Elsevier

Magnetic Resonance Imaging

Volume 20, Issue 9, November 2002, Pages 643-648
Magnetic Resonance Imaging

Detectability of blood oxygenation level-dependent signal changes during short breath hold duration

https://doi.org/10.1016/S0730-725X(02)00595-7Get rights and content

Abstract

Blood oxygenation level-dependent (BOLD) signal increases induced by hypercapnia stress has been recently investigated in human brains, which may be clinically relevant because it reflects cerebral hemodynamic response to vasodilatation. The aims of this study were to investigate the detectability of BOLD signal changes due to short breath holding and the feasibility of this technique in routine clinical practice. The results showed that significant BOLD responses could be detected in the gray matter for a breath hold duration as short as 10 s. Breath hold duration correlated strongly with the full width at half maximum of the hemodynamic response (r2 = 0.975, p < 0.02), but not with the maximum signal change or the onset time. The fraction activation volume increased as the breath hold duration lengthened, reaching a plateau approximately at 20 s. Considering breath-holding capability of patients and detectability of BOLD signal changes, breath holding with a 20-s duration is suggested to be applied for clinical applications.

Introduction

With the progress of functional MRI (fMRI), techniques for detecting cerebral hemodynamic response have experienced tremendous advances in the last decade. One of the most commonly used techniques is blood oxygenation level-dependent (BOLD) contrast imaging that utilizes paramagnetic deoxyhemoglobin as an endogenous contrast agent [1], [2], [3]. During functional brain activity, the relative change of cerebral metabolic rate of oxygen (CMRO2) was found to be much less than that of cerebral blood flow (CBF) [4], [5], [6], [7], leading to an increase of the BOLD signal. Under the assumption that oxygen consumption rate remains invariant, substances that can evoke cerebral vasodilatation with resultant CBF increases are supposed to contribute to changes in BOLD signals.

In human, 5% and 7% CO2 inhalation raises CBF by approximately 50% and 100%, respectively [8]. Besides CO2 inhalation, hypercapnia stress can be easily achieved by simple breath holding. Stillman et al. and Moritz et al. reported a 3-10% BOLD signal increase in normal adults due to breath holding [9], [10]. Kastrup et al. investigated CBF changes with BOLD imaging in different breath hold durations (40 s, 30 s, and 18 s) [11]. They demonstrated that the BOLD signal increases of the activated pixels varied from 0.8% to 3.5%, depending on the breath hold duration and techniques. Recently, Kastrup et al. investigated the regional variation of BOLD signal changes during 30-s breath holding [12]. They found the highest response was in cerebellum and visual cortex, whereas the lowest response in frontal cortex. In general, all the studies found that the BOLD signal changes in gray matter were far greater than that in white matter. Besides normal adults, Robinson et al. investigated the tumor blood flow changes in rats during carbogen (95% O2, 5% CO2) inhalation using BOLD imaging technique [13]. They showed that the image intensity of tumor increased up to 100% during inhalation of carbogen. In addition to animal studies, Griffiths et al. monitored responses of tumors during carbogen breathing in 31 patients with primary and metastatic diseases using BOLD technique [14]. They reported 17 out of 34 tumors showed enhanced image intensity, and concluded that the responses of human tumors to carbogen breathing were heterogeneous.

Most recently, Kastrup et al. compared the cerebrovascular reactivity between CO2 inhalation and breath holding with BOLD imaging, and found that there was a good correlation between BOLD intensity changes during breath holding and CO2 inhalation [15]. This suggested the possibility to include a simple breath holding test instead of CO2 inhalation into regular clinical examination. However, in clinical settings, patients may not be able to hold their breath for a period that is long enough to cause a significant increase in BOLD signal. Recently, both CBF and BOLD responses due to brief brain stimulation have been investigated in depth [16], [17], [18]. However, to date, the behavior of BOLD signal changes during short breath hold duration is not fully understood. Therefore, to increase the feasibility of the use of breath holding test in clinical functional neuroimaging, it is necessary to determine the minimal breath hold duration during which reliable BOLD signal changes can be detected.

In this report, the detectability of BOLD responses during short breath hold duration was assessed in six normal subjects by examining the percent signal change and the fraction activation volume. In addition, correlations between breath hold duration and BOLD response parameters, such as onset time, full width at half maximum (FWHM), and maximum signal change, were also determined. Based on the present study, we revealed the possibility for future application of BOLD imaging with a simple breath holding test in routine clinical examination.

Section snippets

Subjects

Experiments were performed on a 1.5-T Magnetom Vision MRI scanner (Siemens, Erlangen, Germany) at the Chang Gang Memorial Hospital. Six normal human volunteers (four men, two women, age range = 20-30 years) participated in this study. Informed consent was obtained from all the subjects after the nature of the study was explained. Prior to fMR imaging, each subject was instructed the entire experimental procedures and exercised the task designs to reduce anxiety and enhance the task performance.

Results

Fig. 1(a) to (f) show the averaged BOLD signal time courses over the six subjects in different breath-holding conditions with duration of 3 s, 5 s, 10 s, 15 s, 20 s and 30 s, respectively. There is no significant signal change pattern in 3-s and 5-s breath-holding studies (Fig. 1(a), (b)). In 10-s, 15-s, 20-s and 30-s breath-holding studies, BOLD signal changes in gray matter clearly follow the breath holding periods in all the five experimental cycles (Fig. 1(c)-(f)). Furthermore, the BOLD

Discussion

One of the major findings in this study was that significant BOLD responses could be detected in the gray matter for a breath hold duration as short as 10 s. This suggests the feasibility of including a simple breath holding test in routine clinical neuroimaging examination. The present study demonstrated that a simple breath holding test can evoke hypercapnia stress and causes BOLD signal increases, similar with the changes induced by CO2 inhalation. And, furthermore, the BOLD image data

Acknowledgements

We thank Dr. Jia-Hong Gao for his insightful comments and discussion. This work was supported by National Science Council of Taiwan (NSC90-2314-B-182-094) and Chang Gung Memorial Hospital Research Grant (CMRP1065).

References (21)

There are more references available in the full text version of this article.

Cited by (0)

View full text