[^11C] CFT and [^11C] raclopride images obtained by positron emission tomography (PET) are used to evaluate pre-synaptic dopamine transporter availability and post-synaptic dopamine D2 receptor binding, respectively. A combined study with these tracers is useful for the differential diagnosis of Parkinson's disease. We generated three-dimensional (3D) animations of striatum PET images for the diagnosis of Parkinson's disease. Brain images of a normal subject and a typical Parkinson's disease patient with [^11C] CFT and [^11C] raclopride were obtained using a PET camera. Three-dimensional animations were generated from serial maximum intensity projection (MIP) images created by gradually changing the projection angle. Furthermore, the striatum images extracted from brain data were superimposed over a brain surface magnetic resonance (MR) image that was created by the volume-rendering method, and 3D animations were similarly generated. The present 3D animations were clinically useful for the differential diagnosis of brain diseases, because we were able to observe distributions of [^11C] CFT and [^11C] raclopride from any angle and to grasp at a glance the regional differences of distributions in reference to anatomical landmarks.
Objective: Both the segmented attenuation correction (SAC) method and post-injection transmission scanning are useful and widespread in clinical whole-body FDG-PET studies. The SAC method usually accomplishes smoothing of the transmission data. This calculation segments a μ-map into three degrees (lung, soft tissue, and bone) of attenuation coefficient. This method is used to reduce transmission scan time without deteriorating the quality of PET images. However, the SAC method has a tendency to underestimate the attenuation coefficient, resulting lower detectability for lung field mass lesions. We therefore evaluated the quantitative accuracy of the SAC method using transmission scanning and emission scanning data in a phantom study. Methods: A dedicated 3D PET scanner, the Siemens ECAT EXACT HR+, was used to scan images of two types of phantoms, a spherical phantom (Japan Radioisotope Association phantom) and a cylindrical phantom (20 cm in diameter). We evaluated differences between transmission images (μ-map) of the SAC method and measured attenuation correction (MAC)method, these two kinds of attenuation-corrected emission data (emission + SAC method, emission + MAC method), and emission data only (without attenuation correction). Results: In the μ-map, recovery coefficient (RC) values at 10 mm in diameter were 0.27 and 0.00 in the MAC and SAC methods, respectively, in the spherical hot area. For the emission data, the emission + SAC method and emission + MAC method showed almost the same RC values for all sizes of hot area diameter. The SAC method, however, resulted in 20% underestimation for all sizes of hot area diameter as compared with the MAC method. Conclusion: In pulmonary mass lesions, it is necessary to correct for the partial volume effect in quantitative PET measurement. However, from our data, the SAC method is not appropriate for partial volume effect correction.
Quantitative gated SPECT(QGS)software has been reported to demonstrate inaccurate edge detection in the left ventricular chamber in hypertrophic cardiomyopathy patients. In this study we developed a method to calculate left ventricular volume (LVV) and left myocardial volume (LMV) from gated SPECT data using a newly developed edge-detection algorithm, and we compared it with the QGS method of calculating LVV and LMV in a phantom study. Our method gave more accurate measurements LVV and LMV whereas the QGS method underestimated LMV. Compared with QGS LVV and LMV, our method yielded better results in the phantom study.
A synchronized sampling method (SSM) was developed for the study of voluntary movements by combining the electrocardiographic (ECG) gating method with an external triggering device, and four-dimensional magnetic resonance imaging (4D-MRI) at a rate of 30 frames per second was accomplished by volumetric imaging with the SSM. This method was first applied to the motion imaging of articulatory organs during repetitions of a Japanese five-vowel sequence, and the dynamic change in vocal tract area function was demonstrated with sufficient temporal resolution. This paper describes the methodology, applicability, and limitations of 4D-MRI with the SSM.
In imaging using contrast-enhanced three-dimensional magnetic resonance angiography (CE-3DMRA), optimizing the delay time from the start of intravenous injection of contrast medium to the start of scanning has generally been an important concern when obtaining blood vessel images of good contrast. Recent methods of mechanically assessing the attainment of contrast medium injection include Smart-Prep and others. Another method is the Test Bolus, in which a small amount of contrast medium determines the timing of scan start, in quest of the time intensity curve. Because these methods are not necessarily satisfactory, the corrected method is used in clinical cases. In terms of how scan timing affects blood vessel depiction, no study has examined pulsatile flow, which is carried out by simulation. On the other hand, there are reports on data filling of k-space using imitation blood vessels on a computer and simple experimental equipment. This research examined experimentally blood vessel depiction according to scan timing and the diameter of blood vessels by using a systemic circulation simulator that incorporated hemodynamic circulation in which pulsatile flow is the same as that of a human body, using an artificial heart developed especially for MRI. It is thought that scan timing in CE-3DMRA affects the depiction of blood vessels for which the diameter of the blood vessel differs from the experimental result. Phase-encoding k-space data filling is the contrast-to-noise ratio (CNR) of each blood vessel irrespective of sequential and centric k-space ordering. The timing shift phenomenon, in which a blood vessel is so thin that the scan timing is overdue and shows a relatively high value, can occur. Moreover, that scan timing affects not only the diameter of a blood vessel but also depiction of the narrowing of a stenotic blood vessel or a branch blood vessel was demonstrated clinically and experimentally. Therefore, blood vessel depiction changes with scan timing, and it is clinically important to determine the time of arrival of contrast medium and the duration of the enhancement effect in quest of the time intensity curve by test bolus when clearly describing the target blood vessel.
The progress of three-dimensional (3D) magnetic resonance angiography used in combination with contrast medium (CE-MRA) has been remarkable. Currently, angiography aims at improvements in time resolution without sacrificing spatial resolution. We conducted a basic study of 3D differential rate k-space sampling (DRKS)in which the slice direction of the k-space is divided into two or more areas, the echo data near zero encoding is sampled by a higher time resolution than data in other areas, and reconstruction is done within a short time. This technique involved a problem in which ghost artifacts occur easily when the concentration of contrast medium changes extremely or when signal intensity changes suddenly. This is probably due to a difference in the time to sample data between the low- and high-frequency areas. When we used DRKS to grasp these characteristics, however, it was useful because it allowed reconstruction with an extremely high time resolution.
We evaluated the fitting scan technique for CE-3dMRDSA, and found common ground that determines spatial resolution and time resolution (slab thickness and partition number). We also examined the relation between appearance and time resolution (volume of contrast medium and injection speed). To obtain good image contrast, the volume of contrast medium needs to be at least 7 ml and suitable for an injection speed of 3-5 ml/sec. However, when we increased the volume of contrast medium and decreased injection speed, changes in MRDSA images with time became worse. The measure of the bolus with contrast medium was found to determine image contrast. When contrast medium is injected earlier, it circulates earlier within the brain. If the scan time is not short enough, it is not possible to observe changes in MRDSA images. And when spatial resolution is improved, time resolution becomes worse. Therefore, it is important to find the point of compromise between spatial resolution and time resolution. If we look for anterior MIP images, the CNR in the spatial resolusion didn't change, when the slice thickness is more than 3 mm. Because, the partial volume effect decide the image contrast. However, unless the view is from the front, slice thickness influences spatial resolution. Therefore, when we view MIP images from the lateral direction, slice thickness must be set at less than 2 mm. Results indicated that, in CE-3dMRDSA with the fitting technique, slice thickness should be less than 3 mm, partition number 16-20, slab thickness 48 mm, contrast medium volume 7-10 ml, and injection speed 3-5 ml.
The optimal imaging conditions for 3D brain surface imaging by magnetic resonance imaging (MRI) and multi-slice CT were investigated. Visualization of the sulci, gyri, and veins on the brain's surface was also compared between 3D surface images acquired using multi-slice CT and conventional single-slice CT and MRI. Various imaging parameters, including slice thickness, dose, and matrix size, were evaluated using our original brain surface phantom and longitudinal direction evaluation phantom as well as images obtained from healthy volunteers. Subjects of the clinical study were patients with arteriovenous malformations and brain tumors who underwent CT-angiography at the same time as MR-angiography. The quality of 3D images of the brain surface is most strongly influenced by partial volume effects related to slice thickness. In multi-slice CT, a slice thickness of 0.5 mm can be employed to minimize the partial volume effect, providing results that are far superior to those that can be achieved by conventional single-slice 3D-CT. In addition, the excellent S/N of multi-slice CT permits the veins on the brain's surface to be clearly visualized without the use of contrast medium. With regard to visualization of the sulci and gyri, although some problems remain to be overcome, multi-slice CT was found to be equivalent to 3D surface imaging using MRI.
The purpose of this study was to determine the usefulness of three-dimensional (3D) MR imaging of brain tumors for surgical planning. Sixty-nine patients with various tumors of the brain were included in the present study. Using a volume-rendering (VR) method on an independent workstation, 3D-MR images were obtained with the fast-SPGR sequence after Gd-DTPA administration. VR images could show an exact relationship between the surface of the brain and major vessels. However, in patients with deeply located tumors, VR images did not necessarily provide sufficient information as to the relationship between the tumor and vessels. In combination with a surface-rendering method, 3D-MR imaging could demonstrate the exact relationships among the tumors, major vessels, and surface of the brain. In tumors without contrast enhancement, this method was able to show 3D images of tumors with surrounding structures. For neurosurgeons, 3D-MR images were useful for understanding the surface anatomy and surrounding structures of the tumors prior to surgery. These images were also helpful in explaining the condition of the disease to patients and their families.
When processing head MRA images, threshold values are automatically established using the MIP method, resulting in a high degree of reproducibility. As a result, two different individuals can produce highly comparable images. In addition, the MIP method is reportedly effective for depicting fine vessels. However, since information other than maximum values is ignored by the MIP method, data contained in original MRA images are not optimally utilized. The results confirmed that much of the information contained in original MRA images could not be seen on MIP processed images. In many cases, low-threshold processing was useful for depicting fine vessels and arterioles that could not be seen on MIP-processed images.
This paper describes an integrated methodology that addresses the operation of 3D imaging and measurement for the diagnosis and surgical operation of breast cancer. The main system for breast CT imaging used a multi-slice CT scanner and 3D-workstation. The clinical sequence was performed in three phases with non-contrast and biphasic contrast-enhanced studies that were performed with multi-slice helical CT scanning. Acquired DICOM images were directly sent to the 3D workstation that implemented our developed functions. Four types of transfer functions (mammary skin, vessel, lymph node, and tumor) were set based on region-of-interest (ROI) measurements. After that, two types of segmentation were prepared with volumetry and measurement of the size of breast cancer. Batch processing for 3D visualization and the measurement of breast tumors was helpful for diagnosis and surgical planning.
To investigate the angioarchitecture of cerebral aneurysms, we studied various opacity curves to select specific volume data of CT and MR angiograms from the opacity charts of CT density or MR signal intensity distribution. We developed the method of transluminal imaging of CT and MR angiograms; the vessels and aneurysms were depicted transluminally through spaces between the rings of the vessel walls. Two cases of unruptured cerebral aneurysms were studied by transluminal imaging of three-dimensional CT and MR angiograms. The technical aspects of transluminal imaging and characteristics of volume data, obtained by CT and MR angiograms, were discussed.
In recent years, laparoscopic surgery has attracted attention as a minimally invasive type of surgery because of the small surgical wounds and early recovery it provides. We carry out this technique on the basis of volume data that we make use of in multi-slice CT imaging technology in laparoscopic nephrectomy by the retroperitoneal approach, and we have created CT virtual laparoscopy by virtual endoscopic display as an intra-operative navigatior with an image analysis system. We provide information on detailed vascular anatomy to form intra-operative images that act as similar support images. With the provision of this volume data, we consider virtual endoscopic display the most suitable method for surgery. When we perform virtual laparoscopy, we simulate the insertion point and angle, the order of vascular structures and their locations, the number of arteries and veins, and their bifurcation points and ligation points in conjunction with the surgeon prior to operation. As the branch patterns of the renal artery are varied, perioperative confusion and surgical mishaps can be avoided through the information that is provided beforehand. Thus surgery is more accurate and proceeds more smoothly, because the surgeon has accurate anatomical information. In addition, the time required for surgery is decreased, reducing risk and the possibility of complications.
Rotational three-dimensional digital subtraction angiography (3D-DSA) is very useful for interventional neuroradiology, especially in the endovascular therapy of cerebral aneurysms. However, pseudo-stenosis artifact on the vessel, which runs vertically to the rotational axis, was observed clinically. In this study, this artifact was confirmed in an experiment with 4.5-millimeter diameter vessel phantoms. The attenuation of the phantom at each degree of exposure (44 directions) was measured on the workstation (DSA pixel value). DSA pixel values were plotted from data of 10, 20, 30, 40, and 50 millimeter lengths, respectively. The saturated DSA pixel value of tangent projection on phantoms of 30 millimeters or more in length was observed. This phenomenon induces pseudo-stenosis artifact on 3D-DSA. The maximum reduction in the diameter of the phantom was 27.4% on the length of 50 millimeters. We confirmed that the two-dimensional data vertical to the rotational axis were inaccurate when a straight-coursed, long, segmented vessel was present. Under this special condition, vessels on 3D-DSA were displayed as smaller than their actual diameter.