Transtomography for implant placement guidance in non-invasive surgical procedures

OBJECTIVES: To illustrate the use of transtomography for the placement of implants using a radiopaque radiographic guide and to evaluate the accuracy of transtomography. METHODS: The study included 11 implants inserted with minimally invasive procedures. Pre-operative, intraoperative and post-operative examinations were performed with a ProMax panoramic unit implemented with transtomographic technique (Planmeca Oy, Helsinki, Finland). At each implant site, cross-sectional and longitudinal intraoperative transtomograms were taken through a radiopaque reference guide to control and adjust the drilling axis. The effective axis on post-operative transtomograms was compared with the planned axis correction estimated on intraoperative images. Radiopaque guides, used as the gold standard, were measured on intraoperative cross-sectional slices to evaluate image distortion. RESULTS: Intraoperative transtomograms, with the reference guide inserted in the bone, gave clear images of the cortical plates and accurate information of drilling length and axis, which allowed the surgeon to adjust pilot drilling axis in 6 sites (54.5%) out of 11 sites, including sites with narrow bone ridges. The implant axis on the post-operative tomogram compared with the planned axis correction showed an angle difference ranging from 0.8 degrees to 3.4 degrees. The image distortion on cross-sectional slices ranged from 0.03 mm to 0.52 mm, resulting in a distortion ratio ranging from 0% to 6% when expressed in percentages. CONCLUSIONS: Transtomographic examination performed with a radiographic reference guide during implant surgery can provide the necessary and accurate information for implant placement. Transtomography distortion appears to be less important than in other conventional tomographic systems and comparable with CT scan distortion.     

Image distortion in narrow beam rotation radiography. A mathematical analysis

A general mathematical analysis of the image distortion in narrow beam rotation radiography has been performed. Distortion effects are often evident in panoramic images exposed in clinical practice. It is found that in spite of this general experience panoramic images, exposed with the aid of a rotating narrow beam, are reliable for ordinary clinical demands when the object morphology is to be assessed. This statement is valid provided that the object has been properly positioned at the exposure.     

Triple images on panoramic radiographs.

OBJECTIVE: To explain the formation of triple images on panoramic radiographs. METHODS: A metal test object was placed in defined positions in relation to movement path of a panoramic X-ray beam. RESULTS: The test object was portrayed once, twice or three times with varying degrees of distortion depending on its location. Triple images were formed when the test object was located in a specific diamond-shaped area distal to the path of the rotation centre of the X-ray beam. CONCLUSIONS: The formation of triple images on panoramic radiographs can be explained on the basis of known projection geometry.     

Digital tomosynthesis: technique for electronic reconstructive tomography

A technique is described for obtaining tomographic images through retrospective reconstruction of digital data. The apparatus used for this technique, called digital tomosynthesis consists of a linear tomographic x-ray machine that has been modified by the addition of a fluoroscope and TV system, a video disk recorder, an analog-to-digital converter, and a small computer for data processing and manipulation. Video frames are collected and stored during a single tomographic sweep. The stored data are then digitized and retrospectively processed in the computer for reconstruction of any desired tomographic plane within the body. The major advantages of DTS include short patient study time, low radiation dose compared with conventional tomography, the ability to enhance the digitized image through manipulation of window and level display, and the applicability of this technique to dynamic studies such as angiotomography. Phantom studies show good diagnostic quality of the resulting images, and preliminary vascular studies in dogs indicate the clinical potential of this technique for use in digital subtraction angiotomography.     

A novel panoramic machine for photofluorography

OBJECTIVE: To describe the main features of a prototype panoramic X-ray machine modified for photofluorography. METHODS: The prototype PTM 2001 (Asahi Roentgen, Kyoto, Japan) consists of a conventional panoramic machine with a modified X-ray generator and incorporating a 9-inch image intensifier and a photofluorographic camera. RESULTS: The photofluorographic panoramic radiograph is reduced in size by 60% compared with conventional images. Using 10 cm x 45.7 m photoradiographic film 250 panoramic images can be continuously obtained. Examination time is shorter since cassette changes are not necessary. The radiation dose-in-air, measured in front of the secondary collimator, is 174 muGy. CONCLUSIONS: The advantages of the photofluorographic panoramic radiography include cost economy, shorter examination time and lower radiation exposure.     

Use of a new myocardial centroid for measurement of regional myocardial dysfunction by electron beam computed tomography: comparison with technetium-99m sestamibi infarct size quantification

RATIONALE AND OBJECTIVES: The study compared the performance of conventional endocardial and epicardial centroid algorithms with the new "myocardial" centroid algorithm in patients with anterior myocardial infarction. "Floating" endocardial or epicardial centroid algorithms, commonly used in tomographic imaging methods to assess regional motion, may misrepresent left ventricular regional myocardial function in the presence of markedly asymmetric left ventricular contraction. METHODS: A new centroid algorithm based on regional myocardial mass distribution was tested in 29 patients with a first anterior myocardial infarction and was compared with conventional centroid algorithms. Direct comparisons in 60 equal sectors at one midventricular level per patient were performed between electron beam computed tomography and technetium-99m sestamibi single-photon emission computed tomography. The thresholds of regional myocardial function used to define infarction were varied for regional ejection fraction from 20% to 40% and for regional wall thickening from 0 to 4 mm. Regression and Bland-Altman analysis were used to compare infarct size by regional myocardial function with infarct size by sestamibi single-photon emission computed tomography. RESULTS: The new myocardial centroid showed the least shift toward infarcted myocardium from diastole to systole and had the highest amplitudes of the measurement curves for regional ejection fraction and regional wall thickening. The optimal regional myocardial function thresholds for each centroid algorithm for regional ejection fraction were endocardial, 30% (R = 0.62; mean difference to sestamibi, -0.5% +/- 22.1% tomographic infarct size points); epicardial, 30% (R = 0.79; mean difference, 2.2% +/- 13.1% tomographic infarct size points); and new myocardial, 25% (R = 0.88; mean difference, -0.6% +/- 9.5% tomographic infarct size points). The optimal thresholds for regional wall thickening were endocardial, 1 mm (R = 0.70; mean difference, -2.2% +/- 14.3% tomographic infarct size points); epicardial, 1 mm (R = 0.78; mean difference, -4.6% +/- 12.7% tomographic infarct size points); and new myocardial, 2 mm (R = 0.71; mean difference, 2.1% +/- 14.1% tomographic infarct size points). The best agreement (R = 0.88) between electron beam computed tomography infarct size and sestamibi single-photon emission computed tomography infarct size was achieved with regional ejection fraction and the new myocardial centroid algorithm. CONCLUSIONS: In asymmetrically contracting left ventricles, the new myocardial centroid algorithm is superior to conventional methods for tomographic analysis of regional myocardial function.     

Tomoscopy: dynamic layer imaging without mechanical movements

A tomographic system in which electronic movement of the x-ray source and the image receptor replace the mechanical movement of conventional tomography has been constructed and tested. Because the system permits very short, rapidly repeated exposures, viewing by television provides real-time fluoroscopic tomography, termed tomoscopy. Further, electronic adjustment of tomographic layer height permits rapid direct search for the optimum layer. The system requires no more than conventional fluoroscopic radiation levels and resolves 3 line pairs per millimeter (LP/mm) in the televised image and 4 LP/mm in the spot film images. It offers rapid, highly customized, high-resolution tomography under direct fluoroscopic control. Precise percutaneous biopsy with integrated needle-controlled equipment and tomography of contrast-filled blood vessels incorporating digital subtraction principles are theoretic possibilities.     

A new sonographic technique for assessing carotid artery disease: extended-field-of-view imaging

We describe a new sonographic technique, extended-field-of-view imaging, and its clinical application for carotid artery disease. The technique identifies identical structures on two successive images for position registration to make a panoramic image in real time without position sensors. In 39 of 41 subjects, this technique provided high-quality panoramic images that could not be obtained with conventional real-time sonography, and made findings in the carotid artery more interpretable.     

Pulmonary nodules: detection of calcification by linear and pluridirectional movement in tomographic study

Calcification within solitary pulmonary nodules (1-2 cm range) was demonstrated by conventional tomography in a group of 20 patients. Each patient had a combined tomographic examination consisting of 15 degrees linear movement followed by 34 degrees hypocycloidal movement. Linear tomography was superior to pluridirectional tomography in 19 cases for visualization of calcium within the nodule. The results are attributed to differences in contrast sensitivity and "blur" phenomena between the two tomographic movements. This study, although comparing a specific linear movement with a specific pluridirectional movement, provides insight into the differences between tomographic techniques for a given task.     

电子束CT血管造影评价冠状动脉狭窄

目的:探讨电子束CT(EBT)血管造影评价冠状动脉狭窄的价值.材料和方法:分析56例经EBT血管造影和常规冠状动脉造影(CAG)检查的资料,将冠状动脉各支分成13个节段与相应CAG结果逐一对照,并进行统计学分析.结果:679个≥2mm的冠状动脉节段中,EBT可评价562个,无法评价117个.EBT对各支冠状动脉的评价准确性依次为左主干、前降支和右冠;对各节段的评价以近段的敏感性、特异性和阴性预测值最高;对不同程度狭窄的评价以＞75%狭窄的诊断最为可靠.此外对正常冠状动脉的诊断准确性也较高,为88.5%.结论:EBT血管造影对评价冠状动脉近段狭窄、重度狭窄和正常血管有很高的价值,可作为CAG术前筛选的常规无创性检查方法.     

Positron tomographic imaging of the liver: 68 Ga iron hydroxide colloid

A new radiopharmaceutical, 68Ga ion hydroxide colloid, for hepatic imaging by positron emission tomography was prepared from the eluate of a 68Ge-68Ga solvent extraction generator. In rats, 84% of the administered dose of colloid localized in the liver and 4.6% accumulated in the spleen. Initial imaging studies in normal dogs showed close correspondence of the findings by positron tomography and transmission computed tomography. Emission tomography with 68Ga-colloid was performed in 10 patients with hepatic metastases demonstrated by conventional 99mTc sulfur colloid scintigraphy. All focal defects noted on the conventional scintigrams were easily identified and generally were seen more clearly by positron tomography. In one patient, additional lesions not identified on the initial 99mTc sulfur colloid images were demonstrated. The positron tomographic images were compared with those obtained by transmission computed tomography in seven patients; the two studies showed comparable findings in five patients, whereas positron tomography more clearly showed multiple lesions in two. Our results suggest that positron emission tomography is a suitable technique for obtaining high contrast, cross-sectional images of large abdominal organs.     

Cone beam CT and conventional tomography for the detection of morphological temporomandibular joint changes

OBJECTIVE: To compare the diagnostic accuracy of cone beam CT images with conventional tomographic images for the detection of morphological temporomandibular joint (TMJ) changes. METHODS: 80 dry human skulls were scanned using a NewTom 3G scanner and lateral and frontal reconstructions of the right and the left TMJs were performed. In addition, lateral and frontal cross-sectional tomograms of the skulls' TMJs were obtained in a Cranex Tome unit with Digora storage phosphor plates. Naked-eye inspection of the TMJs performed by three observers served as the gold standard for the true presence of morphological changes. The mandibular fossae were excluded from the study due to few changes in this joint component. The NewTom and the conventional tomographic images were examined by three independent observers using a binary scale for the presence of morphological changes in the condyle (flattening, defects and osteophytes) and the articular tubercle (flattening and defects). The accuracy for the different types of changes in relation to the condyles and the articular tubercles was expressed as sensitivity and specificity values, whereas the diagnostic accuracy for a general assessment including all changes in both joint components was expressed by the sum of cases where the gold standard and the radiographic scores were not identical (absolute difference). Differences between the two radiographic modalities were tested by paired t-test. RESULTS: Detection of the various types of morphological changes in relation to the condyle and the articular tubercle assessed separately resulted in no significant differences between the two radiographic modalities, with the exception of bone defects in the articular tubercle examined on frontal views alone where the specificity with tomography was significantly higher than with cone beam CT. Detection of all morphological changes in relation to both the condyle and the articular tubercle showed a significantly higher accuracy with tomography than with cone beam CT using lateral views alone, but there was no significant difference between the two modalities using frontal views alone and lateral and frontal views in combination. CONCLUSION: In general, no significant differences in diagnostic accuracy for the detection of bone changes in the condyle and in the articular tubercle were found between cone beam CT images and conventional tomograms.     

The accuracy and reliability of radiographic methods for the assessment of marginal bone level around oral implants

OBJECTIVES: To determine the accuracy and reliability of radiographic methods for assessment of the marginal bone level around oral implants in human cadavers. METHODS: In three human cadavers two implants were placed according to the Instruction Manual for the Br?nemark System. One implant was installed in the canine and one in the premolar region of the left mandible. For each implant, conventional and digital intra-oral paralleling radiography were performed. Digital images were printed with a Kodak 1200 Distributed Medical Imaging printer on blue transparent film, glossy and plain paper. Furthermore, digital scanographic, panoramic and tomographic images were taken with the Cranex Tome multimodal X-ray unit and printed on Agfa Drystar TM 1 B transparent films. All images were evaluated by five dental specialists. Data were statistically compared with real measurements of the marginal bone level on the human cadavers, performed by the same group of observers. Intra- and inter-observer variability were determined. RESULTS: Digital intra-oral images on glossy paper showed the smallest absolute difference between real and measured bone level, followed by digital intra-oral images on film and on plain paper, conventional intra-oral images on analogue film, panoramic, scanographic and tomographic images on film. The difference between real and radiographic measurements was not statistically significant (P>0.05) for all radiographic techniques. Intra- and inter-observer reproducibility was high for all techniques. CONCLUSIONS: The selected imaging techniques showed an acceptable accuracy for peri-implant bone level measurements with an overall error of less than 0.5 mm. Intra-oral images showed the smallest absolute differences.     

Quality of digital pre-implant tomography: comparison of film-screen images with storage phosphor images at normal and low dose

OBJECTIVES: The aim of this pilot study was to compare the image quality of a storage phosphor system with that of conventional film-screen in pre-implant conventional tomography, and to test the influence of radiation dose on image quality in the storage phosphor system. METHODS: Cross-sectional conventional tomographic images (Scanora) technique) were obtained on 11 patients with film-screen and with storage phosphor image plates (Digora) PCT) at normal and low doses. Ten observers graded the visibility of anatomical structures of importance for implant planning. A three-step rating scale was used, where -1 =worse, 0=equal and 1=better than the reference image. RESULTS: Although image quality was graded as equally good in the majority (59%) of images, the storage phosphor system scored significantly lower than film-screen (-0.37 vs 0.00, respectively) for all the images. Low dose storage phosphor images were rated significantly lower (-0.21) than normal dose images (0.00). CONCLUSIONS: In the majority of patients, anatomic structures of importance for implant planning are visualized equally well on storage phosphor and film-screen images. However, where differences do exist, storage phosphor images score lower than film-screen images. Dose reduction in the storage phosphor system had a negative influence on image quality.     

电子束CT血管造影对冠状动脉内支架开通的评价

目的 :探讨电子束CT(EBT)血管造影在冠状动脉支架的定位及评价支架开通中的应用价值。方法 :5 6例患者分别于冠状动脉造影术后 1月～ 6年接受EBT检查。采用单层序列平扫及增强扫描、单层或多层血流序列扫描。三维重建采用最大密度投影法 (MIP)及曲面重建法 (CPR) ,三维结果均与手术结果对照 ,其中 8例有EBT检查后的造影结果。结果 :86支冠状动脉于造影中放置 12 0枚支架 ,EBT准确定位 118枚 (98.3% )。其中 4 0支显示通畅 ,通畅率 4 6 .5 % ;37支血管狭窄 ,狭窄率 4 3% ;9支冠状动脉支架内闭塞。结论 :①EBT血管造影及三维重建可准确定位冠状动脉内支架并判断支架开通 (通畅、狭窄、闭塞 )的情况 ;血流分析可提供支架远端血管的血流曲线及定量数据 ,是评价支架开通重要的定量补充诊断 ;②EBT可作为支架置入术后长期随访的无创检查方法 ,可部分减少冠状动脉造影有创复查的次数 ;③限度 :无法准确评价狭窄的程度     

Modern dental imaging: a review of the current technology and clinical applications in dental practice

A review of modern imaging techniques commonly used in dental practice and their clinical applications is presented. The current dental examinations consist of intraoral imaging with digital indirect and direct receptors, while extraoral imaging is divided into traditional tomographic/panoramic imaging and the more recently introduced cone beam computed tomography. Applications, limitations and current trends of these dental “in-office” radiographic techniques are discussed.     

Analysis of the accuracy of linear measurements obtained by cone beam computed tomography (CBCT-NewTom)

OBJECTIVES: The conical beam computed tomography (CBCT) technique presents an innovation of tomographic imaging systems and subsequent volumetric image reconstruction for dentistry. When compared with other methods of tomographic imaging CBCT is characterized by rapid volumetric image acquisition from a single low radiation dose scan of the patient. The NewTom (NewTom 9000; Quantitative Radiology, Verona, Italy) is an example of such a CBCT machine dedicated to dental and maxillofacial imaging, particularly for surgical and/or prosthetics implant planning in the field of dentistry. The aim of this study was to evaluate the accuracy of the linear measurements obtained in CBCT images using a NewTom. METHODS: Thirteen measurements were obtained in dry skulls (n = 8) between internal and external anatomical sites using a caliper. These were considered as real measurements. Then the dry skulls were submitted to CBCT imaging examinations. Radiographic distance measurements of the same dry skull anatomical sites were made using the NewTom QR-DVT 9000 software of the 2 mm-CTs axial section images and sagittal or coronal reconstructions. The data were compared by paired Student's t-test. RESULTS: The results showed that the real measurements were always larger than those for the CBCT images, but these differences were only significant for measurements of the internal structures of the skull base. CONCLUSIONS: The conclusion of this study is that, although the CBCT image underestimates the real distances between skull sites, differences are only significant for the skull base and therefore it is reliable for linear evaluation measurements of other structures more closely associated with dentomaxillofacial imaging.     

Three-dimensional lithographic model building from volume data sets

Computed tomographic images of a dry human skull and an in-situ knee joint were used to construct solid three-dimensional polymer models using stereolithographic techniques that have been introduced recently into the manufacturing industry. The stereolithographic technique makes use of a computer-steered narrow laser beam to solidify the model within a bath of liquid photocurable polymer. The method does not suffer from the cutting-tool size and path constraints encountered in the more commonly used process of machining the models from a solid block of foam.     

Single-photon emission computed tomography of the normal liver

Single-photon emission computed tomography (SPECT) is a new imaging method that offers the advantage of cross-sectional imaging and improved contrast resolution as compared with conventional planar imaging. Preliminary SPECT studies of the liver for detection of metastatic disease are very promising. However, these studies indicate some potential pitfalls in the interpretation of the normal liver SPECT images. Experience with 58 tomographic studies obtained with a General Electric 400T rotating gamma camera is presented, with special emphasis on the areas of potential misinterpretation and on recognition of the normal anatomy as seen by this technique.