Optimizing contrast enhancement during helical CT of the liver: a comparison of two bolus tracking techniques.

Abstract

OBJECTIVE. The purposeof this studywas to evaluatea recentlydevelopedhardware and software system for CT scanning that generates images in real time and switches to heli cal CT scanning by either a visual cue or a region of interest (ROI) amplitude threshold. SUBJECTS AND METHODS. We randomlyandprospectivelydivided 120 abdominalCT examinations into three groups. Two groups received 75 ml of contrast agent at 1.5 ml/sec.Helical CT scanning began after visualization of the contrast bolus arrival in the hepatic veins (visual cue triggering) (39 patients) or after reaching an ROI threshold (automated ROI threshold triggering) (39 patients). A third group served as a control group (42 patients) and received 150 ml of contrast agent at I mllsec. Quality of hepatic enhancement was assessed objectively and subjectively. Comparisons were made after stratifying each group into three weight classes. RESULTS. Errorsoccurredin 12 (31%) of 39 examinationsin the groupwith automatedROl threshold triggering. In that group, we found a significantly (p < .04) lower mean hepatic enhancement in two of three weight categories, and a significantly (p < .04) lower mean sub jective scan quality in one of three weight categories, than we found in the group with visual cue triggering. CONCLUSION.Optimizing portalvenousphasehelicalCT of the liver after a low-vol ume bolus of contrast agent and an injection rate of 1.5 mI/sec is best achieved by initiating helical CT scanning after visualizing the contrast bolus arrival within the liver rather than af ter reaching a preset attenuation threshold.T he use of helical CT, with its abil ity to image a target organ rap idly, can greatly improve the probability of seeing all desired anatomy in a short time [1â€"5]. However, the rapid scan ning time of helical CT can increase the diffi culty of optimizing the delay time between the beginning of contrast material injection and the acquisition of images [2â€"4].Recent advances in reconstructionspeed al low helical CT scanning delay time to be individualizedon a case-by-case basis by mon itoring contrast enhancement with rapidly re constructed CT images obtained at a stationary level within or near the organ of interestduring the bolus injection of IV contrast material. Sil verman et al. [6][7][8] and Kopka et al. [9,10] evaluated a system in which this rapid recon struction process allowed monitoring of hepatic contrast enhancement by near real-time graphic and numeric display ofhepatic density in a pre determined region of interest (ROl). Their sys tem allowed the operator to initiate helical CT imaging when hepatic density reached a preset numeric threshold (automated ROI threshold triggering). These investigators reported an im provement in the quality of hepatic contrast en hancement when compared with that of standard helical examinations using a fixed scanning delay time and suggested that the amount of contrast material could be reduced without compromising scan quality [8, 10].A recently developed hardware and soft ware system devised for bol...

Automatic bolus tracking in monophasic spiral CT of the liver: liver-to-lesion conspicuity

“…A few reports have shown that automatic bolus tracking is a suitable method for optimizing the contrast enhancement of the liver [15,21,22,23]. Studies comparing this technique with time-delay scanning showed significantly higher mean parenchymal enhancement using bolus tracking [15,21,23].…”

“…They found that failures were more frequent especially in patients who are heavy and inpatients. Schweiger et al [22] even observed that hepatic scanning by visualizing the contrast bolus arrival would be better than by reaching a preset attenuation threshold; they, however, used an injection rate of only 1.5 ml/s. In the study by Dinkel et al [21] 1 of 39 patients did not reach the enhancement threshold of 31 HU.…”

CT fluoroscopic guidance for percutaneous needle placement into abdominopelvic lesions with difficult access routes

“…With our imaging parameters, 120 kVp and 50 mA, the estimated absorbed skin and bone marrow doses to the patient are 396 and 120 mrad (3.96 and 1.20 mGy) for each second of exposure [4,15]. Although CTF time was relatively high for our patients compared with general abdominal intervention using CTF guidance at other institutions [5][6], it is likely a reflection of a combination of factors including the use of continuous CTF for lesion localization with and without abdominal wall compression, our lack of a compression device through which biopsies can be performed, and the difficult nature of cases described herein.…”

Bolus chasing computed tomography angiography using local maximum tracking method

“…Accurately estimating the bolus arrival time and activating the control is a critical part of CTA (Hittmair, 2001;Paulson, 1998;Schweiger, 1998). In particular, the traditional constant speed control is extremely sensitive with respect to the activating time.…”