JP6473882B1 - How to determine the shooting time - Google Patents

Abstract

By calculating a moving speed of a contrast medium in an aorta, it is possible to perform an aortic contrast CT with a minimum necessary contrast medium.
Timing bolus imaging is performed at the level of the base of the ascending aorta, and two time density curves are drawn for the ascending aorta and the descending aorta. The moving speed of the contrast medium in the aorta is calculated from the difference in peak time, and the time taken for actual imaging is determined. With this method, aortic contrast CT can be imaged with the minimum necessary contrast medium.
[Selection] Figure 2

Description

The present invention is a technique for imaging with a minimum necessary contrast agent when imaging an aortic contrast CT.

In the diagnosis of aortic aneurysm and dissection, aortic CT is the most commonly used diagnostic method. Since the imaging range is wide from the chest to the pelvis, it has been the usual practice to inject a 70-100 mL contrast medium over about 20 seconds.

However, since the contrast agent is excreted from the kidney to the outside of the body, when the amount of contrast agent used increases, it causes so-called contrast nephropathy that causes a decrease in renal function. Many patients with aortic disease often have impaired renal function. Therefore, if the amount of contrast medium used in the test can be reduced, the risk of contrast medium nephropathy will be reduced.

The reason why the amount of contrast medium used in conventional imaging could not be reduced is based on the idea that imaging is performed in a state where the entire aorta is uniformly filled with the contrast medium. However, since actual CT imaging uses a detector of about 4 cm to take a spiral from the chest to the pelvis, an image of the aorta contrasted if only the part being imaged is filled with contrast medium Can be created. However, the blood flow in the aorta varies from patient to patient. Therefore, if a method for measuring the time at which the contrast medium arrives at the aorta and the speed at which it passes through the aorta is established, CT imaging can be performed with a minimum of contrast medium.

A method called a timing bolus method is generally used as a method for estimating the time at which a contrast medium arrives at the aorta after the contrast medium is injected. In this method, a small amount of contrast medium (approximately 10 mL) is injected, the aorta is continuously photographed at 1-second intervals, and the time when the contrast medium reaches its peak is estimated (Figure 1). In the past, only one time concentration curve was measured and only the time to reach the peak was recorded (Fig. 1).

In the present invention, timing bolus imaging is performed at the height of the base of the ascending aorta, and two time density curves of the ascending aorta and the descending aorta are measured (FIG. 2). Record the difference in peak time for each time concentration curve (T1). Next, the length of the thoracic aorta (L0 × 2), the imaging range length of the chest (L1), and the imaging range length of the abdomen (L2) are also recorded. Using these values, the time taken for photographing is calculated by the following formula. However, since the current measurement method cannot accurately measure blood flow in the abdominal aorta, the imaging time is determined using the following method. First, since the flow velocity is lower in the abdominal aorta than in the thoracic aorta, the speed is 60%. Furthermore, when there is an abdominal aortic aneurysm or after stent treatment, a predetermined time (C) is added. Based on these assumptions, the final shooting time is determined. However, if the blood flow is very fast (when the shooting time is calculated short) and slow (when the shooting time is calculated long), this estimation formula empirically deviates from the actual situation, so the lower limit of the shooting time Shoot for 10 seconds and the upper limit is 20 seconds.

In actual imaging, approximately 40 mL of contrast medium is injected for 9 seconds, and imaging is started from the time when the descending aorta reaches its peak in timing bolus imaging, and imaging is performed at the imaging time (T) calculated above. By using this method, it is possible to reduce the amount of contrast medium used by half or less compared to conventional imaging methods.

Bae KT. Intravenous Contrast Medium Administration and Scan Timing at CT: Considerations and Approaches. Radiology 2010; 256 (1): 32-61.

The problem to be solved is to reduce the amount of contrast agent used in aortic contrast CT to the minimum necessary.

In the present invention, since the peak of the contrast medium in the aorta can be tracked and imaged, the contrast medium required for imaging can be minimized.

In the present invention, it is not necessary to fill the entire aorta with the contrast medium, and only the site being imaged needs to be imaged. Therefore, the contrast medium required for imaging may be about 40 mL, which is less than half of the conventional usage. It becomes.

It is a figure explaining the conventional timing bolus method. It is the figure explaining the method for calculating the moving speed of the contrast agent in an aorta for every patient. It is the figure which showed the three-dimensional image of the aorta image | photographed with the 40 mL contrast agent using the method in this invention.

The moving speed of the contrast agent was calculated by drawing two time density curves using the timing bolus method.

FIG. 2 shows a process of determining the time taken for imaging the aorta using the method of the present invention.

The peak difference (T1) between the ascending aorta and descending aorta is 3 seconds. Since the thoracic aorta length (L0 × 2) is 140 mm, the thoracic aorta may be imaged at 47 mm / s (V1). Therefore, the speed (V2) for imaging the abdominal aorta is 28 mm / s. Since the chest imaging length (L1) is 125 mm, the abdominal imaging length (L2) is 435 mm, and there is a 45 mm abdominal aortic aneurysm, the imaging time (T) is calculated as 2.7 + 15.5 + 1 = 19.2 seconds.

FIG. 3 is a three-dimensional image of the aorta when the aorta is imaged with 40 mL of contrast medium over a period of 19.2 seconds calculated by the method of the present invention.

Since the amount of contrast medium used in aortic contrast CT can be reduced to less than half of the conventional level, the risk of causing complications of contrast medium nephropathy due to contrast CT can be reduced. In addition, aortic contrast CT can be performed even in patients with impaired renal function, so the indication of this test is expanded.

1 descending aorta
2 Ascending aorta

Claims (4)

A method for determining imaging time in aorta CT imaging,
Creating a time-concentration curve of the ascending aorta and descending aorta from images obtained by continuously photographing a cross section passing through the base of the ascending aorta;
Obtaining the time difference between the peak time of the time density curve of the ascending aorta and the peak time of the time density curve of the descending aorta, and the length of the thoracic aorta;
Calculating a thoracic aorta contrast agent moving speed based on the time difference and the length of the thoracic aorta;
Obtaining an imaging range length of the chest, and calculating an imaging time of the chest based on the imaging range length of the chest and the thoracic aorta contrast medium moving speed;
A method for determining a shooting time. Calculating an abdominal aorta contrast agent moving speed that is slower than the thoracic aorta contrast agent moving speed based on the thoracic aorta contrast agent moving speed and a predetermined coefficient;
The method includes: obtaining an abdominal imaging range length, and calculating an abdominal imaging time based on the abdominal imaging range length and the abdominal aorta contrast medium moving speed. Decision method. Based on the imaging time of the chest and the imaging time of the abdomen, the step of calculating the imaging time from the start of imaging in aortic CT imaging,
The thoracic aorta contrast agent moving speed is calculated based on the following formula:
V1 = L0 / T1
The abdominal aorta contrast agent moving speed is calculated based on the following formula:
V2 = 0.6 × V1
The shooting time from the start of shooting is calculated based on the following formula:
T = (L1 / V1) + (L2 / V2) + C
V1 is the thoracic aorta contrast agent moving speed,
L0 is the length of the thoracic aorta,
T1 is the time difference,
V2 is the abdominal aorta contrast agent moving speed,
T is the shooting time from the start of shooting,
L1 is the imaging range length of the chest,
L2 is the imaging range length of the abdomen,
C is a correction value, which is 1 second when the diameter of the abdominal aorta is 40 to 49 mm, 2 seconds when the diameter of the abdominal aorta is 50 mm or more, and 1 second after the abdominal aortic stent treatment. The method of determining an imaging time according to claim 2, wherein the time is 0 second when none of the conditions is satisfied. When the calculated shooting time from the start of shooting is shorter than 10 seconds, the shooting time from the start of shooting is set to 10 seconds,
The method of determining a shooting time according to claim 3, wherein when the calculated shooting time from the start of shooting is longer than 20 seconds, the shooting time from the start of shooting is set to 20 seconds.