Impact of field strength and RF excitation on abdominal diffusion-weighted magnetic resonance imaging

Table 1 Imaging parameters in the three imaging systems used for the patient population

	1.5T MR	non-dpTX 3.0T MR	dpTX 3.0T MR
TR/TE, ms	5600/75	6000/76	6400/63
Sequence type	EPI-SE	EPI-SE	EPI-SE
FOV, mm × mm	380 × 308	380 × 308	380 × 308
Matrix	192 × 156	192 × 156	192 × 156
Slice thickness, mm	6	5	5
Interslice gap, mm	0	0	0
Spatial resolution, mm³	2.0 × 2.0 × 6.0	2.0 × 2.0 × 5.0	2.0 × 2.0 × 5.0
Number slices	32	33	35
b-values	50, 400, 800	50, 400, 800	50, 400, 800
Parallel imaging	GRAPPA 2	GRAPPA 2	GRAPPA 2
Acquisition time, min	4:30	5:06	4:46
Respiratory control	Free breathing	Free breathing	Free breathing
Fat suppression	SPAIR	SPAIR	SPAIR
Averages	4	4	3
Bandwidth, Hz/px	1736	1736	1736

MR: Magnetic resonance.

Table 2 Imaging parameters in the three imaging systems used for the volunteer population

	1.5T MR	non-dpTX 3.0TMR	dpTX 3.0TMR
TR/TE, ms	6300/79	6600/80	6000/68
Sequence type	EPI-SE
FOV, mm × mm	380 × 297
Matrix	192 × 150
Slice thickness, mm	6
Interslice gap, mm	0
Spatial resolution, mm³	2.0 × 2.0 × 6.0
Number slices	35
b-values	0, 50, 100, 200, 400, 800
Parallel imaging	GRAPPA 2
Acquisition time, min	7:02	7:22	6:54
Respiratory control	Free breathing
Fat suppression	SPAIR
Averages	4
Bandwidth, Hz/px	1628

MR: Magnetic resonance.

Table 3 Mean signal-to-noise ratio measurements for the patient and volunteer populations across all b-values in all eight anatomical distributions

		Liver (right lobe)			1Liver (left lobe)			1Liver (caudate lobe)			1Pancreas (head)			Left Kidney			Right Kidney			Spleen			Muscle
	b-values (s/mm²)	50	400	800	50	400	800	50	400	800	50	400	800	50	400	800	50	400	800	50	400	800	50	400	800
Patients	non-dpTX 3.0T	26.6	19.6	16.3	12.5	9.9	9.1	24.1	18.1	16.1	51.6	29.6	21.3	201.7	83.2	(42.4)	168.72	(77.1)	(42.7)	107.8	81.1	59.2	33.2	19.3	11.9
	dpTX 3.0T	42.52	33.7	23.3	52.1	42.6	27.1	27.32	21.02	12.5	70.4	58.0	33.1	169.0	138.2	65.1	150.52	127.6	60.0	118.5	105.7	78.3	60.5	53.1	30.3
	1.5T	38.12	(24.6)	17.3	(28.6)	(16.8)	(11.3)	24.2	15.2	11.2	40.8	22.6	(14.9)	118.9	55.7	28.8	113.3	52.4	26.9	101.9	72.7	52.3	32.1	20.3	(13.4)
Volunteers	non-dpTX 3.0T	17.0	9.4	7.6	6.6	5.3	4.8	11.6	6.9	6.3	30.0	14.0	10.2	112.2	44.72	(22.5)	74.0	29.6	16.1	74.7	48.3	33.6	(23.1)	12.3	8.4
	dpTX 3.0T	29.52	14.92	10.7	44.9	20.0	13.6	25.8	11.42	7.9	76.1	30.5	18.8	155.1	59.72	30.8	130.5	50.4	26.3	106.62	75.3	55.5	47.4	23.9	13.2
	1.5T	27.92	13.72	10.82	(20.0)	(8.7)	(7.1)	19.0	9.5	7.9	30.1	13.1	9.8	83.4	31.5	16.4	72.2	27.8	14.6	76.3	48.9	34.5	16.6	10.3	8.3

¹Fields correspond to peripheral anatomical regions, while the ¹fields categorize the central anatomical regions. The numbers which are bolded have statistically higher single-to noise ratio values than both of the other imaging systems at the given b-value and regions of interest. The numbers which have a symbol (²) have higher Single-to noise ratio (SNR) values than only the lowest SNR measurement at the given b-value and region of interest (ROI). Items which are parenthesized are values that have the second-highest SNR, but are still significantly higher than the lowest at the given b-value and ROI.

Table 4 Image quality: Median values and percent of diagnostic studies

Image quality	Median-Patients		Median-Volunteers		No loss in diagnostic value		Non-diagnostic/low diagnostic value
	Reader 1	Reader 2	Reader 1	Reader 2	Patients	Volunteers	Patients	Volunteers
non-dpTX 3.0T	1	1	1	1.5	26%	40%	74%	60%
dpTX 3.0T	3	3	3	3	98%	100%	2%	0%
1.5T	3	3	2.5	3	94%	100%	6%	0%

The left half of the table depicts mean values as rated by the two radiologists based on the 4-point ordinal scale in which “3” = good for interpretation without noticeable limitations, “2” = adequate for basic interpretation with minor limitations, “1” = poor for basic interpretation, “0” = non-diagnostic and not adequate for basic interpretation. The right half of the table illustrates the percentage of images deemed to have “No loss in diagnostic value” (scored as ≥ 2) vs“Non-diagnositc/Low Diagnostic Value” (scored as ≤ 1). Numbers in bold are statistically different from the other two numbers within the column.

Table 5 Ghosting artifact: Median values and percent of diagnostic studies

Ghosting	Median-Patients		Median-Volunteers		No loss in diagnostic value		Non-diagnostic/low diagnostic value
	Reader 1	Reader 2	Reader 1	Reader 2	Patients	Volunteers	Patients	Volunteers
non-dpTX 3.0T	1	1	2	1.5	44%	80%	56%	20%
dpTX 3.0T	2	2	2	2	98%	100%	2%	0%
1.5T	2	2	2	2	100%	100%	0%	0%

The left half of the table depicts mean values as rated by the two radiologists based on the 3-point ordinal scale in which “3” = no ghosting, “2” = ghosting not interfering with diagnostic image interpretation, “1” = severe ghosting interfering with diagnostic interpretation. The right half of the table illustrates the percentage of images deemed to have “No loss in diagnostic value” (scored as ≥ 2) vs“Non-diagnositc/Low Diagnostic Value” (scored as 1). Numbers in bold are statistically different from the other two numbers within the column.