Three-phase bone scintigraphy of hydroxyapatite ocular implants

Hydroxyapatite ocular implants are replicas of lamellar bone tissue derived from the exoskeleton of a reef-building coral by a hydrothermal chemical exchange reaction. Attached to the eye muscles, they act as a passive framework for fibrovascular ingrowth and can be drilled to hold the visible part of the artificial eye and allow synchronous eye movement. Fibrovascular ingrowth has to be confirmed by bone scintigraphy before the drilling procedure. This study monitored the vascular ingrowth into the implant in ten patients over 12 months to establish a clinically feasible imaging protocol. Tracer accumulation was monitored visually and quantitatively in dynamic and single-photon emission tomography (SPET) scans after the intravenous administration of 600 MBq of^99mTc-DPD. The implants showed no tracer accumulation in the arterial or blood pool phase. Accordingly, dynamic scintigraphy can be omitted from the imaging protocol. Delayed tracer accumulation appeared no earlier than 2 and no later than 6 months after surgery. Planar scintigraphy is not recommended as high-resolution SPET is necessary to separate the implant from the surrounding bone. We conclude that imaging can be confined to high-resolution SPET 3 h after tracer injection, no earlier than 3 months after surgery. The vascularized hydroxyapatite orbital implant is an important in vivo model for bone-seeking agents to study their uptake kinetics independently of any soft tissue and bone disease. Our results provide evidence that in normal bones the chemical adsorption of^99mTc-DPD into the crystalline structure of hydroxyapatite is the only quantitatively relevant uptake mechanism.     

Evaluation of vascularization of coralline hydroxyapatite ocular implants by magnetic resonance imaging

A coralline hydroxyapatite orbital implant may be placed after ocular enucleation or evisceration. It must be vascularized to support epithelialization of a hole drilled in its anterior face for insertion of a motility peg. We used gadolinium-DTPA enhanced magnetic resonance imaging (MRI) of the orbits of two patients to assess fibrovascular penetration into their implants. MRI provides a reliable determination of implant vascularization and greater anatomic detail than 99m technetium-MDP bone scanning.     

Assessment of skull base involvement in nasopharyngeal carcinoma: comparisons of single-photon emission tomography with planar bone scintigraphy and X-ray computed tomography

The diagnostic contribution of single-photon emission tomography (SPET) to the detection of bone lesions of the skull base was explored in 200 patients with nasopharyngeal carcinoma (NPC). Comparison of SPET with planar bone scintigraphy showed that SPET improved the contrast and better defined the lesions in 107 out of the 200 patients. Comparison of SPET with X-ray computed tomography (CT) showed that SPET did not miss the lesions detected by CT while CT missed 49% of the lesions detected by SPET. The only false-positive lesion with SPET was detected in the mastoid bone. SPET detected skull base lesions in all of the 35 patients with cranial nerve involvement, while CT missed eight and planar bone scintigraphy missed four. The findings suggest that SPET should be included in the routine check-up examinations of patients with NPC.     

Alternative positron emission tomography with non-conventional positron emitters: effects of their physical properties on image quality and potential clinical applications

The increasing amount of clinically relevant information obtained by positron emission tomography (PET), primarily with fluorine-18 labelled 2-deoxy-2-fluoro-d-glucose, has generated a demand for new routes for the widespread and cost-efficient use of positron-emitting radiopharmaceuticals. New dual-head single-photon emission tomography (SPET) cameras are being developed which offer coincidence detection with camera heads lacking a collimator or SPET imaging with specially designed collimators and additional photon shielding. Thus, not only satellite PET imaging units but also nuclear medicine units investing in these new SPET/PET systems need to examine all available alternatives for rational radionuclide supplies from host cyclotrons. This article examines 25 ”alternative” positron-emitting radionuclides, discusses the impact of their decay properties on image quality and reviews methods for their production as well as for their application in imaging techniques.     

Validation of automated brain contour determination in normal and abnormal cerebral single-photon emission tomography

A contour detection algorithm for cerebral studies, using the method of Tomitani, has been implemented on a single-photon emission tomographic (SPET) system. It is based on the detetion by threshold of the brain edge in the sinogram and does not depend on the reconstruction algorithm. Thirteen normal subjects underwent an examination on both computed tomography (CT) and SPET using a head holder to ensure the reproducibility of the positioning. The CT scan contour of the brain was drawn manually according to the brain parenchyma limits. The SPET brain contour was obtained by use of the Tomitani algorithm after the threshold had been determined on an active cylindrical phantom. Using a threshold of 37% of the maximum uptake, the length of the contour as well as the area obtained with SPET and CT were not found to be statistically different. The method of Tomitani, which is simpler and faster then previous methods, provides contours which superimpose very well with CT scan images. Application to patients with unilateral pathological defects is possible by requiring that the contour is symmetrical.     

Performance comparison of a state-of-the-art neuro-SPET scanner and a dedicated neuro-PET scanner

The physical performances of two current state-of-the-art scanners dedicated to functional imaging of the brain, one a single-photon emission tomography (SPET) scanner and the other a positron emission tomography (PET) scanner, have been compared under identical conditions. The aim of the study was to compare the capabilities of the devices under conditions resembling the routine clinical environment, as well as to consider other issues such as radiation burden for some common investigations. Both systems have slightly less than 11-cm axial fields of view. The PET system can be operated in a septa-less (3D) mode as well as conventionally with septa (2D). The spatial resolution of both devices was less than 8 mm in all dimensions in scattering media. On average, the PET scanner's resolution was approximately 10%–15% better than the SPET system. Energy resolution on the SPET system was superior due the scintillator used [Nal(Tl)]. Sensitivity in air with a line source on the PET system was found to be 150 times greater in 3D and 25 times greater in 2D than with the SPET system. A normal subject was studied on each system in an attempt to obtain the highest quality data possible for a subjective comparison. It is clear that, while PET retains the advantages of more desirable radiopharmaceuticals and higher sensitivity, the quality obtainable from SPET devices has improved markedly. SPET may prove as useful for many clinical investigations.     

External reference markers for the correction of head rotation in brain single-photon emission tomography

Accurate reorientation of brain single-photon emission tomography (SPET) is required for quantitative procedures and for correlation with other imaging modalities. Traditionally, brain SPET has utilized reoriented slices parallel to the orbitomeatal line (OML). Reorientation using internal landmarks would be more convenient but has not been systematically compared with the use of external landmarks. We compared the interobserver reproducibility for defining the sagittal and coronal angular deviations using internal landmarks, a visual method based upon external reference markers, and an automated method based upon external reference markers. Internal landmarks were inaccurate for defining the OML whether this was based upon the frontal-occipital or frontal-cerebellar plane. External reference markers resulted in significantly lower interobserver differences for both sagittal and coronal reorientation. An operator-independent implementation proved to be feasible and provided an objective measure of marker coplanarity. In summary, external reference markers should be used when reproducible reorientation and ROI placement are required.     

Delayed cerebral radionecrosis with a high uptake of 11C-methionine on positron emission tomography and 201Tl-chloride on single-photon emission computed tomography

A 47-year-old woman, who 2.5 years previously had undergone resection of a malignant astrocytoma of the left temporal lobe followed by radiotherapy, was found to have a mass in the left frontal lobe. This showed high uptake of thallium-201 (²⁰¹Tl) on single-photon emission computed tomography and ¹¹C-methionine on positron-emission tomography, suggesting recurrent tumour. Histological examination of the resected lesion, however, revealed it to be radionecrosis. This case thus illustrates a diagnostic pitfall in the use of these investigations for distinguishing radionecrosis from recurrent malignant glioma. Received: 19 September 1997 Accepted: 16 October 1997     

Assessment of myocardial perfusion and viability with technetium-99m methoxyisobutylisonitrile and thallium-201 rest redistribution in chronic coronary artery disease

We compare thallium-201 rest redistribution and fluorine-18 fluorodeoxyglucose ([¹⁸F]FDG) for the assessment of myocardial viability within technetium-99m methoxyisobutylisonitrile (MIBI) perfusion defects in 27 patients with chronic stable coronary artery disease. The following studies were performed: (1) stress^99mTc-MIBI, (2) rest^99mTc-MIBI, (3)²⁰¹T1 rest-redistribution single-photon emission tomography, (4) [¹⁸F]FDG positron emission tomography. The left ventricle was devided into 11 segments on matched tomographic images. The segment with the highest activity at stress was taken as the reference (activity=100%). Perfusion defects at^99mTc-MIBI rest were classified as severe (activity<50%), moderate (activity 50%–60%) or mild (activity 60%–85%). Uptakes of [¹⁸F]FDG and rest-redistributed²⁰¹Tl were recognized as significant if they exceeded 50% of that in the reference segment. Among the 33 segments with severe^99mTc-MIBI rest perfusion defects, 21 had significant [¹⁸F]FDG and 10 significant rest-redistributed²⁰¹Tl uptake. As regards the 37 segments with moderate defects, [¹⁸F]FDG was present in 29 and²⁰¹Tl in 31, while of the 134 segments with mild defects, 128 showed [¹⁸F]FDG uptake, and 131,²⁰¹Tl uptake. In conclusion, there is an inverse relationship between the severity of^99mTc-MIBI perfusion defects and the uptake of rest-redistributed²⁰¹Tl and [¹⁸F]FDG. Both tracers are adequate markers of viability in mild and moderate defects; in severe defects²⁰¹Tl might underestimate the presence of viability as assessed by [¹⁸F]FDG.     

Bone single-photon emission tomography in recent meniscal tears: an assessment of diagnostic criteria

Bone single-photon emission tomography (SPET) was performed in 40 patients within 6 months of acute knee injury where internal derangement of the knee was suspected, and the results related to the arthroscopy findings. Scan features with high sensitivity, specificity, and predictive accuracy for a meniscal tear could not be obtained on planar imaging. However, a half-crescent or more of increased tibial plateau activity on transaxial SPET gave a sensitivity of 89%, a specificity of 76%, a positive predictive accuracy of 77% and a negative predictive value of 89%. For longitudinal (bucket handle) tears alone the optimum scan pattern was a full crescent of increased tibial plateau activity with adjacent femoral activity and increased blood pool activity which gave corresponding values of 78%, 94%, 78% and 93%. It is concluded that the inclusion of tibial plateau activity of less than a full crescent and the presence of femoral condyle and blood pool activity in the diagnostic criteria improves the ability of bone SPET to detect meniscal tears. The value of bone SPET in the diagnosis of meniscal tears suggests that it could have a significant role to play in the management of knee injuries. Correspondence to: P.J. Ryan     

核素显像在原发性醛固酮增多症患者中的应用

原发性醛固酮增多症（PA）是指体内无法抑制的醛固酮高分泌,导致肾素-血管紧张素系统被激活从而引起机体一系列病理生理改变的临床综合征。PA分为单侧和双侧肾上腺醛固酮分泌过多,两者的治疗方式存在本质差异,前者多采用手术治疗,而后者多采用药物治疗,如何早期分型对下一步的治疗具有重要的临床意义。核素显像包括正电子发射断层显像术（PET）与单光子发射断层显像术（SPECT）,它们以分子探针、功能显像及无创性等为特征,在PA患者的分型诊断中发挥着越来越重要的作用。笔者就核素显像在PA中的研究进展进行综述。     

Regional cerebral blood flow in Angelman syndrome

A patient with typical features of Angelman syndrome — a genetically inherited disorder involving developmental delay, ataxia, episodes of paroxysmal laughter and brachiocephaly — was studied with single-photon emission tomography. Hypoperfusion found in the left frontal and left temporoparietal regions can provide insights into the functional cerebral pathology, which may be due to a disturbance of the developmental process related to a chromosomal abnormality. Correspondence to: K. Gücüyener     

Single-photon emission tomography of a computerised model of pulmonary embolism

Planar pulmonary scintigraphy is currently the standard investigation for the diagnosis of pulmonary embolism. There are a number of problems with the technique, particularly in patients with an intermediate scan report under the PIOPED criteria. The technique is also under threat from the increasing use of spiral CT angiography. A putative improvement may be gained by use of tomography. The incremental value of tomography over planar studies was therefore evaluated in a virtual model of pulmonary scintigraphy. A model of the segmental anatomy of the lungs was developed from computed tomography, cadaveric human lungs and available anatomical texts. Counts were generated within the phantom by Monte Carlo simulation of photon emission. Eighteen single segmental lesions were interspersed with 47 subsegmental defects and displayed on an Icon reporting station. These were presented in the transaxial, sagittal and coronal planes to four experienced reporters to obtain assessment of defect size. Planar studies of the same defects were displayed to the same observers in the standard eight views with a normal study for comparison. With planar studies, the accuracy of estimation of defect size was 51% compared with 97% using tomographic studies. Defects in the medial basal segment of the right lower lobe were not identified in planar studies but were easily seen by all observers in the tomographic study. It is concluded that there is marked improvement in the accuracy of determination of defect size for tomographic studies over the planar equivalents. This is especially important in the lung bases, the most common reported site of pulmonary emboli. Tomography permits visualisation of defects in the medial basal segment of the right lung, which are not seen in planar studies. Received 5 March and in revised form 1 June 1999     

Transmission scanning in emission tomography

Attenuation correction in single-photon (SPET) and positron emission (PET) tomography is now accepted as a vital component for the production of artefact-free, quantitative data. The most accurate attenuation correction methods are based on measured transmission scans acquired before, during, or after the emission scan. Alternative methods use segmented images, assumed attenuation coefficients or consistency criteria to compensate for photon attenuation in reconstructed images. This review examines the methods of acquiring transmission scans in both SPET and PET and the manner in which these data are used. While attenuation correction gives an exact correction in PET, as opposed to an approximate one in SPET, the magnitude of the correction factors required in PET is far greater than in SPET. Transmission scans also have a number of other potential applications in emission tomography apart from attenuation correction, such as scatter correction, inter-study spatial co-registration and alignment, and motion detection and correction. The ability to acquire high-quality transmission data in a practical clinical protocol is now an essential part of the practice of nuclear medicine. Received: 19 February 1998 / Accepted: 19 March 1998     

Phantom evaluation of simultaneous thallium-201/technetium-99m aquisition in single-photon emission tomography

This study investigated downscatter effects in cardiac single-photon emission tomographic studies with simultaneous thallium-201/technetium-99m acquisition, and evaluated a previously proposed subtraction technique for downscatter compensation. Ten studies were carried out with different defect sizes and locations and varying activity distributions using four energy windows: 70±10% keV, 140±10% keV, 100±10% KeV, and 103±16% keV. The subtraction technique used the 100 or 103-keV data to remove scattered^99mTc counts from the 70-keV data. The size and contrast of infarcts in the dual-isotope 70-keV image were artificially decreased compared to those in the 140-keV image, caused by scattered^99mTc counts that were comparable to the primary²⁰¹T1 counts in the 70-keV window. The subtraction technique produced larger defects and more heterogeneous activity in the myocardial wall in dual-isotope 70-keV images compared to the corresponding²⁰¹T1on-ly images. These artifacts were caused by the markedly different spatial distributions of scattered^99mTc counts in the 100-keV (or 103-keV) window as compared with the 70-keV window. It is concluded that scattered^99mTc photons may cause overestimation of ischemia and myocardial viability in simultaneous dual-isotope patient studies. The proposed subtraction technique was inaccurate and produced image artifacts. Adequate downscatter compensation methods must be developed before applying simultaneous²⁰¹Tl/^99mTc acquisition in clinical practice.     

Prognostic value of single-photon emission tomography in acute ischaemic stroke

Single-photon emission tomography (SPET) is widely used in the investigation of acute stroke. We investigated the relationship between SPET data and functional outcome in a large group of acute stroke patients. One hundred and eight patients underwent cerebral computed tomography (CT) and technetium-99m hexamethylpropylene amine oxime SPET after acute ischaemic stroke. We categorised the clinical presentation according to the Oxford classification of acute stroke. Outcome was measured 1 year after stroke using mortality and the Barthel Index for survivors. SPET scans were interpreted without reference to the clinical data using a semi-automatic technique. Three experienced observers determined the presence of luxury perfusion using suitably scaled SPET images in conjunction with the CT scan. Both SPET volume and severity of deficit were significantly negatively correlated with Barthel Index at 1 year (r _s=–0.310,P<0.0001, andr _s=–0.316,P<0.0001 respectively). In patients scanned with SPET within 16 h of stroke onset, the correlations were more strongly negative (r _s=–0.606,P<0.0001, andr _s=–0.492,P<0.005 respectively). Luxury perfusion was not associated ( ²=0.073,df=1,P=0.79) with good functional outcome (Barthel score 60). Stepwise logistic regression identified Oxford classification, total deficit volume and patient's age as significant predictors of functional outcome. Overall predictive accuracy was 72%. Predictive accuracy was better in patients who received SPET within 16 h of stroke onset. SPET provides useful information about the functional outcome of acute stroke at 1 year. However, the accuracy of prediction decreases the longer SPET is delayed. Prognostication using SPET in combination with clinical assessment and other investigations may also be considered.     

A study of myocardial muscarinic receptors in streptozotocin-induced diabetic rats using iodine-123 N-methyl-4-iododexetimide

In previous studies we have shown that iodine-123 N-methyl-4-iododexetimide ([¹²³I]MIDEX) is a suitable single-photon emission tomography radiotracer for the characterisation of myocardial muscarinic acetylcholine receptors (m-AChR) in the normal state. It has been demonstrated that m-AChR are altered as a consequence of diabetes. The aim of the present study was to examine myocardial m-AChR density using [¹²³I]MIDEX in streptozotocin (STZ)-induced diabetic rats. In vitro binding experiments were conducted on left and right ventricle and atrium homogenate membranes of 1-week, 5-week and 10-week STZ-induced diabetic and aged-matched normal rats. The m-AChR densities (B _max values), as determined by saturation experiments with [¹²³I]MIDEX, revealed no difference in left and right ventricles or atrium in 1-week and 5-week STZ-diabetic rats when compared with normal rats. However, the 10-week STZ-diabetic group revealed a 39% (P<0.001) decrease in m-AChR density in atrium with no change in left and right ventricles. The equilibrium dissociation constant (K _d values) was similar in all groups. In vitro binding autoradiography revealed a 40% decrease in m-AChR density in atrium in the same 10-week diabetic rats. No statistically significant difference was found in 1-week and 5-week diabetic rats compared with normals. Ex vivo autoradiography showed a 50% decrease in [¹²³I]MIDEX uptake in atrium in 5-week diabetic rats and a 60% decrease in 10-week diabetic rats. These results demonstrate the ability of the single-photon agent [¹²³I]MIDEX to measure in vitro and ex vivo alterations in myocardial m-AChR density observed in STZ-induced diabetic rats. Received 16 November and in revised form 16 February 1999     

~(99m)Tc-MDP骨显像动态观察珊瑚羟基磷灰石人工骨修复骨干缺损

目的：应用核素骨显像观察不同骨移植物对实验动物骨干缺损修复的动态过程，评价术后不同时期移植骨成活状态。材料与方法：用ＲＯＩ方法定量对比计算三种材料植入区和正常骨区放射性浓集比值。结果：Ａ组（单纯人工骨组）６．０１；Ｂ组（红骨髓复合人工骨组）７．９５；Ｃ组（自体移植骨组）５．７７。结论：单纯人工骨组和自体移植骨组植入后成骨代谢无显著差异，加入自体红骨髓的复合工人骨组移植区成骨代谢明显优于前两组，成骨代谢最旺盛期为２～８周。