Takashi Ichihara

Quantitative analysis of first-pass contrast-enhanced myocardial perfusion MRI using a Patlak plot method and blood saturation correction.

The objectives of this study were to develop a method for quantifying myocardial K1 and blood flow (MBF) with minimal operator interaction by using a Patlak plot method and to compare the MBF obtained by perfusion MRI with that from coronary sinus blood flow in the resting state. A method that can correct for the nonlinearity of the blood time–signal intensity curve on perfusion MR images was developed. Myocardial perfusion MR images were acquired with a saturation‐recovery balanced turbo field‐echo sequence in 10 patients. Coronary sinus blood flow was determined by phase‐contrast cine MRI, and the average MBF was calculated as coronary sinus blood flow divided by left ventricular (LV) mass obtained by cine MRI. Patlak plot analysis was performed using the saturation‐corrected blood time–signal intensity curve as an input function and the regional myocardial time–signal intensity curve as an output function. The mean MBF obtained by perfusion MRI was 86 ± 25 ml/min/100 g, showing good agreement with MBF calculated from coronary sinus blood flow (89 ± 30 ml/min/100 g, r = 0.74). The mean coefficient of variation for measuring regional MBF in 16 LV myocardial segments was 0.11. The current method using Patlak plot permits quantification of MBF with operator interaction limited to tracing the LV wall contours, registration, and time delays. Magn Reson Med, 2009.

Serial change of iodine-123 metaiodobenzylguanidine (MIBG) myocardial concentration in patients with dilated cardiomyopathy

Serial change of the metaiodobenzylguanidine iodine-123 (123I-MIBG) myocardial concentration was investigated in patients with dilated cardiomyopathy (DCM). Eight DCM patients and 6 control subjects were examined. After the injection of thallium-201 and 123I-MIBG, planar chest images were obtained simultaneously for both tracers in every 30–60 min over 5 h. Serial changes of myocardial uptake ratio (MUR) were compared for both tracers. In DCM, the initial MUR of 123I-MIBG did not differ significantly from that of the controls. The washout of 123I-MIBG from the myocardium, however, was significantly increased in DCM. In particular, the decrease in the early phase (15–45 min) was significantly larger in DCM than in the controls (21.2%±7.5% vs. 5.3%±4.0%, P <0.01), showing a significant negative correlation with the left ventricular ejection fraction (r = −0.72 P < 0.05). For 201TI, neither the initial MUR nor the washout rate different significantly between the two. Thus, an early rapid decrease of the 123I-MIBG myocardial concentration might characterize DCM and reflect the severity of this disease.

Quantification of myocardial blood flow using model based analysis of first-pass perfusion MRI: extraction fraction of Gd-DTPA varies with myocardial blood flow in human myocardium.

For the absolute quantification of myocardial blood flow (MBF), Patlak plot‐derived K1 need to be converted to MBF by using the relation between the extraction fraction of gadolinium contrast agent and MBF. This study was conducted to determine the relation between extraction fraction of Gd‐DTPA and MBF in human heart at rest and during stress. Thirty‐four patients (19 men, mean age of 66.5 ± 11.0 years) with normal coronary arteries and no myocardial infarction were retrospectively evaluated. First‐pass myocardial perfusion MRI during adenosine triphosphate stress and at rest was performed using a dual bolus approach to correct for saturation of the blood signal. Myocardial K1 was quantified by Patlak plot method. Mean MBF was determined from coronary sinus flow measured by phase contrast cine MRI and left ventricle mass measured by cine MRI. The extraction fraction of Gd‐DTPA was calculated as the K1 divided by the mean MBF. The extraction fraction of Gd‐DTPA was 0.46 ± 0.22 at rest and 0.32 ± 0.13 during stress (P < 0.001). The relationship between extraction fraction (E) and MBF in human myocardium can be approximated as E = 1 − exp(−(0.14 × MBF + 0.56)/MBF). The current results indicate that MBF can be accurately quantified by Patlak plot method of first‐pass myocardial perfusion MRI by performing a correction of extraction fraction. Magn Reson Med, 2011.

A Method for Reconstructing the Arterial Input Function during Helical CT: Implications for Myocardial Perfusion Distribution Imaging

PURPOSE To determine if a multidetector computed tomographic (CT) image acquisition and analysis method can enable accurate measurement of the arterial input function (AIF) during first-pass adenosine stress helical multidetector CT angiography and to test the effect of using this method on the semiquantitative assessment of myocardial perfusion distribution. MATERIALS AND METHODS The animal care and use committee of Johns Hopkins University approved the use of all procedures. The AIF was reconstructed by using a combination of bolus-tracking and time-registered helical multidetector CT data. After the AIF reconstruction method was validated in healthy animals, coronary stenosis was induced in seven dogs and contrast material-enhanced multidetector CT was performed during adenosine infusion (0.14-0.21 mg per kilogram of body weight per minute). Myocardial attenuation density (AD) parameters normalized to portions of the AIF were compared with microsphere myocardial blood flow (MBF) measurements at linear regression analysis. RESULTS There was no significant difference between the area under the curve (AUC) for dynamic multidetector CT-derived AIF (3108 + or - 1250 [standard deviation]) and that for combined bolus-tracking and time-registered multidetector helical CT-derived AIF (3086 + or - 941) (P = .90). When AIF analysis was applied to helical multidetector CT myocardial perfusion measurements, the correlation between MBF and mean myocardial AD normalized to the AUC for the entire AIF was significant (R(2) = 0.82, P <.001). Myocardial AD normalized to the AUC for the AIF measured during helical multidetector CT correlated best with MBF (R(2) = 0.86, P <.001). CONCLUSION The combination of bolus tracking and time-registered helical imaging enables reconstruction of the AIF during multidetector CT perfusion imaging. The helical CT AIF can be used to improve the semiquantitative assessment of myocardial perfusion distribution.

Robot‐assisted partial nephrectomy: Superiority over laparoscopic partial nephrectomy

Nephron‐sparing surgery has been proven to positively impact the postoperative quality of life for the treatment of small renal tumors, possibly leading to functional improvements. Laparoscopic partial nephrectomy is still one of the most demanding procedures in urological surgery. Laparoscopic partial nephrectomy sometimes results in extended warm ischemic time and severe complications, such as open conversion, postoperative hemorrhage and urine leakage. Robot‐assisted partial nephrectomy exploits the advantages offered by the da Vinci Surgical System to laparoscopic partial nephrectomy, equipped with 3‐D vision and a better degree in the freedom of surgical instruments. The introduction of the da Vinci Surgical System made nephron‐sparing surgery, specifically robot‐assisted partial nephrectomy, safe with promising results, leading to the shortening of warm ischemic time and a reduction in perioperative complications. Even for complex and challenging tumors, robotic assistance is expected to provide the benefit of minimally‐invasive surgery with safe and satisfactory renal function. Warm ischemic time is the modifiable factor during robot‐assisted partial nephrectomy to affect postoperative kidney function. We analyzed the predictive factors for extended warm ischemic time from our robot‐assisted partial nephrectomy series. The surface area of the tumor attached to the kidney parenchyma was shown to significantly affect the extended warm ischemic time during robot‐assisted partial nephrectomy. In cases with tumor‐attached surface area more than 15 cm2, we should consider switching robot‐assisted partial nephrectomy to open partial nephrectomy under cold ischemia if it is imperative. In Japan, a nationwide prospective study has been carried out to show the superiority of robot‐assisted partial nephrectomy to laparoscopic partial nephrectomy in improving warm ischemic time and complications. By facilitating robotic technology, robot‐assisted partial nephrectomy will be more frequently carried out as a safe, effective and minimally‐invasive nephron‐sparing surgery procedure.

Quantitative Analysis of First-Pass Contrast-Enhanced Myocardial Perfusion Multidetector CT Using a Patlak Plot Method and Extraction Fraction Correction During Adenosine Stress

The purpose of this study was to develop a quantitative method for myocardial blood flow (MBF) measurement that can be used to derive accurate myocardial perfusion measurements from dynamic multidetector computed tomography (MDCT) images by using a compartment model for calculating the first-order transfer constant (K1) with correction for the capillary transit extraction fraction (E). Six canine models of left anterior descending (LAD) artery stenosis were prepared and underwent first-pass contrast-enhanced MDCT perfusion imaging during adenosine infusion (0.14-0.21 mg/kg/min). K1, which is the first-order transfer constant from left ventricular (LV) blood to myocardium, was measured using the Patlak plot method applied to time-density curve data of the LV blood pool and myocardium. The results were compared against microsphere MBF measurements, and the extraction fraction of contrast agent was calculated. K1 is related to the regional MBF as K1=EF, E=(1-exp(-PS/F)), where PS is the permeability-surface area product and F is myocardial flow. Based on the above relationship, a look-up table from K1 to MBF can be generated and Patlak plot-derived K1 values can be converted to the calculated MBF. The calculated MBF and microsphere MBF showed a strong linear association. The extraction fraction in dogs as a function of flow (F) was E=(1- exp(-(0.253F+0.7871)/F)). Regional MBF can be measured accurately using the Patlak plot method based on a compartment model and look-up table with extraction fraction correction from K1 to MBF.

Quantitative analysis of first-pass contrast-enhanced myocardial perfusion multidetector CT using a Patlak plot method and extraction fraction correction during adenosine stress

The purpose of this study was to develop a quantitative method for myocardial blood flow (MBF) measurement that can be used to derive accurate myocardial perfusion measurements from dynamic multidetector computed tomography (MDCT) images by using a compartment model for calculating the first-order transfer constant (<i>K</i>₁) with correction for the capillary transit extraction fraction (<i>E</i>). Six canine models of left anterior descending (LAD) artery stenosis were prepared and underwent first-pass contrast-enhanced MDCT perfusion imaging during adenosine infusion (0.14-0.21 mg/kg/min). <i>K</i>₁ , which is the first-order transfer constant from left ventricular (LV) blood to myocardium, was measured using the Patlak plot method applied to time-attenuation curve data of the LV blood pool and myocardium. The results were compared against microsphere MBF measurements, and the extraction fraction of contrast agent was calculated. <i>K</i>₁ is related to the regional MBF as <i>K</i>₁=<i>EF</i>, <i>E</i>=(1-<i>exp</i>(-<i>PS</i>/<i>F</i>)), where <i>PS</i> is the permeability-surface area product and <i>F</i> is myocardial flow. Based on the above relationship, a look-up table from <i>K</i>₁ to MBF can be generated and Patlak plot-derived <i>K</i>₁ values can be converted to the calculated MBF. The calculated MBF and microsphere MBF showed a strong linear association. The extraction fraction in dogs as a function of flow (<i>F</i>) was <i>E</i>=(1-<i>exp</i>(-(0.2532<i>F</i>+0.7871)/<i>F</i>)) . Regional MBF can be measured accurately using the Patlak plot method based on a compartment model and look-up table with extraction fraction correction from <i>K</i>₁ to MBF.

Linear quantification correction for myocardial perfusion imaging from x-ray coronary angiography

Myocardial perfusion imaging from x-ray coronary angiography is important with clinical benefits because online real-time assessment of myocardial blood flow can promote the clinical outcomes of interventional treatments for coronary artery disease. In this paper, we aim at the nonlinearity problem of contrast image measurements for the perfusion estimation, since x-ray nonlinear responses of iodinated contrast agent is always an important concern when lacking of x-ray depth information on 2D angiography. A new approach is developed to perform linear quantification correction to angiographic measurements in terms of iodine concentration for estimated body thickness. We recognize the causes of nonlinear measurements from three different sources, that is, image processing artifacts of background subtraction, x-ray physics causes of beam hardening, photon scattering and detector glare if image intensifier applied, as well as clinical application issue of residual contrast agents in myocardium during cardiac catheterization heart procedure. Correspondingly, the developed approach involves three countermeasures to handle the three nonlinear sources. In order to compensate the registration artifacts of background subtraction, the technique of layer image processing is applied to compensate the different cardiac and breathing motions. A prior phantom-based calibration is implemented to make a lookup table of correction models. A polynomial model selected from the table is used online to correct the nonlinear measurements due to x-ray physics causes. For the effect of residual contrast agent, a new workflow of triple background subtractions is proposed by introducing an initial background image. Finally, the proposed approach is validated with pre-clinical studies of porcine models.

Evaluation of equivalence of upslope method-derived myocardial perfusion index and transfer constant based on two-compartment tracer kinetic model

The purpose of this study was to describe the upslope method-derived myocardial perfusion index using the parameters based on a tracer kinetic model of iodixanol contrast agent and to validate this theoretically derived relationship using an ischemic canine model. The established modified Kety model was used to describe the extravascular diffusion of iodixanol contrast agent, which undergoes no cellular uptake or metabolism. This model consists of two functional compartments, one describing the vascular compartment and the second representing all myocardial capillaries, interstitium, and cells. These compartments are connected by two rate constants, K1 and k2, which represent the first-order transfer constants from the left ventricular (LV) blood to myocardium and from myocardium to the vascular system, respectively. In the early phase after the arrival of contrast agent in the myocardium, the relationship between K1 and the concentrations of iodixanol contrast agent in the myocardium and arterial blood (LV blood) is described by K1 = {dCmyo(tpeak)/dt}/Ca(tpeak) (Eq. 1), where Cmyo(t) is the relative concentration of iodixanol contrast agent in the myocardium at time t, Ca(t) is the relative concentration of iodixanol contrast agent in the LV blood, and tpeak is the time at the peak of Ca(t) and maximum upslope of Cmyo(t). Six canine models of left anterior descending (LAD) artery stenosis were prepared and underwent first-pass contrast-enhanced mult-detector row computed tomography (MDCT) perfusion imaging during adenosine infusion (0.14–0.21 mg/kg/min) to study a wide range of flow rates. K1 was measured using the Patlak plot method and upslope method applied to time-attenuation curve data of the LV blood pool and myocardium. The results were compared against microsphere myocardial blood flow measurements. The Patlak plot-derived K1 and upslope method-derived K1 showed a good linear association. Regional K1 can be measured accurately using the upslope method-derived myocardial perfusion index based on a compartment model.

Quantitative assessment of regional systolic and diastolic functions and temporal heterogeneity of myocardial contraction in patients with myocardial infarction using cine magnetic resonance imaging and Fourier fitting

PURPOSE The objective of this study is to determine regional left ventricle (LV) function and temporal heterogeneity of LV wall contraction by analyzing regional time-volume curve (TVC) after Fourier fitting and to assess altered systolic and diastolic functions and temporal indices of myocardial contraction in infarcted segments in comparison with noninfarcted myocardium in patients with myocardial infarction (MI). METHODS Steady-state cine magnetic resonance (MR) and late gadolinium-enhanced (LGE) MR images were acquired using a 1.5-T MR system in 60 patients with MI. Regional LV function was determined by analyzing regional TVC in 16 segments. The fitted regional TVC was generated by Fourier curve fitting with five harmonics. Regional LV ejection fraction (EF), peak ejection rate (PER), peak filling rate (PFR), time to end-systole and time to peak filling (TPF) were determined from TVC and the first derivative curve. RESULTS On LGE MR imaging (MRI), MI was observed in 307 of 960 segments (32.0%). Regional EF and PER averaged in LGE segments were 49.3+/-14.5% and 2.83+/-0.65 end-diastolic volume (EDV)/s, significantly lower than those in normal segments (66.7+/-11.9% and 3.63+/-0.60 EDV/s, P<.001 and P<.01, respectively). In addition, regional PFR, an index of diastolic function, was significantly reduced in LGE segments (1.94+/-0.54 vs. 2.86+/-0.68 EDV/s, P<.01). Time to end-systole and TPF were significantly greater in LGE segments (380.2+/-57.6 and 169.3+/-45.4 ms) than in normal segments (300.9+/-55.1 and 132.3+/-43.0 ms, P<.01 and P<.01, respectively). CONCLUSIONS Analysis of regional TVC on cine MRI after Fourier fitting allows quantitative assessment of regional systolic and diastolic LV functions and temporal heterogeneity of LV wall contraction in patients with MI.