, systolic blood pressure and plasma norepinephrine were measured in six normotensive and six mildly hypertensive subjects during rest and psychological stress. Compared with rest, 8 of the 12 subjects developed significant (P less than 0.05) changes in ejection fraction (increase in 6, decrease in 2); 10 of 12 subjects developed significant elevations of plasma norepinephrine; and all developed significant increases in systolic blood pressure. When the stress effects were examined for the total group, as opposed to within subjects, there were significant increases in plasma norepinephrine (P less than 0.001) and systolic blood pressure (P less than 0.001) but, interestingly, mean ejection fraction and stroke volume remained unchanged, implying stress led to increased left ventricular contractility.

Redistribution of visceral blood volume in upright exercise in healthy volunteers.

Exercise induced changes in the blood volume of visceral organs (cardiopulmonary and liver, spleen, and kidneys) were determined by scintillation camera imaging of the distribution of technetium-99m-labeled red blood cells in the thorax and abdomen of ten healthy adult volunteers. Graded upright bicycle exercise was performed to the point of exhaustion with the volunteer positioned with his/her back to the scintillation camera and data recording was synchronized to the pedal cycle to minimize patient motion artifacts within the data. The first image from each level of exercise was analyzed by placing regions of interest over the spleen, liver, kidneys, and right lung. The counts in each organ were expressed as a percent of activity at zero workload. Analysis of data using Hotelling's t-squared analysis to see if overall differences existed between the last four measurements (up to the time of exhaustion) regarding percent change from baseline for spleen, kidney, liver, and right lung were made. The splanchnic bed had a significant decrease in blood volume. The spleen decreased 39%, while the liver decreased 14%. For the kidney and liver, no significant differences were achieved (p greater than 0.24, p less than 0.15, respectively). The lung increased its blood volume to 128% of control, significant with p less than 0.02. This data demonstrates that in healthy volunteers there is normal redistribution of blood volume during maximal exercise with a significant reduction in blood volume of the spleen as well as a significant rise in blood volume within the lungs.

Imaging human atherosclerosis with 99mTc-labeled low density lipoproteins.

The feasibility of localizing human atherosclerotic plaques by gamma scintillation camera external imaging with technetium-99m-labeled low density lipoproteins (99mTc-LDL) was tested in 17 patients who had atherosclerosis. Imaging demonstrated focal accumulation of radiolabel consistent with 99mTc-LDL sequestration by plaques in the carotid, iliac, or femoral vessels of four patients 8 to 21 hours after intravenous injection of the radiopharmaceutical. Focal accumulation of 99mTc-LDL also appeared in the location of coronary lesions in four patients, but this accumulation could not be distinguished with certainty from residual blood pool radioactivity. When carotid endarterectomy specimens from six patients who received 99mTc-LDL 1 day before endarterectomy were examined, the specimens had focal accumulations of radiolabel, with two to four times greater radioactivity in some regions of each specimen than in others; this occurred whether or not the lesions were detected on the gamma camera images. Lesion composition may have determined whether accumulation was quantitatively sufficient to produce an external image. Histologically, the imaged carotid specimen had abundant foam cells and macrophages and poorly organized intramural blood consistent with a plaque hemorrhage; in contrast, nonimaged endarterectomy specimens were mature, fibrocalcific plaques. We conclude that: 1) 99mTc-LDL did accumulate in human atherosclerotic plaques; 2) in some patients, the accumulation of 99mTc-LDL was sufficient for detection by gamma camera imaging; 3) the amount of LDL that accumulated appeared to depend on lesion composition; and 4) the design of new radiopharmaceuticals with reduced residual blood pool activity relative to plaque accumulation should lead to improved external imaging of atherosclerosis.