Hiroshi Higashino

Cardiac imaging using 256-detector row four-dimensional CT: preliminary clinical report

PurposeAlong with the increase of detector rows on the z-axis and a faster gantry rotation speed, the spatial and temporal resolutions of the multislice computed tomography (CT) have been improved for noninvasive coronary artery imaging. We investigated the feasibility of the second specification prototype 256-detector row four-dimensional CT for assessing coronary artery and cardiac function.Materials and methodsThe subjects were five patients with coronary artery disease. Contrast medium (40–60 ml) was intravenously administered at the rate of 3–4 ml/s. The patients whole heart was scanned for 1.5 s to cover at least one cardiac cycle during breathholding without electrocardiographic gating. Parameters used were 0.5 mm slice thickness, 0.5 s/rotation, 120 Kv, and 350 mA, with a half-scan reconstruction algorithm (temporal resolution 250 ms). Twenty-six transaxial datasets were reconstructed at intervals of 50 ms.ResultsThe assessability of the coronary arteries in AHA segments 1, 2, 3, 5, 6, 7, 9, and 11 was visually evaluated, resulting in 29 of 32 (90.9%) segments being assessable. Functional assessment was also performed using animated movies without banding artifacts in all cases.ConclusionsThe 256-detector row four-dimensional CT can assess the coronary artery and cardiac function using data during 1.5 s without banding artifacts.

Attenuation correction of myocardial SPECT images with X-ray CT : Effects of registration errors between X-ray CT and SPECT

Purpose: Attenuation correction with an X-ray CT image is a new method to correct attenuation on SPECT imaging, but the effect of the registration errors between CT and SPECT images is unclear. In this study, we investigated the effects of the registration errors on myocardial SPECT, analyzing data from a phantom and a human volunteer.Methods: Registerion (fusion) of the X-ray CT and SPECT images was done with standard packaged software in three dimensional fashion, by using linked transaxial, coronal and sagittal images. In the phantom study, an X-ray CT image was shifted 1 to 3 pixels on thex, y andz axes, and rotated 6 degrees clockwise. Attenuation correction maps generated from each misaligned X-ray CT image were used to reconstruct misaligned SPECT images of the phantom filled with201Tl. In a human volunteer, X-ray CT was acquired in different conditions (during inspiration vs. expiration). CT values were transferred to an attenuation constant by using straight lines; an attenuation constant of 0/cm in the air (CT value=−1,000 HU) and that of 0.150/cm in water (CT value=0 HU). For comparison, attenuation correction with transmission CT (TCT) data and an external γ-ray source (99mTc) was also applied to reconstruct SPECT images.Results: Simulated breast attenuation with a breast attachment, and inferior wall attenuation were properly corrected by means of the attenuation correction map generated from X-ray CT. As pixel shift increased, deviation of the SPECT images increased in misaligned images in the phantom study. In the human study, SPECT images were affected by the scan conditions of the X-ray CT.Conclusion: Attenuation correction of myocardial SPECT with an X-ray CT image is a simple and potentially beneficial method for clinical use, but accurate registration of the X-ray CT to SPECT image is essential for satisfactory attenuation correction.

Quantification of Myocardial Perfusion by Contrast-Enhanced 64-MDCT: Characterization of Ischemic Myocardium

OBJECTIVE Assessment of hemodynamic changes in ischemic cardiac segments at rest using CT has yet to be performed. We hypothesized that variations in subendocardial perfusion during the cardiac cycle might be related to the appearances of ischemia. The purpose of this study was to investigate myocardial perfusion in ischemic segments using contrast-enhanced 64-MDCT. SUBJECTS AND METHODS We performed cardiac MDCT at rest and stress/rest (201)Tl myocardial perfusion scintigraphy (MPS) in 34 patients with suspected coronary artery disease. We reconstructed 2D long- and short-axis cardiac images in diastolic and systolic phases using raw data from coronary CT angiography. The attenuation value (in Hounsfield units) in the myocardium was used as an estimate of myocardial perfusion. We measured the subendocardial intensity of 17 segments according to the American Heart Association classification. Systolic perfusion or diastolic perfusion was calculated by dividing the subendocardial intensity at systole or diastole, respectively, for each segment by the mean value across all segments for each patient. We used stress/rest MPS to evaluate the variation in myocardial perfusion at systole and diastole for the segments diagnosed as ischemic or nonischemic. RESULTS Systolic perfusion for ischemic segments was significantly lower than that for nonischemic segments in 15 of 17 segments. The difference between systolic perfusion and diastolic perfusion in ischemic segments was significantly lower than that in nonischemic segments (14 of 17 segments). There was no significant difference in diastolic perfusion between ischemic and nonischemic segments (15 of 17 segments). CONCLUSION Our results suggest that a pattern of subendocardial hypoperfusion at systole and normal perfusion at diastole characterizes ischemic myocardium.

Demonstration of Acute Myocardial Infarction by Subsecond Spiral Computed Tomography Early Defect and Delayed Enhancement

Case 1. An 85-year-old woman was hospitalized after 3 hours of chest pain and dyspnea. She was diagnosed as having anteroseptal acute myocardial infarction (AMI) from her symptoms and the ECG (elevated ST-T in leads I, aV L, and V1 through V3). She had to wait for emergency coronary angiography (CAG), because another patient with AMI was occupying the catheter laboratory. During her standby status, contrast-enhancement spiral CT was performed (Figure 1a). Total occlusion of the left anterior descending coronary artery (segment 7) was observed by the CAG. Six days after successful direct PTCA, plain and Gd-enhancement T1weighted MRI was performed (Figure 1b). Three days after the PTCA, dual SPECT withTc-pyrophosphate (hot scan) and Tl was performed (Figure 1c). Seven days after the PTCA, serial dynamic spiral CT data were obtained at 50 seconds, 3 minutes, and 8 minutes at injection of the contrast material (1.2 mL/s, 100 mL total) (Figure 2). Case 2. A 49-year-old man presented with chest pain. He was diagnosed as having inferior AMI from his symptoms and the ECG (elevated ST-T in leads II, III, aV F, and V6). CAG demonstrated 99% stenosis of the right coronary artery (segment 4PD). Two days after successful direct PTCA, contrastenhancement spiral CT was performed (Figure 3a). Three days after the PTCA, dual SPECT withTc-pyrophosphate (hot scan) andTl was performed (Figure 3b).Case 1. An 85-year-old woman was hospitalized after 3 hours of chest pain and dyspnea. She was diagnosed as having anteroseptal acute myocardial infarction (AMI) from her symptoms and the ECG (elevated ST-T in leads I, aVL, and V1 through V3). She had to wait for emergency coronary angiography (CAG), because another patient with AMI was occupying the catheter laboratory. During her standby status, contrast-enhancement spiral CT was performed (Figure 1a⇓). Total occlusion of the left anterior descending coronary artery (segment 7) was observed by the CAG. Six days after successful direct PTCA, plain and Gd-enhancement T1-weighted MRI was performed (Figure 1b⇓). Three days after the PTCA, dual SPECT with 99m …

Ischemic “memory image” in acute myocardial infarctio of123I-BMIPP after reperfusion therapy: A comparison with99mTc-pyrophosphate and201Tl dual-isotope SPECT

Ischemic “memory image” is a phenomenon of123I-15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid (BMIPP) in which an area at risk of acute myocardial infarction (AMI), could be detected as a defect in a couple of weeks even after successful reperfusion therapy.The purpose of this study was to clarify the incidence of the ischemic “memory image” of123I-BMIPP in patients with AMI by comparing99mTc-PYP and201Tl dual-isotope SPECT.Materials consisted of 14 patients with successfully reperfused AMI and 20 patients with old myocardial infarction (OMI). All AMI patients underwent PYP/Tl dual-isotope SPECT within 1 week after the onset of AMI, and BMIPP SPECT was performed within 1 week after the PYP/Tl dual-isotope SPECT. The extent and severity of the defect of BMIPP and Tl were visually scored into four grades: 0=no defect to 3=large or severe defect. These scores were compared.PYP positive AMI lesions were concordant with BMIPP defects (13/14). In AMI, both the extent and severity scores of BMIPP were higher than201Tl (p<0.001). Differences (BMIPP-Tl) of extent and severity scores were greater in AMI than in OMI (p<0.001).In conclusion, the ischemic “memory image” obtained by means of the BMIPP is a common phenomenon (13/14) in AMI, and helpful in evaluating the area at risk.

Peri-infarct dysfunction in post-myocardial infarction: assessment of 3-T tagged and late enhancement MRI

ObjectiveTo determine LV function at different distances from myocardial infarction (MI) by using 3-T tagged MRI and late gadolinium enhancement (LGE).MethodsCardiac MR images were acquired from 21 patients with previous MI. The harmonic phase (HARP) method was used to calculate radial and circumferential strain (RS, CS). The two strains were synchronised by subtracting the CS from the RS at the same time, and this was defined as the efficient strain (ES). Peak strain (P-RS, P-CS, P-ES) and time to peak strain (T-RS, T-CS, T-ES) were used as estimates of contractile function. Based on the presence of LGE, myocardium was classified into infarct, border zone, adjacent and remote areas.ResultsP-RS and P-ES were significantly greater for remote than for adjacent and infarct areas. P-CS values were significantly greater for remote and border zone than for infarct areas. T-RS and T-ES were significantly shorter for remote and border zone than for infarct areas. T-CS was significantly shorter for border zone than for infarct areas.ConclusionContractile dysfunction demonstrated by peak strain was correlated with location at different distances from the infarct. In the border zone, contractile deformation was characterised as earlier T-RS, T-CS and T-ES and greater P-CS than in the infarct area.

Evaluation of the number of SPECT projections in the ordered subsets-expectation maximization image reconstruction method

Filtered back projection (FBP) method, maximum likelihood-expectation maximization (ML-EM) method, and ordered subsets-expectation maximization (OS-EM) method are currently used for reconstruction of SPECT images in clinical studies. In the ML-EM method, images of good quality can be reconstructed even with a small sampling number of projection data, when compared with FBP. Shorter acquisition time and less radionuclide dose are preferable in the clinical setting if image quality is the same. In this study, we attempted to find optimal conditions for reconstruction of OS-EM images with commonly used sampling numbers of 30, 60 and 120 (step angles: 12°, 6°, and 3°, respectively), with acquisition counts/projection of 30, 60, 120 and 240 each. We adjusted the pixel counts of reconstructed images to be constant, by setting combination of sampling number and counts/projection (120 sampling number for 30 counts/projection, 60 for 60, and 30 for 120). Among the 3 acquisition conditions, the small sampling number of 30 had large acquisition counts per direction, resulting in low signal to noise ratio. Under this condition, the resolution was slightly low, but the uniformity of images was high. The combination of OS-EM and smaller sampling projection number may be clinically useful with reduction of the examination time, which is also beneficial to reduce dead time for gamma-camera rotation.

Validity of microsphere model in cerebral blood flow measurement using N-isopropyl-p-(I-123) iodoamphetamine

A microsphere model is sometimes used when calculating cerebral blood flow (CBF) using N-isopropyl-p-[I-123]iodoamphetamine (IMP), and is based on the assumption that there is essentially no washout of IMP. The validity of a microsphere model was investigated by comparison with the values of CBF obtained by means of a model which takes into consideration the diffusion of IMP from brain tissue to blood (nonmicrosphere model). When calculating CBF by the latter model, the look-up table method was used with expression of the double integral in the model equation by the recursion relations, a method which is useful for obtaining pixel-by-pixel values. The average rate constants for diffusion from brain to blood of gray and white matter were 0.021 and 0.0016 min-1, respectively. The values of CBF obtained by applying a microsphere model to the data acquired from 0 to 3.2 min after IMP injection were overestimated by approximately 23% compared with those values obtained using a nonmicrosphere model. This is considered to be due to the effect of the IMP activity in the vascular space. Values obtained using the data acquired from 3.2 to 6.4 min were underestimated by approximately 15%. When the values of CBF obtained by a microsphere model were interpolated, they became nearly equal to those obtained using a nonmicrosphere model at about 4 to 5 min after injection. This is suggested to be the reason why the underestimation due to diffusion from brain to blood is cancelled out by the overestimation due to the IMP in the vascular space. Our preliminary results suggest that it is necessary to take the diffusion of IMP from brain tissue to blood into account for the quantification of CBF using IMP.

LAD Stenosis Detected by Subsecond Spiral CT

A50-year-old man with angina pectoris was hospitalized for coronary angiography. He was diagnosed with angina pectoris from the typical symptom (angina on exercise), positive exercise ECG (depressed ST-T in leads I, aVL, and V1 through V3), and positive exercise 201Tl single photon emission CT (decreased 201Tl perfusion in anteroseptal wall on exercise and significant redistribution on the 4-hour delayed …

Myocardial ischemia in acute coronary syndrome: assessment using 64-MDCT.

OBJECTIVE We investigated the performance of 64-MDCT myocardial imaging in assessing myocardial ischemia in acute coronary syndrome (ACS). MATERIALS AND METHODS Cardiac CT was performed in 35 patients with ACS: 24 patients with acute myocardial infarction (AMI) and 11 patients with unstable angina pectoris (UAP). We reconstructed 2D myocardial images at diastolic and systolic phases using the same raw data as those used for coronary CT angiography. The CT number in the myocardium was used as an estimate of ischemia. The myocardium was shown using a color scale that depicts faint low-density areas more clearly than gray scale. We evaluated the variations in myocardial enhancement during the cardiac cycle in the territory of the culprit lesion. In addition, we classified patients on the basis of the transmurality of myocardial enhancement and examined whether this feature correlates with myocardial damage. RESULTS Myocardial imaging at systole showed myocardial hypoenhancement in territories of the culprit lesion in 91% of patients with ACS, 96% of patients with AMI, and 75% of patients with UAP. The hypoenhancement areas at systole tended to be more extensive than those at diastole. The transmural extent of hypoenhancement at systole correlated with myocardial damage, which was shown by myocardial biomarkers. CONCLUSION CT myocardial imaging can be used to assess myocardial ischemia in the appropriate region of ACS with high sensitivity.