Commitment and Contingencies (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 31, 2023	Jan. 31, 2022	Jan. 31, 2023	Jan. 31, 2022
Commitments and Contingencies [Line Items]
Royalty expense	$ 21,000	$ 87,000	$ 129,000	$ 286,000
Minimum
Commitments and Contingencies [Line Items]
Royalty fee per tumor sample			$ 0
Royalty payment, as percent of contract price			2.00%
Maximum
Commitments and Contingencies [Line Items]
Royalty fee per tumor sample			$ 30,000
Royalty payment, as percent of contract price			20.00%